Free Project Circuit Schematic

One Time Only Alarm Circuit

2011-10-07T23:16:00.000-07:00

Here’s a design circuit for sound its Siren only once. That is – when the alarm is activated – the Siren will sound for a preset length of time. Then it will switch off and remain off. The alarm will not re-activate. This is the figure of the circuit;

A range of Expansion Modules allow you to add any number of Instant Alarm Zones, Personal Attack Zones and Tamper Zones to your system. There’s also an Untimed Output Module. It will keep an internal sounder, strobe-light, lamp or whatever going after the siren has stopped. The basic circuit has a single zone with independently adjustable Exit and Entry delays. The zone will accommodate the usual types of normally-open and normally-closed input devices – such as pressure mats, magnetic-reed contacts, micro switches, foil tape and PIRs. Before you set the alarm – make sure that the building is secure – that ALL of the Green LEDs are lighting – and that the Yellow LED is off. If the Yellow LED is lighting – there’s a fault in one of the zones.

Downed Model Locator Circuit

2011-10-07T23:12:00.000-07:00

Here’s a design circuit that available for your local Radio Shack store, and modified it to decrease false triggering from low voltage spikes in the on-board power system when full sized or higher torque servos are used. This circuit is called downed model locator. Your transmitter sends a set of pulses to your receiver every 20 milliseconds, and your receiver in turn sends an individual pulse to each of your servos at the same interval. This circuit is a pulse omission detector--an alarm sounds when the pulses, originating from your transmitter, are no longer present. By plugging this circuit into an unused servo socket on your receiver, you can turn on the alarm by turning off your transmitter. This figure is show about the circuit;

The first capacitor C1 filters out DC voltage, preventing an aggressive automatic gain control of some current receivers from shutting off the alarm even when your transmitter is off. The first transistor Q1 serves to flip the pulse to negative modulation that the 555 needs. The C2 capacitor and the R4 resistor establish the time interval--if no pulse is received in the time it takes to charge the capacitor through the resistor, the alarm sounds. The interval is the resistance multiplied by the capacitance: 1uF x 47k = 0.000001F x 47000 ohms = 0.047sec = 47msec which is a little over twice the standard 20msec R/C frame rate--this device uses a little longer interval than the frame rate to prevent false triggering. The other capacitor C3 smoothes the control voltage on the 555, preventing false triggering from spikes in the supply voltage. Unless a pulse opens the Q2 transistor to drain the C2 capacitor before the capacitor is fully charged, the pin 6 threshold senses a high voltage and triggers the output pin 3 to go low, sinking current across the buzzer and making noise. With the reset pin 4 high, the discharge pin 7 drains the capacitor, and the cycle starts again.

Alarm Circuit for Refrigerator Doors

2011-10-07T23:11:00.000-07:00

The circuit in the figure will provide a beeping sound to alarm the household that the refrigerator door has been opened for more than 20 seconds. This is the figure of the circuit;

The appropriate location of the circuit should be near the lamp, if there is any, or near the opening. It should be enclosed in a small box so as not to expose the electronic components. The circuit’s operation depends on the detection of light by the phot resistor since the interior of the refrigerator will be dark once the door is closed. During this stage, a high resistance will be present at the photo resistor R2 at approximately greater than 200K Ohms. This value clamps the ripple counter and oscillator IC1 by making the Pin 12 at HIGH state.

The photo resistor will only lower its resistance at approximately less than 2K Ohms once the refrigerator bulb or lamp illuminates or when a ray of light strikes from the door opening. This will also cause Pin 12 to go LOW and will start IC1 to count. The piezo sounder or buzzer will beep for 20 seconds after a preset delay of 20 seconds by the time the fridge was left open. It will then stop after the same amount of time and will start the cycle over and over until the door is closed. The frequency of the beeping by the piezo sounder can be modified into 3 times per second by connecting the diode D2 to IC1 via Pin 6. The circuit may be powered by a 3 V battery source by connecting in series 2 1.5 V double A batteries.

Voice Changer Circuit Using RTS0072B

2011-04-28T10:44:00.000-07:00

Here’s a design circuit for very simple voice changer electronic circuit project can be designed using the RTS0072B single chip CMOS LSI designed for voice changer, which can transpose or distort one voice into another voice by encoding the input audio signals in normal speed and transmit the output audio signals with unusual speed. That is accomplished by sampling the input audio signals into digital signals and re-arranges the digital signals to generate different voice from the user normal voice. This is the figure of the circuit;

Circuit must be powered from a DC power supply circuit that will provide a fixed output voltage between 3 and 5 volts. This circuit has various voice effects like transposing voice (higher or lower),amplifying voice and robot voice. As you can see in this project is used a 9 volts DC power supply, because this circuit uses a LM386 audio amplifier IC that will amplify the output signal .

Temporary LED Lamp/Illuminator Circuit

2011-04-28T10:27:00.000-07:00

Here’s a design circuit for temporary lamp circuit is very helpful in emergency situation or in any application where we don’t have much time to turn off the lamp. Just press the push button, do a little fast task, and then leave it. This circuit hold the LED light for about 10 seconds, which should be enough for most simple tasks. This is the figure of the circuit;

This circuit works like this: when the push button S1 is pressed, the C1 will be fully charged instantly. Not only charging the capacitor, the current will supply the bias current for transistor’s base as well. This base current will activate the transistor to turn on the LED. After the push button is depressed, the capacitor C1 will keep supplying the base current for about 10 seconds, holding the LED lamp on. If you think this period is too short then you can try with different C1 values, try 47uF or 100uF and you’ll see the difference. You can use almost any type of small transistor since almost all small transistors will be capable of driving LED lamp which draw current less than 20 mA.

Car Headlights On Reminder Circuit

2011-04-28T10:26:00.000-07:00

More important than environmental issue of energy saving, avoiding car battery failure when you leave the headlamp turned on overnight in the garage is possibly more important for your concern. This is a circuit of automobile lights-on reminder if you turn off the engine but forget to turn off the main lamp, this circuit will give warning when the headlights are on. This is the figure of the circuit;

The warning can either 12V lamp or son alert (audible alert). A 2N1305 transistor is used as switch to turn on the alarm when the engine is on. This transistor receives the current from the wire that feeds the headlights. The ignition switch is used to turn on or turn off the alarm. The alarm will not active when the ignition is on which causes the transistor to bias off.

22W Amplifier for 12V Power Supply Systems Circuit

2011-04-19T06:14:00.000-07:00

Here’s a circuit for 22-W Amplifier circuit that is designed for or 12-V DC power supply Systems. There are many application for this circuit, such as in car audio application. In car electrical power supply system, the 12V power supply will be provided by the host vehicle’s battery. The capacitor C3 is used to give ripple rejection, since noisy power supply voltage is common in automotive electrical system. This is the figure of the circuit;

The power supply noise signal on car power supply is decoupled by the capacitors C2 and C1. Smaller capacitor C2 is needed to decouple the high frequency noise, since the larger cap (C1) usually has high equivalent series inductance that prevent the high frequency noise (such as glitch or spike) to be bypassed. The capacitors C5 couple the incoming audio signal to IC1 while decoupling static DC offset. For better bass response, this circuit prevent rolling off of the low audio frequencies by choosing a relatively large capacitance for small signal, 10μF capacitors. This circuit prevent power supply pop noise by muting the amplifier at the power-up. The mute input (pin 14) is fed by capacitor C6 and Resistor R1, giving delay on power-up which prevent turn-on pop. This R/C time constant gives about 1.4s delay to keep the output muted, enough to make sure the amplifier reach the stable state after powered up. About how this muting works, the amplifier will be ON if pin 14 has at least 8.5 V. The chip will remain in muted condition if the voltage at this pin is below 3.3V. This input pin need very low current consumption, only about 100 pA for standby (muted) and around 40 pA when active. The R1 values must be no larger than 100,000 Ω. The R1/C6 constant should be on the second order. If time constant is too short, the turn-on pop will still be heard, but too long time constant will give unpleasant delay.

Inductance Meter Adapter Circuit

2011-03-29T03:38:00.000-07:00

This is a design circuit for measure inductance of the inductor labeled LX which is the inductance to be measured. The o/p of the circuit is a TTL square wave whose frequency relates to the inductance being measured. The inductance meter adapter output is connected to a frequency meter and the inductance is calculated from the frequency. This is the figure of the circuit;

The center operate of the circuit is the buffer colpitts oscillator(the first stage) which resonates with the unknown inductance to give a Sine wave of a particular frequency . The frequency of the sine wave is a function of the unknown inductance and the four 1000pF capacitors. The output sine wave is amplified by the second transistor and is then rectified by the capacitor and diode combination that follows. The rectified sine wave now having only positive excursions is buffered by the third transistor and is then fed to the 74ls393. Counter IC which is configured as a divide by 256 counter. The output of the IC pin 6 and ground is connected to the frequency meter.

The parts:
The 7805 regulator powers the IC and the last 2 transistors
The circuit operates from a 9V battery which also feeds the regulator
The Ic consists of two counters in one package of 14 pins hence you need just one.
PIN 14 is VCC and PIN 7 is ground
The ic is TTl IC

LED Torch Circuit Using MAX660

2011-01-31T20:15:00.000-08:00

This is a design circuit for a simple LED torch circuit based on IC MAX660 from MAXIM semiconductors. This is the figure of the circuit;

The MAX 660 is a CMOS type monolithic type voltage converter IC. The IC can easily drive three extra bright white LEDs. The LEDs are connected in parallel to the output pin 8 of the IC. The circuit has good battery life. The switch S1 can be a push to ON switch. [Circuit diagram source: CircuitsToday.com]

How to Build a Rheostat

2011-01-31T20:13:00.000-08:00

In this figure is show about how to build the rheostat;

This is a procedure and component that is necessary to prepared.

Components
1.    The components needed for the connection are
2.    Flashlight bulb and socket [1]
3.    Dry cell lantern battery/D-cell battery [2]
4.    Wire [About 15 to 17 inches and another one 2 inches]
5.    Spring [1]
6.    Wire Clippers [A pair]
7.    A typical spring can be obtained from a widow roll up. You can even get to buy one at a cheap rate.

Procedure
·    Connect the two Dry cell lantern/D-cell batteries tail-to-tail, so that the positive polarity of one battery is connected to the negative polarity of the other.
·    Using a wire cutter, cut the wire in equal lengths. One wire should be at least 8 centimeters long.
·    Connect the wires onto the open ends of both the batteries.
·    The end of one wire must be connected to the bulb socket with the bulb in it.
·    Connect the second wire to one end of the long spring.
·    Connect the free end of one wire to one terminal of the light socket.
·    Connect the other free wire to one end of the spring.
·    Take the two inch wire and connect it to the second terminal of bulb socket.
·    Connect the other end of the two inch wire onto the other end of the spring.

How this circuit work?
As soon as the circuit is in closed loop, the bulb begins to glow. Although the glow intensity is less, when you move the wire through the spring onto the other end where the wire is connected, the bulb starts to glow more brightly. When both the wires are nearby the glow will be in its maximum. The spring is mainly made of steel wire. Steel wires are not very good conductors of electricity. Thus the resistance of the circuit also increases. If the spring length is long enough you will get to see different stages of the glow. Thus you will get to see the working of a rheostat.

Electronic Mosquito Re-peller Circuit

2011-01-31T20:09:00.000-08:00

This is a design circuit of the ultrasonic mosquito repeller. The circuit is based on the theory that insects like mosquito can be repelled by using sound frequencies in the ultrasonic (above 20KHz) range. This is the figure of the circuit;

The circuit is nothing but a PLL IC CMOS 4047 wired as an oscillator working at 22 KHz. A complementary symmetry amplifier consisting of four transistor is used to amplify the sound. The piezo buzzer converts the output of amplifier to ultrasonic sound that can be heard by the insects.

Powering LED from Single AA Cell Circuit

2011-01-29T15:36:00.000-08:00

LED has benefit that is longer lifetime than incandescent lamp, and even higher efficiency in latest LED technology. LED is also very compact, but unfortunately it needs higher voltage to operate. This is a design circuit for single cell battery (1.5v) or rechargeable cell (1.2V) cannot be used to power LED directly. Here’s the figure of the circuit;

We have to use a DC-to-DC step-up converter to enable single cell operation for LED.

Mixer or Sewing Machine Motor Speed Control Circuit

2011-01-29T15:34:00.001-08:00

This circuit will be effective to use simple half wave motor speed control with small universal ac/dc motors. Two amps RMS is the maximum current capability. The control gives excellent torque characteristics to the motor because speed dependent feedback is provided, even at low rotation speeds. Here’s the figure of the circuit;

By closing switch S1, thus bypassing the SCR, we can achieve normal operation at maximum speed. [Circuit diagram source: seekic.com]

Halogen Light Switch Circuit

2011-01-29T15:33:00.000-08:00

This is a design circuit for halogen light switch circuit works only for dc halogen lamps. Halogen lamps give a good light and have an excellent efficiency. Here’s the figure of the circuit;

This circuit is use a FET transistor because the current is dependent of the FET’s gate voltage. The maximum gate voltage is 12V, so this circuit is adequate for 12 volt lamps. R1 value is 100 kΩ for 6V and 470 kΩ for 12V. You can use BUZ10 which can outstand up to 20A or BUZ11 with maximum 30A. You do not need heat sink for this FETs because they tend to warm up to only 17 degrees Celcius.

Diode Thermometer Circuit Using 1N4148

2011-01-29T15:32:00.000-08:00

This is a design circuit of thermometer. When power transistors are used, they may tend to overheat. Likewise resistors may also overheat in the event of faults or short-circuits. The knowledge of their temperatures may be advantageous. Here’s the figure of the circuit;

Measuring the temperature of a bodies, depends upon the establishment of thermo-dynamic equilibrium between the body and the device used to sense the temperature. In practice, this condition is rarely attained since it is difficult to establish complete instantaneous equilibrium. Hence great care must be exercised in choosing a method suited to the problem so that satisfactory conditions for temperature measurements are obtained. Temperature sensors possess thermal characteristics dependent largely on their size and shape and the materials from which they are made.

Celsius Thermometer Circuit

2011-01-29T15:30:00.000-08:00

This is a design circuit of the Celsius thermometer in the diagram is based on the well-known Type LM334 from National Semiconductor. This IC is a sensor that provides a current which is directly proportional to the temperature in kelvin (K). Unfortunately, this is a quantity that is not suitable for use in most practical applications. This is the figure of the circuit;

In the circuit, therefore, the sensor is set to 1 µA K–1 with P1 and the offset of 273 K removed with P2. This renders the output voltage of the sensor directly proportional to the temperature in degrees Celsius (° C) and this makes the circuit suitable for a great many applications (since 1K=1° C). Circuit IC2 is arranged as a 2.5 V reference voltage source. The current setting of the sensor is determined by the resistance between the adjust pin and earth. If the earth is made virtual by raising the potential at the adj pin, the zero point can be shifted as desired. Calibration is best done by using a good domestic thermometer as reference. Start by short-circuiting IC2 and adjusting P1 until the reading of meter M1 shows a current value numerically equal to the ambient temperature plus 273. If, say, the room temperature is 25°C, adjust P1 until the meter reads 298 µA. Then, remove the short-circuit from IC2 and adjust P2 until the meter reads a current whose numerical value is equal to the room temperature, that is, 25 µA. The circuit draws a current not exceeding 1 mA, so using two AA size (AM3, MN1500, LR6, SP/HP7) batteries as power source will give a life of a couple of years.

Over/Under Voltage Monitor Circuit

2011-01-24T01:38:00.000-08:00

This is a design circuit for over/under voltage monitor circuit. This circuit is used to monitor Any potential from 1 to 15 V. If there is a undesirable variation was occurs, two lamps will flash. The voltage differential fro lamp turn off and turn off is about 0.2V at any setting. Low and high set points are independent of each other. The type of SCRs must be the sensitive gate type. This is the figure of the circuit;

The value of R3 depends on the type of SCR. To determine value of R3, adjust the R3 until lamp turns on when there is no signal at the SCR2 gate. The zener diode is connected in series with positive lead, so any 15-V segment can be monitored. The zener voltage plus 0.8V is the low set-point voltage. [Circuit diagram source: seekic.com]

Auto-Off Power Source

2011-01-24T01:33:00.000-08:00

This is design circuit for Auto-Off Power Source circuit. This circuit is used to turn off the power source automatically. This circuit uses the MAX931 that has key features such as high current output, an internal reference, 2.5µA supply current, and hysteresis. This circuit requires only 3.5uA quiescent current to provide voltage of Vbatt -0.12V with 10mA load. This is the figure of the circuit;

If we use the component values given, the maximum hysteresis is ±50mV which programmed by the three-resistor voltage divider and the IN-voltage is set at 100mV. So, for IN+ falling, the IN + trip threshold is approximately 50mV.

This circuit also uses RC time constant to determines the maximum power-on time of the OUT pin before power-down occur. The period is defined by following equation:
T=R x C x 4.6sec

Switching Regulator Circuit Using LM1758 A

2011-01-01T20:05:00.000-08:00

This is a circuit for a switching regulator which can easily be set up for such dc-to-dc voltage .conversion circuits as the buck, boost, and inverting configurations. This is the figure of the circuit;

The LM 1578 A features a unique comparator input stage which not only has separate pins for both the inverting and non-inverting inputs, but also provides an internal 1.0 V reference to each input, thereby simplifying circuit design and PC board layout. The output can switch up to 750 m A and has output pins for its collector and emitter to promote design flexibility. An external current limit terminal may be referenced to either the ground or the Vin terminal, depending upon the application. In addition, the LM 1578 A has an on board oscillator, which sets the switching frequency with a single external capacitor from < 1 Hz to 100 kHz (typical). It operates from supply voltages of 2 V to 40 V. It is provided with current limit and thermal shutdown. Duty cycle up to 90 %.

Water Level and TDS Sensor

2010-12-06T15:48:00.000-08:00

This is a design circuit for watel level sensor using TLC555 is a monolithic timing circuit fabricated using the Lin-CMOS* process. Due to its high impedance inputs (typically 1012 Ohms), it is capable of producing accurate time delays and oscillations while using less expensive, smaller timing capacitors then the NE555. This is the figure of the circuit;

Like the NE555, the TLC555 achieves both mono stable (using one resistor and one capacitor and astable (using two resistors and one capacitor) operation. In addition, 50% duty cycle astable operation is possible using only a single resistor and one capacitor. It operates at frequencies up to 2 Mhz and is fully compatible with CMOS, TTL, and MOS logic. It also provides very low power consumption (typically 1 mW at VDD = 5V) over a wide range of supply voltages ranging from 2 volts to 18 volts.

FSK Demodulator Circuit Using LM565

2010-12-06T15:46:00.000-08:00

This is a design circuit for the FSK demodulator, that is the electronics device that converts the FSK signal to serial digital signal. To transmit digital serial data we use FSK modulation and to get back the digital data at the receiver, we need to demodulate it. This is the figure of the circuit;

The main component of this circuit is LM565. For mark /space coding, this demodulator circuit uses 2225/2025Hz. This frequency is the answering frequency of BELL 113, 108, and 103 standards. [Circuit diagram source: National Semiconductor Application Notes]

FM Antenna Booster Circuit

2010-12-06T15:43:00.000-08:00

This is a design circuit for a low cost fm antenna booster that can be used to listen to programs from distant FM stations clearly. The antenna fm booster circuit comprises a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570 (C2570). This is the figure of the circuit;

Assemble the circuit on a good-quality PCB (preferably, glass-epoxy). Adjust input/output trimmers (VC1/VC2) for maximum gain. Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the fm antenna booster schematic.

TRIAC Basic Operation

2010-11-17T15:23:00.000-08:00

Triode for alternating current, TRIAC, is an electronic component that can control power in two direction in an AC circuit. The figure (a) shows the block construction and schematic symbol of TRIAC. The TRIAC is operated like two SCRs in parallel connection in opposite direction like shown in figure (b). This is the figure of the operation of TRIAC;

A TRIAC can be triggered by either polarity, positive and negative. It has only single gate, even though the figure (b) shows each SCR has a gate. The TRIAC operates in same direction with an SCR in forward direction because the TRIAC is operated in both directions, operating and blocking.

Digital LED Voltmeter Circuit Using ICL7107

2010-11-17T15:18:00.000-08:00

This is a design circuit for digital voltmeter with LED display. It’s ideal to use for measuring the output voltage of your DC power supply. It includes a 3.5-digit LED display with a negative voltage indicator. It measures DC voltages from 0 to 199.9V with a resolution of 0.1V. The voltmeter is based on single ICL7107 chip and may be fitted on a small 3cm x 7cm printed circuit board. The circuit should be supplied with a 5V voltage supply and consumes only around 25mA. The use of 7805 5V voltage regulator is highly recommended to prevent the damage of ICL7107, 555 ICs and to extend the operating voltages. This is the figure of the circuit;

Parts list of The Digital LED Voltmeter:
R1 = 8K2 R1 = 8K2
R2 = 47K / 470K R2 = 47k / 470K
R3 = 100K R3 = 100K
R4 = 2K R4 = 2K
R5, R6 = 47K R5, R6 = 47k
R7 = 0R / 4K7 R7 = 0R / 4K7
R8 = 560R R8 = 560R
C1,C5, C6, C8, C9 = 100n C1, C5, C6, C8, C9 = 100n
C2 = 470n / 47n C2 = 470n / 47n
C3 = 220n C3 = 220n
C4 = 100p C4 = 100p
C7 = 10-22u C7 = 10-22U
D1, D2 = 1N4148 D1, D2 = 1N4148
IC1 = ICL7107 IC1 = ICL7107
IC2 = NE555 IC2 = NE555
OPTO = CA 10 pin FTA = CA 10 pin

Differential Analog Switch Circuit

2010-11-17T15:15:00.000-08:00

This circuit is design circuit for a differential analog circuit switches. The FM1208 monolithic dual differential multiplexer used in applications where the RDS (ON) must be the same match. Since RDS (ON) for monolithic dual tracks at better than 1% of the broad temperature range (-25 to 125 C) is making an unusual choice, but ideal for a multiplexer accurate. This greatly reduces the close tracking errors due to common mode signals. OP-Amp is used LM107. This is the figure of the circuit;

Circuit source: National semiconductor Application

Complementary Pair Vertical Deflection Pre-Amp Circuit

2010-11-17T15:14:00.000-08:00

This is a design circuit for Complementary Pair Vertical Deflection Pre-Amplifier circuit. This circuit is modification circuit of Vertical Deflection Pre-Amplifier for 100MHz scope. This circuit remove few resistor-capacitor combination from the original circuit. That components can be removed because they tweaked the response of the amplifier at high frequencies, so no problem. The second two transistors receive +2V from the two 1N4733 5.1V zener diodes. But the two 1N4733 5.1V zener diodes can be replaced with 10V zener. This is the figure of the circuit;

This circuit use a complementary pair of an npn and a pnp transistor. In other words coupling capacitors are not needed. This circuit has low output impedance about 2.6R. This circuit has small AC agin of 2.0, because of strong series-shunt feedback between the two transistors. The most of the bias current of the npn transistor, flows not through the emitter capacitor but through the feedback to ground. The basic amplifier is loaded by the feedback network.

10.7-MHz IF Amplifier Circuit

2010-11-17T15:12:00.000-08:00

This is a design circuit for 10.7-MHz IF amplifier circuit. This circuit is used in many application such as cell phone base station receivers (final IF) and FM broadcast receivers. The ceramic filter that is used in this circuit is cheap and available in a variety of insertion losses and bandwidths. This circuit uses a 230-kHz bandwidth filter SFELA10M7GA00-B0 and the gain stage. This is the figure of the circuit;

The second figure shows the circuit response. The insertion loss of this circuit is 4 dB. However, actually the insertion loss is slightly more than 4dB. In the pass band, the slight nonlinearity has more to do with the ceramic filter’s characteristics than with the op amp. The circuit’s impedances are different from a nominal load of 50 Ohm, so the response should be corrected. Actually, a 280-Ohm resistor and the 50-Ohm instrument as the load that is configured in series connection measures the response. The voltage divider in this circuit is used to compensate that effect.

Motion (Motor) Control Servo System Block Diagram

2010-10-16T03:52:00.000-07:00

This is a figure for a block diagram of a modern automated systems incorporate closed-loop feedback for motion control. They typically include a servo system that consist of feedback elements and motor driver combined in a manner. This will give accurate and stable control over speed and position. Below is the illustration of the various system-level components of a typical servo system. This is the figure of the diagram;

For processing the high-speed encoder signals, typical motion-controller cards and modules include a motion-control IC, a microprocessor, and a DSP or custom ASIC. Velocity and direction of rotation signals to the driver or amplifier is provided by the controller which in turn provides the proper levels of voltage and current (power) to operate the motor. We must have address the following items at the system level to design robust and fault-tolerant motion-control system with feedback during design: Controller-encoder input circuits (receiver circuits), Receiver circuit PC-board layout and Encoder-signal cabling system. Motion-controller inputs, such as hard-wired emergency stop and limit inputs, should also be considered when designing a fault-tolerant feedback system though not addressed in this article.

Low Drop Out (LDO) Voltage Regulator Circuit Using Discrete Semiconductor

2010-10-16T03:47:00.000-07:00

There are several integrated circuit chips designed specially for LDO (low drop out) voltage regulator. Building LDO using standard op-amp and discrete components can be an alternative. This is the figure of the circuit;

To design the circuit, this is the guideline to change the value of components;
·    D1 is chosen for the best performance, the sharper the on-off transition curve the better. Some people say that 5,6V Zener diode has better voltage regulation than other voltage. But you can actually use any voltage below the expected minimum output voltage. The output voltage will be Vd(R4+R3)/R3, with Vd is the voltage of the Zener diode D1.
·    R1 is selected so the exact voltage of D1 will have minimum drift over the input supply range variation. Look at the D1 datasheet. R1 is usually not critical, and you can use larger value to save the current loss.
·    R3 and R4 uses to set the expected output voltage, and are chosen as large as possible to conserve the current loss, but should be much smaller than the op-amp’s input impedance.
·    Q1 is chosen for the lowest Vce drops for the best performance, the higher gain (hFe), and the collector current must be capable to handle the expected maximum load current.
·    Q2 must have low drop Vce if the regulator is expected to regulate low voltage source, but not so critical if the input supply voltage is high.
·    R2 can be selected to make sure that Q2 is always “on” even when the regulator is unloaded. Just remember that the voltage across R2 is same with Vbe of Q1, you can set the value of R2 to set the current Ice of Q2 at the best of Q2′s Ibe/Ice curve.
·    Select The op-amp A1 for the best high gain, highest input impedance. The most important character for A1 is that the output swing should be capable to go down below Q2 Vbe turn-on point.

LM1893 Power Line Modem Circuit

2010-10-16T03:44:00.001-07:00

This is a circuit for an LM1893 power line modem circuit. This circuit is used to transfer information between remote location by using the power mains. This circuit uses LM1893 that is used as a power line interface for half-duplex (bi-directional) communication of serial bit stream of virtually any coding. This is the figure of the circuit;

To give maximum range, impulse noise filter and a PLL-based demodulator are combined in reception. In transmission, a sinusoidal carrier is impressed and FSK modulated on most any power line via rugged on-chip driver. Besides LM1893, this circuit also uses a COPS controller and discrete components. [Circuit schematic source: National Semiconductor Notes]

Discrete Active Virtual Ground Circuit

2010-10-16T03:35:00.000-07:00

This is a circuit for a schematic diagram shows that you can build such circuit using discrete components. This circuit uses most any complementary pair of small-signal transistors such as PN2222A and PN2907A. The diode that is used in this circuit is generic small-signal types like 1N914. This is the figure of the circuit;

You can also use other transistor type as long as you choose from high gain one (al least hfe=100), almost any silicon type will work. Choose one that the current handling capability suits your need. The advantages of this circuit are the parts cost is lower than for any other circuit and has better performance than a simple resistive divider virtual ground. It is, however, the least accurate of the buffered virtual ground circuits.

Digitally Controlled Phase Shifter Circuit

2010-10-16T03:23:00.000-07:00

This is a circuit for the circuit implementation of phase shifter circuit is well suited to using digital potentiometer to control the resistive control element of the phase shifter. This is the figure of the circuit;

The phase at a given frequency is now under control of a digital signal using this circuit which is optimized for phase-shifting over the audio range. By using a single digital control line, the DS1669 used here can have its wiper position set to cause the wiper position increment upon each low-going pulse, until it reaches the upper end of the pot, when it will reverse direction and decrement.To cause the phase constantly sweep (an effect commonly used in popular recordings today), we can supply a clock to this digital control input. The digital potentiometer is biased at 1/2 VCC since this is a single supply circuit. [Circuit schematic source: maxim-ic application notes].

3 Phase AC Motor Speed Control Circuit

2010-10-16T03:17:00.000-07:00

Controlling the speed of three phase ac motor is done by controlling the frequency of the power line supply, since the motor is synchronized with the line frequency. Three phase ac motor speed controller is actually nothing more than three phase sine wave power inverter with variable frequency. The three phase power inverter is a complex circuit, but fortunately there is an integrated circuit chip for this purpose. This is the figure of the circuit;

For the final motor driver circuit, you can see the component values are shown only for OB2 channel, but the others are similar. This 3 phase ac motor controller use optical isolation, so you must be careful in designing the layout, to make a clear separation between low and high voltage network. This separation is useful for minimizing the risk of hazardouz electrical shock.

Tone/Frequency Detector Circuit

2010-09-26T09:02:00.000-07:00

This is a design circuit for tone/frequency detector (decoder) circuit that can be used to detect the presence of a signal with a certain tone. The output of the circuit will be active if the signal is the same tone with the tone of a series of internal oscillator. LM567 is one of decoder that we can use. This is the figure of the circuit;

The LM567 and LM567C are general purpose tone decoders. Both are designed to provide a saturated transistor switch to ground when an input signal is present within the pass band. The circuit consists of an I and Q detector. Both, I and Q detector are driven by a voltage controlled oscillator which determines the center frequency of the decoder. To independently set center frequency, bandwidth and output delay, external components are used.

Oscillator internal frequency of the circuit is:
f = 1/(1.1xR1xC1)
The output will be low level logic if the input signal has a minimum voltage of about 25 mV and the frequency around the frequency of internal oscillator.

Temperature Sensor Circuit Using LM335

2010-09-26T09:01:00.000-07:00

This is a design circuit for a temperature sensor circuit that uses an LM335, an IC that converts the ambient temperature into an equivalent output voltage. The voltage output of an LM335 increases by approximately 10 mV for every 1 degree Kelvin of rise in temperature. Note that 1 degree Kelvin is equal to 1 degree Celsius. This is the figure of the circuit;

In this circuit, the output of the LM335 is fed into a 741 op-amp (any standard op-amp may be used) which is configured as a voltage follower. As such, the output of the 741 is the same as the voltage output of the LM335. The main function of the op-amp, therefore, is just to buffer the LM335 output so that it is not affected by whatever load is connected to this temperature sensor circuit. This circuit can be used for measurement purpose.

Op Amp Based Sound Detector Circuit

2010-09-26T08:21:00.000-07:00

This is a circuit that can be used for detecting sounds and providing an output signal when a sound is detected. This output signal may be fed to another circuit that sets off an alarm when the signal is received. This circuit is therefore useful in security applications. This is the figure of the circuit;

The circuit uses a condenser microphone to pick up sounds from the environment. This is a powered microphone, which makes it more sensitive than ordinary microphones. The microphone transforms the sound waves into an electronic signal that is fed to the 741 op amp.

The 741 op amp in this circuit is configured as a single-supply inverting amplifier. Adjust R1 to maximize the sensitivity of your circuit. C1 and C2 are used to block the DC component of the signals, so that only the AC component carrying the sound information reaches the output transistor Q1. Note that the output, which is taken from the collector of Q1, is inverted with respect to the output of the 741 amplifier.

Light Controlled Oscillator Circuit

2010-09-26T08:16:00.000-07:00

This is a circuit for a light-controlled oscillator, i.e., an oscillator whose output frequency increases with the amount of light shining on it. The main components of this circuit are the 741, a general purpose operational amplifier IC, and the light-dependent resistor or photocell, which serves as the circuit's light collector. This is the figure of the circuit;

The 741 in this circuit is configured as an oscillator driving a piezoelectric buzzer. The output voltage of the 741 is used as input voltage to the inverting input, which forces the output of the 741 to go back to the opposite level every time it changes state, causing it to toggle between 'low' and 'high' continuously. When the output of the 741 becomes low, this is fed back to the inverting input, causing the 'high' voltage at the non-inverting input to 'dominate' and force the 741 output to go back to 'high'. When the output of the 741 goes 'high', this is again fed back to the non-inverting input, which drives the output to go low, and the cycle starts over again.

The rate at which the output oscillates depends on how fast capacitor C1 charges and discharges, which in turn depends on the resistance across the light-dependent resistor or photocell. The more light shining on the photocell, the lower is its resistance. The lower the resistance, the faster capacitor C1 charges or discharges, and the higher is the frequency at which the 741's output oscillates. This is why this circuit is a light-controlled oscillator - its frequency of oscillation increases as the light shining on it increases.

DC Voltage Polarity Inverter Circuit

2010-09-26T08:13:00.000-07:00

This is a design circuit for a circuit that outputs a -Vcc voltage, i.e., an output voltage Vout that is almost the same level as Vcc but opposite in polarity. Note that this circuit can only provide a limited amount of negative current at Vout, i.e., just enough to power small dual-supply IC's. This is the figure of the circuit;

The circuit uses a 555 timer IC configured as ana astable multi vibrator, i.e., it generates a continuous square wave signal of a set frequency as long as its reset pin (pin 4) is held high. This means that the 555 output toggles between '1' and '0' continuously at the set frequency. When the 555 output (pin 3) is at logic '1', its voltage level is very close to the Vcc level, causing C2 to charge to this level through D1 while D2 isolates C3 from the 555 output. When the output is at logic '0', C2 can not discharge to pin 3 through D1 because D1 is not conducting. C2, however, can discharge its near-Vcc voltage to pin 3 through D2. This, in effect, puts the anode voltage of D2 (Vout) at close to negative Vcc. C3 stabilizes this -Vcc voltage with respect to GND.

Multiple Voltage (+/-12V and +/-5V) Power Supply Circuit

2010-09-22T23:26:00.000-07:00

This is a design circuit for a power supply circuit that provides +12V, -12V, +5V, and -5V regulated outputs. This is just a more complex derivative of a basic negative/positive voltage supply. This is the figure of the circuit;

Two separate sets of transformer and diode bridge are used to generate the +/-12V and the +/-5V, but the rectification circuits are almost identical. The only difference is the voltage regulator IC's used. The 7812 and 7912 are used to regulate the +12V and -12V outputs, respectively. The 7805 and 7905, on the other hand, are used to regulate the +5V and -5V outputs, respectively. Note that these voltage regulator IC's need to be attached to adequate heat sinks if used in applications that require high power.

Low Voltage AC Voltmeter Circuit

2010-09-22T23:23:00.001-07:00

This is a design circuit for AC voltmeter for measuring low AC voltages. The main component of this circuit is an operational amplifier (such as the 741 or 351), configured as an amplifier whose feedback circuit is a diode bridge full-wave rectifier. This is the figure of the circuit;

The op amp's output current in both the positive and negative cycles flows through it in only one direction. In effect, the average of the op amp's output ac current io, which passes through the ammeter as a dc current, is measured by the ammeter. With full wave rectification, the meter current is given by: io = 0.9 Vin/R, or Vin = 1.1 ioR. Note that this project requires calibration so that the meter will register the rms value of the input voltage Vin.

Low Cost Buffered Voltage Reference Circuit

2010-09-22T23:22:00.000-07:00

This is design circuit for a low-cost voltage reference circuit. Its main component is a general-purpose operational amplifier, the 741, configured to output a buffered fixed reference voltage for use by other IC's or circuits, such as an Analog-to-Digital Converter (ADC). This is the figure of the circuit;

The reference circuit above is designed to output 5 volts, and employs an AD589 as the 741's own reference. The AD589 is a low-cost, temperature-compensated bandgap voltage reference that provides a constant output of 1.23 V. Thus, the voltage at both inputs of the 741 is 1.23 V, which is also the voltage at the junction of the 1K and 3K resistors connected to the inverting input. This forces the 741 to output a steady voltage of approximately 5V (1.23V x 4K/1K = 4.92V).

Flame Detector Circuit

2010-09-22T23:16:00.000-07:00

This is a design circuit for a detecting the presence of fire. This simple project is often incorporated in small roving robots - the ones that robotics hobbyists love to build. This is the figure of the circuit;

A flame, even one that is barely visible, emits significant infrared content. Thus, the sensor of this circuit is an infrared-sensitive phototransistor Q1, which is basically a transistor whose base is excited by infrared rays instead of input current. As more infrared rays shine on Q1, the more conductive it becomes. When there is a flame or fire nearby, Q1 will conduct, feeding current to the base of Q2. At a certain threshold, this current will be large enough to turn on Q2, which will pull down the base of Q3. This will turn off Q3, causing Vout to be pulled high. Vout may be used to excite a light-emitting diode or an alarm circuit.

In the absence of a nearby source of IR rays, Q1 will be 'off', and so will Q2. This will allow the base of Q3 to remain 'high', causing Q3 to remain 'on' to pull Vout to 'low'. This circuit will require optimization of the sensor position and experimentations with the R1 and R3 values to achieve the proper sensitivity. An infrared filter might also be required by the phototransistor if it is being affected by too much ambient light.

Event Interruption Alarm Circuit

2010-09-17T08:52:00.000-07:00

This is a design circuit for an event interruption alarm circuit, or a circuit used for sounding off an alarm if an expected event does not happen. The occurrence of the event is represented in the circuit above by switch S1, i.e., the switch S1 is momentarily closed every time the expected event occurs. This is the figure of this circuit;

The main component of this circuit is the 555, a versatile timer IC. It is configured as a mono stable multi vibrator, i.e., a circuit which will output a single pulse at pin 3 every time pin 2 is pulled 'low'. Each time the event occurs, switch S1 closes, discharging C1 to ground through Q1 and triggering pin 2 to force an internal flip-flop to set pin 3 to a 'high' level. At this stage, the buzzer is silent since both of its terminals are 'high'. Meanwhile, capacitor C1 charges up again through R2 as soon as S1 is opened. The voltage across C1 will continue to rise unless S1 is momentarily closed again to discharge it through Q1. Momentarily closing S1 regularly before the time limit is up will prevent C1 from charging up to the critical voltage level, thereby keeping the buzzer silent.

If, however, S1 is not closed within the set time limit, the voltage across C1 will become high enough to trigger the internal flip-flop to set pin 3 to a 'low' level. At that point, the self-oscillating buzzer will alarm because pin 3 is now pulling one of its terminals to 'low' while the other terminal is at Vcc.

Dynamic Compressor, Self Powered Circuit

2010-09-17T08:45:00.000-07:00

This is a circuit for dynamic compressor will give about 20dB compression, at very wide input signal range 100 mV to 10 V. Another advantage of this circuit is that this circuit doesn’t need any power supply, we call it self powered, or more accurately, signal-powered compressor. This is the figure of the circuit;

A part of the signal is rectified by D1 and D2 and is used to charge C1 and C2 Capacitors. This current control the attenuator diodes D3 and D4, together with R3, R5, and R6. The attenuator diodes work at the nonlinear region of the forward current curve. At low level, the input signal is not attenuated since the rectified voltage is under voltage bias of D3 and D4, since that D3 and D4 become non-conductive. If the level of input signal increase, at some point, the D3 and D4 begin to conduct and attenuate the signal.

The attack time of this compressor circuit is fixed and is determined by time constant of C1, C2, R2, and the output impedance of the input source that feed this compressor input. The decay time can be slightly adjusted by R7 variable resistor. You can see that the signal path of this compressor circuit use a 470k resistor as the attenuator, means that you should only connect the output of this circuit to a high impedance stage. This circuit works best with germanium diodes, since it has lower forward bias voltage and also smoother curve than silicon diodes. Using silicon diodes will works but the performance would be degraded.

Digital Voltmeter Circuit

2010-09-17T08:41:00.000-07:00

This is a design circuit for digital voltmeter circuit. The integrated circuit ICL7107 is a 3-1/2 digit LED A/D convertor. It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers. The auto-zero adjustment mechanism ensures zero reading for 0 volts input. The circuit is classic design and you can be sure that it will work fine. However, for better result, it is recommended to design a proper PCB for minimum voltage drift and noise. This is the figure of the circuit;

Connect the positive and negative probes PLG1 and PLG2 to two points of the electric circuit you would like to know their electric potential difference or simply voltage. You have to set the selector switch S2 to proper voltage range you expect those two points would have. To calibrate the volt-meter, use the potentiometer P1. Adjust it to read correct voltage on the display by connecting probes to a known voltage source. You may need to use another calibrated volt-meter in this case.

Carlin Fuzz Compressor: Two Guitar Effects in One Box

2010-09-17T08:39:00.000-07:00

This is an easier to manage if we put the distortion and the compressor effect in one box. This Carlin fuzz compressor use unique method to give sustain and distortion effect in mixed circuit. Seem that the circuit do the dynamic compression and distortion in a single negative feedback loop. This is the figure of the circuit;

The dynamic compression is done by the FET (field effect transistor) 2N5457. If the output amplitude is high, the FET will conduct more current and short the signal to ground, and vice versa. This negative feedback loop will stabilize the amplitude, giving more gain with low level input, and less gain with high level input. The result, the output will be almost at a constant level. The note will last longer as the gain increase as the signal input fade out.

A Twin T Passive Notch Filter

2010-09-17T08:37:00.001-07:00

This is a circuit for notch filter is a circuit that rejects a very narrow band of frequency. This is a passive filter. This is the figure of the circuit;

A common application of a notch filter is the removal of the 60-Hz hum from an AC line. The twin-T filter, one of the most commonly used notch filters, is a passive filter composed of two T-networks. One of these T networks has one resistor and two capacitors, while the other has two resistors and one capacitor.

555 IC PWM Controller: Grounded and Ungrounded Load

2010-09-17T08:36:00.000-07:00

This is a circuit for PWM controller circuit. While keeping the oscillator frequency relatively stable, this 555 based PWM controller features almost 0% to 100% pulse width regulation using the 100k variable resistor. To give a frequency range from about 170Hz to 200Hz , the frequency is dependent on the 100k pot and 100n. This is the figure of the circuit;

You can see the charging and discharging of the 100n cap is done through output pin 3, and this provide a push-pull symmetric drive for easy pulse-width setting. You can see two versions, the left side for grounded load, and the right side for ungrounded load. The grounded one use pin 7 to drive the transistor, while the ungrounded one use the same push-pull output pin3, this difference is needed because wen need an inverted phase to provide consistent potentiometer scale on both version.

Low Voltage AC Voltmeter Circuit

2010-09-14T08:38:00.001-07:00

Passive Baxandall Tone Control Circuit

2010-09-05T08:16:00.000-07:00

This is a design circuit for tone control circuit using variant Baxandall. Variation of the famous Baxandall circuit is shown in the passive circuit in figure 1. Smoothly increasing +- 6 dB/octave slope of boost or cut is the feature of this circuit. Although the “shelves” are outside the audible range with these component values, the bass and treble filters have a shelving response. This is the figure of the circuit;

The threshold and shelving frequencies is predicted by the filter equations in figure 1a.The wiper shorts out the .033uf capacitor, when the bass control is rotated for maximum boost. A frequency dependent voltage divider that determines the shelf frequency of the boost are formed by R3 and C4. The wiper bypasses the 10K resistor. C1 and R2 form a high pass filter, when the treble control is set for maximum boost. The circuit uses commonly available parts to simplicity. Radio Shack sold even the 100k log taper pots, which are usually hard to find, as part number 271-1732 (in a stacked configuration for stereo). The pot will have about 10K on one side and 90K on the other at the midway point. The side with 10K parallels R2 for the treble control. The side with 10K parallels C4 for the bass control. Note that this circuit could be divided for an individual bass or treble control (R5 may then be omitted – it helps isolate the bass from the treble circuit when the two are put together). To avoid loading the network and affecting the response curves, the passive Baxandall must see a low impedance source and drive a high impedance load.

Barometer Signal Conditioner Circuit

2010-09-05T08:14:00.000-07:00

This is a circuit for a complete barometric pressure signal conditioner that operates from a single 1.5V battery. We can get the best accuracy and stability if we use bonded strain gauge and capacitive-based transducer, but they are expensive. This design introduce a new type of semiconductor transducer that achieves 0.01″ Hg (inches of mercury) uncertainty over time and temperature. This would be suitable for portable application since it uses only a single cell battery. This is the figure of the circuit;

The 6 k Ohm transducer T1 need exactly 1.5mA excitation current, so it needs a relatively high voltage source. Non-inverting input of A1 senses T1’s current by monitoring the voltage drop across the resistor string in T1’s return path. The inverting input of A1 is fixed by the 1.2V LT1004 reference. The output of A1 biases the 1.5V powered LT1110 switcher. This switcher produces two outputs from L1. The rectified and filtered voltage from pin 4 is used to supply the power for A1 and T1. A1’s output, in turn, closes a feedback loop at the regulator. This loop control the step-upped voltage to give a constant current of 1.5mA through T1. This circuit design produce the required high excitation voltage while minimizing power consumption. This is done by making the switching regulator produces only enough voltage to satisfy T1’s current requirements. Pin 1 and 2 of Li produce a fully floating, boosted voltage, which is rectified and filtered to power A2. Since A2 floats with respect to T1, it can look differentially across T1 outputs (pin 10 and 4). Practically, pin 10 acts as ground and pin 4′s output is measured by A2 using this reference point.

The gain of A2 is set to provide a convenient scale of 3.000 V = 30.00″ Hg. Calibrating this circuit is easy, just adjust R1 for 150mV across the 100 Ohm resistor in T1′s return path. This step set the T1 current to the calibration point as specified by the manufacturer. Next, adjust the scale to match the factor of 3.000V=30.00″Hg by adjusting R2. Even if the pressure standard is not available, we can calibrate the circuit using individual calibration data provided by the manufacturer. This circuit maintain 0.01″Hg accuracy over months over a wide range ambient pressure shift. This portable device is also give interesting altitude indication if we take it when driving over hills and freeway overpasses, since 0.01″Hg corresponds to about 10 feet increase from sea level. This circuit draws 14mA from the battery, permitting the circuit to operate for 250 hours if we use a single D cell battery.

Pulse Generator And Signal Tracer Circuit

2010-08-31T08:32:00.000-07:00

This is a simple circuit that is can generates narrow pulses at about 700-800Hz frequency. The pulses, containing harmonics up to the MHz region, can be injected into audio or radio-frequency stages of amplifiers, receivers and the like for testing purposes. This is the figure of the circuit;

This circuit is work if Q1 & Q2 form a complementary astable multivibrator, whose operating frequency is set mainly by R3, C2 & C3 values. Output pulses are taken at Q2 Collector and applied to the probe by means of decoupling capacitor C1. D1 provides a symmetrical shape for the output waveform. If an earclip or headphone jack is plugged into J1, the connection from Q2 Collector and C1-C2 is broken by the switch incorporated into J1: in this case the circuit becomes a two-stage amplifier.

2010-08-17T06:32:00.000-07:00

60W Guitar Amplifier Circuit
This is a circuit for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker. This is the figure of the circuit;

The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure. The preamp is powered by the same 60V rails as the power amplifier, allowing to implements a two-transistor gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability. The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice. T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected. D1 and D2 can be any Schottky barrier diode types. With these devices, the harmonic modifier operation will be hard. Using for D1 and D2 two common 1N4148 silicon diodes, the harmonic modifier operation will be softer.

Part Amplifier:
R1__________________6K8    1W Resistor
R2,R4_____________470R   1/4W Resistors
R3__________________2K   1/2W Trimmer Cermet
R5,R6_______________4K7 1/2W Resistors
R7________________220R   1/2W Resistor
R8__________________2K2 1/2W Resistor
R9_________________50K   1/2W Trimmer Cermet
R10________________68K   1/4W Resistor
R11,R12______________R47   4W Wirewound Resistors
C1,C2,C4,C5________47µF   63V Electrolytic Capacitors
C3________________100µF   25V Electrolytic Capacitor
C6_________________33pF   63V Ceramic Capacitor
C7_______________1000µF   50V Electrolytic Capacitor
C8_______________2200µF   63V Electrolytic Capacitor (See Notes)
D1_________________LED    Any type and color
D2________Diode bridge   200V 6A
Q1,Q2____________BD139    80V 1.5A NPN Transistors
Q3_____________MJ11016   120V 30A NPN Darlington Transistor (See Notes)
Q4_____________MJ11015   120V 30A PNP Darlington Transistor (See Notes)
SW1_______________SPST Mains switch
F1__________________4A Fuse with socket
T1________________220V Primary, 48-50V Secondary 75 to 150VA
                  Mains transformer (See Notes)
PL1_______________Male Mains plug
SPKR______________One or more speakers wired in series or in parallel
                  Total resulting impedance: 8 or 4 Ohm
                  Minimum power handling: 75W

Part Pre Amp:
1,P2______________10K   Linear Potentiometers
P3_________________10K   Log. Potentiometer
R1,R2______________68K   1/4W Resistors
R3________________680K   1/4W Resistor
R4________________220K   1/4W Resistor
R5_________________33K   1/4W Resistor
R6,R16______________2K2 1/4W Resistors
R7__________________5K6 1/4W Resistor
R8,R21____________330R   1/4W Resistors
R9_________________47K   1/4W Resistor
R10_______________470R   1/4W Resistor
R11_________________4K7 1/4W Resistor
R12,R20____________10K   1/4W Resistors
R13_______________100R   1/4W Resistor
R14,R15____________47R   1/4W Resistors
R17,R18,R19_______100K   1/4W Resistors
C1,C4,C5,C6________10µF   63V Electrolytic Capacitors
C2_________________47µF   63V Electrolytic Capacitor
C3_________________47pF   63V Ceramic Capacitor
C7_________________15nF   63V Polyester Capacitor
C8_________________22nF   63V Polyester Capacitor
C9________________470nF   63V Polyester Capacitor
C10,C11,C12________10µF   63V Electrolytic Capacitors
C13_______________220µF   63V Electrolytic Capacitor
D1,D2____________BAT46   100V 150mA Schottky-barrier Diodes (see Notes)
Q1,Q3____________BC546    65V 100mA NPN Transistors
Q2_______________BC556    65V 100mA PNP Transistor
J1,J2___________6.3mm. Mono Jack sockets
SW1,SW2___________SPST Switches

Fan Control Circuit Using NTC and TL082

2010-08-17T06:25:00.000-07:00

This is a circuit for fan control that is a simple circuit. This is the figure of the circuit;

R1 15k ohm resistor. NTC Thermistor- 10k ohm, sold at Radio Shack in the states. P1 10k ohm potentiometer - sets the low speed(voltage) of the fans at the cool temperature. P2 50K ohm potentiometer - sets the gain of the circuit - how fast the voltage will rise to full output when the temp is higher. TL082 a op-amp that I had handy, most any single voltage op-amp should work. The TL082 is a dual op-amp if you want more then one controller on a board. note that the power and ground connections for the op-amp are not shown on the schematic. R2 - The TL082 is a fast op-amp, needed R2 to reduce oscillation. IRF-510 A 4 amp mos-fet in a TO-220 case. Bascially as the voltage on the gate rises the mos-fet will conduct more current. note 1 there are also IRF-520 and 530 versions that will handle more current. note 2 Even at 5 watts the mos-fet will disapate some heat and will need to be heat-sinked or at least in the air flow path. the large metal part of the fet will be at drain(D) voltage level. Do not attach to case.

D1, almost any diode, 1N4001 should work,it conducts back around the fan when the mosfet turns off. As the fan continues spinning it will produce a voltage on the drain lead of the fet. D1 will limit that voltage. Adjustment, easiest if you have a voltmeter but can be done without. Get the thermistor at room temp. Adjust P1 for the low speed that you want your fans to run at. Heat the thermistor to the high temp you want the fans at full speed. ( I stuck it under my tongue) Adjust P2 until the fans are at full speed( with voltmeter the highest voltage you can get) then adjust P2 until the speed/voltage just begins to drop off. Most fan specs that I have seen show a low voltage limit of around 7 volts. Some of the smaller 80mm fans have a lower limit of 8 volts. If you set the low voltage to low the fans may stall until the thermistor heats up enough. Let me know if you build this circuit and how it works for you. corrected, single voltage op-amps should be used, OP-07 is a dual voltage.

2 Transistor FM Voice Transmitter Circuit

2010-08-17T06:23:00.000-07:00

This is a circuit for voice transmitter using a pair of BC548 transistors in this circuit. Although not strictly RF transistors, they still give good results. I have used an ECM Mic insert from Maplin Electronics, order code FS43W. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. This is the figure of the circuit;

The coil L1 was again from Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on my prototype tuned from 70MHz to around 120MHz. The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points. One final point, don't hold the circuit in your hand and try to speak. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations.

Traffic Light Circuit

2010-08-14T16:43:00.000-07:00

This is a circuit for design traffic light. This activity operates red, amber and blooming LEDs in the actual arrangement for a distinct UK cartage light. The time taken for the complete red – red & amber – blooming – amber arrangement can be assorted from about 7s to about 2½ account by adjusting the 1M preset. Some amber LEDs afford ablaze that is about red so you may adopt to use a chicken LED. This is the figure of the circuit;

The 555 astable ambit provides alarm pulses for the 4017 adverse which has ten outputs (Q0 to Q9). Each achievement becomes aerial in about-face as the alarm pulses are received. Appropriate outputs are accumulated with diodes to accumulation the amber and blooming LEDs. The red LED is affiliated to the ÷10 achievement which is aerial for the aboriginal 5 counts (Q0-Q4 high), this saves application 5 diodes for red and simplifies the circuit.

Lab Power Supply Circuit

2010-08-14T16:40:00.000-07:00

This is a design circuit for power supply. This circuit can be built no on a piece of copper-laminate. The Bench Power Supply was designed to use old lantern batteries, “D”, and “C”. This circuit can produce at least 12v -14v from old batteries and cells. As a heat-sink, this circuit uses a board. To connect the components, enamelled wire is used. To keep the transistor cool, it can be bolted. This is the figure of the circuit;

The zener is used to regulate The output of this power supply. So, there is voltage approx 1.7v across a red LED and 8.2v between the base-emitter leads of a BC547 transistor (in reverse bias). This circuit can give 0v – 9v at 500mA depending on the life left in the cells used. To indicate the circuit is ON, LED is used. The 10k pot is used to adjust the output voltage.

Guitar Pre Amp Circuit

2010-08-14T16:38:00.000-07:00

This is a circuit for guitar pre amp that has a few interesting characteristics that separate it from the “normal” – assuming that there is such a thing. This is simple but elegant design, that provides excellent tonal range. The gain structure is designed to provide a huge amount of gain, which is ideal for those guitarists who like to get that fully distorted “fat” sound. This is the figure of the circuit;

However, with a couple of simple changes, the preamp can be tamed to suit just about any style of playing. Likewise, the tone controls as shown have sufficient range to cover almost anything from an electrified violin to a bass guitar – The response can be limited if you wish (by experimenting with the tone control capacitor values), but I suggest that you try it “as is” before making any changes.

Positive Voltage Doubling Circuit using ICL7660 Voltage Doubler

2010-08-09T17:24:00.001-07:00

This is a circuit for voltage doubler that can be connected to function as voltage doublers in order to generate output voltage. The schematic herein appears positive voltage doubling circuit using the ICL7660. This is the figure of the circuit;

In this circuit, the pump inverter switches of the ICL7660 is used to charge C1 to a voltage level of the supply voltage (V+) and the forward voltage drop (Vf) of diode D1. Voltage on C1 plus the supply voltage is applied through diode D2 to capacitor C2. And the source resistance of the output will depend on the output current.

Multi Channel Link Transmitter Circuit

2010-08-02T01:50:00.000-07:00

This circuit is a multi-channel link is considerably more complex than a single channel design but it offers the possibility of designing a project that has more features. The multi-channel transmitter shown in the figure has forward, stop, reverse as well as left, centre, right steering. This is the figure of the circuit;

When the transmitter is not operating, the receiver picks up hash (background noise) and no outputs are activated. This represents the STOP function. When the forward function is selected on the transmitter, the square-wave oscillator operates at its high frequency setting, with an equal mark-space ratio. If left-turn is selected at the same time, the mark-space ratio is altered to 1:3 while the frequency remains the same. If right-turn is selected, the mark-space ratio is 3:1, with the same frequency. If the reverse function is selected, the frequency of the oscillator is reduced to half and if the centre steering is selected, the mark space ratio is 1:1. If the left steering is selected, the mark-space ratio is 1:3 and if right steering is selected, the mark-space ratio is 3:1. To understand how the channels are produced, you need to know how a multi vibrator works.

Multi Channel Receiver Circuit

2010-08-02T01:49:00.000-07:00

This is a circuit for receiver circuit. The receiver is required to pick out the signal from the noise and it does this by a process called integration and differentiation where the signal is detected due to its regular nature and this is used to charge a capacitor. This is the figure of the circuit;

Two outputs drive the motor in the forward/reverse direction and 4 outputs drive the transistors for the steering motor. The steering motor is simply a rotary actuator. This is similar to the armature of a motor, positioned inside a circular magnet. The armature does not need brushes as it will only turn about 45° in one direction and 45° in the opposite direction, depending on the direction of the current. The output of the shaft will be connected to a lever to steer the front wheels. The chip controls the two diagonally opposite transistors for the clockwise and anticlockwise rotation to get left and right steering. All the rest of the circuit has been previously discussed and the only new feature is the tapping at 4.5v for the motor. A diode on the 4.5v rail drops the voltage to 3.8v and the two output transistors drop a further 1v, so that motor receives about 2.8 to 3v.

A Split Supply Receiver Circuit

2010-08-02T01:48:00.000-07:00

This is a design circuit for receiver circuit that have better sensitivity due to the inclusion of one extra stage of amplification and the use of a higher rail voltage. This is the figure of the circuit;

The higher rail voltage gives some stages a higher gain due to the higher amplitude of the signal. But some of the gain has been lost in the diode pump as this type of pump requires more energy to charge the 10u than a 0.47u. The use of a center-tapped voltage source saves two transistors in the bridge network but necessitates the use of a double-pole switch to disconnect both halves of the supply. The use of a PNP transistor for Q1has simply turned the circuit up-side-down however the antenna is still connected to the collector and the parallel tuned circuit is also on the collector. The circuit is turned on by the 33k on the base and the 47n keeps it rigid and turns the stage into a common base configuration. The parallel resonant circuit made up of the 8-turn inductor and 15p, starts the circuit oscillating and the 39p between collector and emitter provides feedback for the transistor to supply pulses of energy to the tuned circuit to keep it oscillating. The 220R and 39p are the emitter biasing components, as well as the 390R, 10n and 47n. The 100R and 47u are stage-separating components to remove low-frequency noise from the power rails and the 22n across the first stage tightens up the power rails as far as the high frequency is concerned and allows the low-frequency component to appear across the 3k3. The signal across this resistor is picked off via the 10k/39n combination and passed to two stages of amplification.

The 10k and 4n7 form a filter to remove high frequency pulses. A high frequency pulse will try to charge the 4n7 and most of the amplitude of the pulse will be lost (attenuated) in the 10k resistor. Exactly how this works is as follows: The high-frequency pulse will rise and fall before the 4n7 has time to charge. But a low-frequency will charge the 4n7 and enter the 39n for amplification by the rest of the circuit. Going back to the first stage, we have already mentioned that it is oscillating at 27MHz and the MOST ACTIVE lead of the circuit is the collector and this is where the antenna is connected. The waveform produced by the circuit is passed to the antenna and radiated to the surroundings.

27MHz Transmitter Circuit

2010-08-02T01:46:00.001-07:00

This is a design circuit for a simple 27MHz transmitter producing a carrier. The circuit can produces an unmodulated 27MHz signal and when picked up by a receiver. This is the figure of the circuit;

The transmitter is a very simple crystal oscillator. The heart of the circuit is the tuned circuit consisting of the primary of the transformer and a 10p capacitor. These two components oscillate when a voltage is applied to them. The frequency is adjusted by a ferrite slug in the centre of the coil until it is exactly the same as the crystal. The crystal will then maintain the frequency over a wide range of temperature and supply voltage fluctuations. The transistor is configured as a common emitter amplifier. It has a resistor on the emitter for biasing purposes but the 82p across the 390R effectively takes the emitter to the negative rail as far as the signal is concerned.

The 390R resistor prevents a high current passing through the transistor as the resistance of the transformer is very low. The tuned circuit operates at exactly the third harmonic (also called the third overtone - an overtone is a multiple of a fundamental frequency) of the crystal so that the crystal will oscillate at its third overtone (27MHz) and in-turn, keep the frequency of the circuit stable. The transformer in the collector of the transistor performs two functions. 1. It matches the impedance of the transistor to the impedance of the antenna, and 2. Creates a resonant circuit at 27MHz to make sure the crystal oscillates at this frequency.

27MHz Receiver Circuit

2010-08-02T01:45:00.001-07:00

This is a design circuit for receiver circuit that can be completed for the transmitter. The receiver is a super-regenerative design. This means it is self-oscillating (or already oscillating) and makes it very sensitive to nearby signals. It is much more sensitive than receiving a signal and making it oscillate a transistor. This is the figure of the circuit;

A super-regenerative design is not universally used because it is much more noisy than conventional reception and is not suitable for voice transmission. However it is used in simple walkie-talkies and this is why they are so noisy - as will be shown at the end of this article. When a signal of the same frequency as the super-regenerative circuit passes near the antenna, the circuit has difficulty radiating a signal. This means the circuit current VARIES. These variations appear across the 2k2 load resistor as a change in voltage and the signal is picked off via a 100n capacitor and passed to the second and third stages for amplification. The 22n across the first stage is designed to remove the high-frequency component from the waveform. If this were not present, the circuit would never change state. The receiver is tuned to the frequency of the crystal in the transmitter via a slug-tuned coil in the collector. When the transmitter is off, the receiver picks up background noise and amplifies it to produce random-noise. This is amplified by the second transistor and passed to the third via a 0.47u electrolytic. This electrolytic is designed to keep the third transistor ON for the major part of the time and it does this in a very clever way. We will assume the supply has just been turned on and the second transistor is not receiving a signal. The 0.47u will be uncharged and it will charge via the 10k collector resistor and the base-emitter junction of the third transistor.

27MHz Intercom Walkie Talkie Circuit

2010-08-02T01:44:00.001-07:00

Intercom walkie talkie are the next logical step in this discussion. They show how a crystal oscillator can be used to transmit voice. Transmitting a voice via a crystal locked oscillator is not easy. This is because the crystal is locking the frequency and it is very difficult to shift it. The only way to do it is to add the audio as an amplitude component so that the amplitude of the oscillator rises and falls with the audio signal but its frequency does not change. This is the figure of the circuit;

Nearly all the components in the 4-transistor circuit are used for both transmitting and receiving. This makes it a very economical design. The frequency-generating stage only needs the crystal to be removed and it becomes a receiver. The operation of this circuit coincides with our discussion on receiver circuits at the beginning of this article where we said the receiver was oscillating all the time, similar to a weak transmitter. A 390R is added to the emitter of the oscillator stage to reduce the activity and turn it into a receiver. The next section of the circuit is called a building block. It consists of three transistors directly coupled to produce an audio amplifier with very high gain. The first transistor is a pre-amplifier and the next two are wired as a super-alpha pair, commonly called a Darlington pair to drive the speaker transformer.

The third block is the speaker. This is a separate item because it is used as a speaker in the receive mode and a dynamic microphone in the transmit mode. A speaker can be used in reverse like this and it is called a dynamic microphone because of the coil and magnet arrangement. When you talk into the cone, the movement of the voice coil in the magnetic field produces a few millivolts output. This can be coupled to a high gain amplifier to get quite good results. When the walkie talkie is in the receive mode, the first transistor is configured as a receiver and the audio is picked off the 4k7 load resistor via a 0.47u electrolytic. It then passes through a volume control and into the three transistor amplifier. The speaker transformer couples the amplifier to the speaker and we hear the result. When the walkie talkie is in the transmit mode, the speaker is placed at the input of the audio amplifier.

Positive Low Voltage Hot Swap Controller with Power Limiter Circuit

2010-07-12T17:27:00.001-07:00

This is a design circuit of Positive Low Voltage Hot Swap Controller circuit with Power Limiter. This circuit gives intelligent control of the power supply voltage to the load during removal and insertion of circuit cards from “hot” power sources or a live system backplane. This uses The LM25069 that gives in-rush current control to limit system voltage transients and droop. This circuit has programmable current limit and power dissipation in the external series pass N-Channel MOSFET. So, operation will in the Safe Operating Area (SOA). This is the figure of the circuit;

The circuit output is used to indicate voltage is within 1.3V of the input voltage. this circuit has The programmable input under-voltage and over-voltage, programmable lockout levels and programmable hysteresis, programmable the initial insertion delay time and programmable fault detection time. The LM25069-2 automatically restarts at a fixed duty cycle, and LM25069-1 latches off after a fault detection. The LM25069 has 10 pin MSOP package. Refer to its data sheet for selecting the proper external components values that suits your need.

[Circuit Source: National Semiconductor Notes]

HYM1422 Hot Swap Controller Circuit

2010-07-12T17:26:00.001-07:00

This is a design circuit of the HYM1422 is an integrated 2.7V to 12V hot swap controller. This device allows a board to be safely inserted and removed from live back planes. This is achieved using a pass FET with a current control loop that using a sense resistor, we can monitor the input current. The board supply voltage can be ramped up at a programmable rate using an external N-channel MOSFET and capacitor. The RESET pin output can be used to generate a system reset when the supply voltage falls below a programmable voltage. The ON pin is the control input for the device and also acts as a soft reset. This is the figure of the circuit;

This device can be used in many application such as Hot-Swap/Plug/Dock Power Management, Network Switches, Routers, Hubs, and Electronic Circuit Breaker. This device also supported with many features such as provide safe hot swap for +2.7V to +12V power supplies with few external components, user-programmable supply voltage power-up rate, charge pumped gate drive for external N-FET switch, undervoltage lockout, soft reset input and glitch filter on RESET, programmable circuit breaker, and system reset output with programmable delay. This device also available in 8-pin PDIP and SOP packages.

[Schematic circuit source: Haoyu Microelectronics]

Beat Frequency Oscillator Simple Metal Detector Circuit

2010-07-12T17:24:00.002-07:00

This is a design of metal detector requires alone a scattering of apparatus and an evening’s work. Congenital about a cmos4011 IC, is actual able-bodied and versatile. The 250 kHz advertence oscillator is congenital with two gates (U1/1 and U1/2), C1, R1 and P1. The chase oscillator uses alone one aboideau (U1/3), two capacitors and the chase coil. The outputs of the two oscillators are fed to the fourth aboideau acting as a mixer and filtered with C4. This is the figure of the circuit;

After assembly, affix the headphones and boring about-face P1. The angle will get lower until it disappears. Continuing to circle P1 in the aforementioned administration will account the angle to acceleration again. The point at witch the angle is the everyman and disappears is alleged “zero beat”. If you can not get this aught exhausted abundance for the absolute about-face of P1 you may accept to worst altered ethics for C1.

Turn P1 abutting to the aught exhausted position, again move the chase braid abreast a brownish object. The accent should change, depending on the measurement and ambit of the metal. Note that this simple detector’s achievement is not commensurable to added avant-garde bartering products. It will alone ascertain about ample brownish altar at a abbreviate distance. Coins and added baby altar will be abundant harder to find!

Part List :
· U1: CD4011 (Quad 2-input NAND Gate)
· U2: LM78L05 (5V Regulator IC)
· R1: 2.2k 5% resistor
· R3: 330k 5% resistor
· R4: 270k 5% resistor
· R5: 1k 5% resistor
· C1: 390pF NPO capacitor
· C2, C3: 10nF
· C4: 100nF
· C5: 100uF/16V electrolytic
· C6: 220uF/16V electrolytic
· C7: 100nF ceramic
· P1: 4.7k lin. potentiometer
· L1: 22cm diameter, 14 turns, AWG 26
· K1: SPDT toggle switch
· J1: Headphone jack 1/4 or 1/8 inch

Audio Signal Injector/Tracer Circuit

2010-07-12T17:24:00.001-07:00

This is a circuit for testing instrument provides two alternate functions: signal injector and signal tracer. This circuit is very helpful in trouble shooting audio circuits, when you need to test a circuit by injecting a signal and observe the output (by watching the oscilloscope or by hearing the loudspeaker for example), or by tracing some points inside the circuit when an audio signal is applied to the input. This is the figure of the circuit;

This signal tracer/injector uses 9 volts supply from battery. An alligator clip is recommended for the ground probe, so you can works with one hand to hold the board, and the other hand to target the test probe. The SPDT switch connected to the transistor and the earpiece is used to select the function, whether as a signal injector or a signal tracer.

Discrete Voltage Regulator Circuit

2010-06-22T01:55:00.001-07:00

It is still possible to build circuits without IC’s and still achieve a high level of performance while integrated circuits have become a staple of all modern circuit designs. A high performance 5 volt voltage regulator built using discrete components. This is the figure of the circuit;

This circuit is not need an IC and only need to substitution a 1N4001 in lieu of a zener diode. The regulator output voltage is varies by mere 4 %. It’s also has current limiting at 1.5 amps along with short circuit protection. This circuit closely matches the performance of the 7805 5 volt regulator IC with the exception of thermal shutdown.

We can adjust this circuit as a 12 volt regulator by adjusting R4 to the desired output voltage. The input voltage must be inside the range, 18V-25. Increase resistor R1 to 2.2K for best performance if you plan to use this circuit as a 12 volt regulator. The limit of the circuit still at 1.5 amps regardless of the output voltage setting. All resistors used in this circuit are ¼ watt except for R2 which must be at least a 2 watt type or larger. In this circuit, Almost any general purpose NPN transistor can be substituted for the 2N3904 transistors used. For Q3 we can used any similar TO220 type NPN switching transistor. A zener diode can be substituted for D1 but the voltage should be at least 2 volts lower than the desired output voltage if we desired. It’s require to use of zener diode to make resistors R3 and R4 decreased accordingly.

[Circuit source: Radio Amateur Society of Norwich]

Basic Vox Circuit Controls PTT Circuit

2010-06-22T01:52:00.001-07:00

They were missing a VOX if we are take a look at some of the budget priced HF transceiver. It would certainly be nice to have VOX capability although most of these budget priced transceivers performed admirably. The figure below show us a basic VOX circuit which will perform very well once the VOX level is set correctly. This is a very low cost circuit and you can find all parts at your local Radio Shack store. This is the figure of the circuit;

The circuit below consists of the 1458 IC which is really two 741 op amps in a single package. To amplify the mike audio, we use hte first op amp. The second op amp is used as a comparator. This comparator is designed to saturate a switching transistor during periods of moderate mike audio. The necessary delay before unkeying the PTT is provided by capacitor C2 which holds a small charge when the second op amp goes high. For the particular voice or microphone being used, variable resistor R6 sets the desired VOX level and should be adjusted. We’ll need some practice if we are using a VOX circuit for the first time. Don’t use a microphone with excessive gain unless you have a very quiet household. Since the audio from the transceiver’s speaker could key the transceiver, it is also a good idea to use headphones. Increase R8 to 10K if you would like to increase the delay time. Decrease C2 to about 22uf if you would like a little less delay. Make sure that the microphone is connected to both the VOX circuit as well as to the mike input on the transceiver. Failure to do so will result in the rig being keyed without any transmitted audio. Connect the PTT to collector of Q1 in the circuit.
[Circuit source: Radio Amateur Society of Norwich]

The Big E Stereo Parabolic Microphone Circuit

2010-06-07T05:15:00.000-07:00

This is a design circuit for a stereo amplifier for a high sensitivity stereo parabolic microphone. This circuit can be used for listening to distant sounds. Typical parabolic microphones are mono phonic, this unit has a stereo audio path that helps produce more realistic sounding audio. This is the figure of the circuit.

The mini condenser microphone converts sounds into an electrical signal. Resistor R1 provides bias for the condensor microphone's internal amplifier transistor. The 2N3906 PNP transistor acts as a low noise microphone input amplifier. The 10K gain potentiometer is used for adjusting the audio signal level. A stereo 10K audio taper potentiometer can be used for adjusting both channels simultaneously, or individual 10K trimmers can be used for fixed gain applications. The preamp output signal is fed into the 1458 op-amp, which boosts the audio to a level that is sufficient for driving an 8-ohm headphone or a tape recorder input. The 1458 amplifier stage is fixed gain (10X) in the inverting configuration, it drives the headphone speakers. Capacitor C9 provides DC isolation from the 1458 op-amp output, which sits at half of the supply voltage. Resistor R13 provides impedance protection for the op-amp output and reduces audio distortion when driving low impedance headphones. DC bias for the 1458 op-amps is set at half of the supply voltage by the R16/R17 voltage divider. Capacitors C13 and C14 filter the DC power supply for the op-amp stage. The DC is further filtered for the input preamp transistors through resistor R15 and capacitor C11. Diode D1 and resistor R18 protect the circuit from reverse battery polarity.

Mobile Cell Phone Battery Charger Circuit Using 555 IC

2010-06-07T05:14:00.001-07:00

This is a design circuit for Mobile Cell phone Battery Charger. Stops charging when battery is full charged, Portable unit charging of the mobile phone, cell phone battery is a big problem while traveling as power supply source is not generally accessible. If you keep your cell phone switched on continuously, its battery will go flat within five to six hours, making the cell phone useless. This circuit is work using based on 555 IC. This is the figure of the circuit.

Generally, cell phone battery packs require 3.6-6V DC and 180-200mA current for charging. These usually contain three Ni-Cd cells, each having 1.2V rating. Current of 100mA is sufficient for charging the cell phone battery at a slow rate. A 12V battery containing eight pen cells gives sufficient current (1.8A) to charge the battery connected across the output terminals. The circuit also monitors the voltage level of the battery. It automatically cuts off the charging process when its output terminal voltage increases above the predetermined voltage level. Timer IC NE555 is used to charge and monitor the voltage level in the battery. Control voltage pin 5 of IC1 is provided with a reference voltage of 5.6V by zener diode D1. Threshold pin 6 is supplied with a voltage set by P1 and trigger pin 2 is supplied with a voltage set by P2. When the discharged cell phone battery is connected to the circuit, the voltage given to trigger pin 2 of IC1 is below 1/3Vcc and hence the flip-flop in the IC is switched on to take output pin 3 high. When the battery is fully charged, the output terminal voltage increases the voltage at pin 2 of IC1 above the trigger point threshold.

Part:

P1 = 20K

P2 = 20K

R1 = 390R

R2 = 680R

R3 = 39R-1W

R4 = 27K

R5 = 47K

R6 = 3.3K

R7 = 100R-1W

C1 = 4.7uF-25V

C2 = 0.01uF

C3 = 0.001uF

D1 = 5.6V-1W Zener

D2 = 3mm. Red LED

Q1 = SL100

S1 = On/Off Switch

B1 = 1.5vx8 AA Cells in Series

IC1 = NE555 Timer IC

Milivolt Meter Circuit Using Op Amp LM11

2010-06-07T05:12:00.000-07:00

This circuit is design for milivolt meter circuit. This circuit is using LM11. This circuit has requirements analogous to those discussed for the ammeter. This is the figure of the circuit;

In the most-sensitive position, the range resistor is zero and the input resistance equals R1. As voltage measurement is desensitized by increasing the range resistor, the input resistance is also increased, giving the maximum input resistance consistent with zero stability with the input open. Thus, at full-scale, the source will be loaded by whatever multiple of the noise current is required to give the desired open-input zero stability.

[Schematic circuit source: National Semiconductor Notes]

Bias Current Compensation Circuit Using LM11

2010-06-07T05:07:00.000-07:00

This is design circuit of bias current compensation circuit. This circuit can operate from MW source resistances with little increase in the equivalent offset voltage. This circuit is based on LM11. This is the figure of the circuit.

This is impressive considering the low initial offset voltage. The situation is much improved if the design can be configured so that the op amp sees equal resistance on the two inputs. However, this cannot be done with all circuits. Examples are integrators, sample and holds, logarithmic converters and signal-conditioning amplifiers. And even though the LM11 bias current is low, there will be those applications where it needs to be lower.

[Circuit source: National Semiconductor Notes]

Bias Current Compensation Circuit for Use with Unregulated Supplies

2010-06-07T05:03:00.000-07:00

This circuit is design for bias current compensation circuit. This circuit uses pre-regulation to solve this problem. The added reference diode has a low breakdown so that the minimum operating voltage of the op amp is unrestricted. This is the figure of the circuit;

The fact that this reference can be used for other functions should not be overlooked because a regulated voltage is frequently required in designs using op amps. This circuit is a divider is used so that the resistor feeding the compensating current to the op amp can be reduced. There will be an error current developed for any offset voltage change across R6. This should not be a problem with the LM11 because of its low offset voltage. But for tight compensation, mismatch in the temperature characteristics of R4 and R5 must be considered.

[Schematic circuit source: National Semiconductor Notes]

A Precision DC Amplifier Circuit with a 100 MHz Gain Bandwidth

2010-06-07T05:01:00.000-07:00

This is a design circuit for precision of DC amplifier circuit. This circuit has reasonable recovery

(~7 μs) from a 100% overload; but beyond that, AC coupling to the fast amplifier causes problems. This circuit is based on LM11. This is the figure of the circuit;

Alone, the gain error and thermal feedback of the LH0032 are about 20 mV, input referred, for ±10V output swing. Adding the LM11 reduces this to micro volts. An ammeter should read zero with no input current and have no voltage drop across its inputs even with full-scale deflection. Neither should spurious indications nor inaccuracy result from connecting it to low impedance. Meeting all these requirements calls for a DC amplifier, and one in which both bias current and offset voltage are controlled.

[Schematic circuit source: National Semiconductor Notes]

LM7812 using to 12V 30A Power Supply

2010-05-18T06:51:00.000-07:00

This project design is a single 7812 IC voltage regulator and multiple outboard pass transistors, this power supply can deliver output load currents of up to 30 amps. This is the figure of the circuit;

The input transformer is likely to be the most expensive part of the entire project. As an alternative, a couple of 12 Volt car batteries could be used. The input voltage to the regulator must be at least several volts higher than the output voltage (12V) so that the regulator can maintain its output. If a transformer is used, then the rectifier diodes must be capable of passing a very high peak forward current, typically 100amps or more. The 7812 IC will only pass 1 amp or less of the output current, the remainder being supplied by the outboard pass transistors. As the circuit is designed to handle loads of up to 30 amps, then six TIP2955 are wired in parallel to meet this demand.

The dissipation in each power transistor is one sixth of the total load, but adequate heat sinking is still required. Maximum load current will generate maximum dissipation, so a very large heat sink is required. In considering a heat sink, it may be a good idea to look for either a fan or water cooled heat sink. In the event that the power transistors should fail, then the regulator would have to supply full load current and would fail with catastrophic results. A 1 amp fuse in the regulators output prevents a safeguard. The 400mohm load is for test purposes only and should not be included in the final circuit.

LED Photo Sensor Circuit

2010-05-18T06:49:00.001-07:00

This is a design for sensor circuit. This circuit is using LED for sensor a light. But, for control operation and amplifier the output is using 1458 IC. This is an op-amp. This is the figure of the circuit;

A circuit that is takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light.

Infra Red Receiver Circuit

2010-05-18T06:46:00.000-07:00

Infra Red Receiver is a receiver module data through infrared wave with frequency carrier 38 kHz. This module can be functioned as input in the application of data transmission without cable like robotic, security system, data logger, absence, etc.

This is the figure of the circuit;

In doing measurement at Infra red Receiver must follow this step:

1. Connects source of tension + 5 VDC to module Infra Red Receiver.

2. Free of jumper J2.

3. Tension measure at pin OUT with voltmeter. The value will stay at logic ‘1' (around 5 V).

4. Jumper tide J2.

5. Tension measure at pin OUT with voltmeter. The value will stay at logic ‘0' (around 0 V).

6. Infrared signal berry 38 kHz (with module Infra Red Transmitter distance <>

7. Free of jumper J2.

8. Tension measure at pin OUT with voltmeter. The value will stay at logic ‘0' (around 0 V).

9. Jumper tide J2.

10. Tension measure at pin OUT with voltmeter. The value will stay at logic ‘1' (around 5 V).

50 W Amplifier Circuit Using Transistor

2010-05-18T06:44:00.000-07:00

This is a design of circuit that is very rugged and reasonably power amplifier circuit that can be used for any audio applications. The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values. This is makes it ideal to assemble from your electronics junk box. This is the figure of the circuit for the amplifier;

The operation of the amplifier is the amplifier produces 60W rms at 50V supply on a 8 Ohm load. The capacitor C1 controls low frequencies and capacitor C2 controls high frequencies. The circuit is basically a class B amplifier. The transistors 2N 3055 serves the function of driving the speaker. The other transistor functions as pre amplifiers for the driver stage. This is the basic scheme of the circuit. The maximum power level of amplifier can be set by adjusting the 500 Ohm POT connected with the BC107 transistor.

The are some notes for this circuit. The circuit can be powered using a 50 V DC power supply with 5A current rating. It is up to 60 V can be given to the circuit. Any way the power supply must be well regulated and filters to avoid noise. The amplifier is adjusts the 500 ohm POT to obtain optimum performance. Volume control can be attained by connecting a 10 K POT in series to the input of the amplifier.

Temperature Monitor for Microprocessor Systems Circuit

2010-05-14T06:01:00.000-07:00

This is a design circuit for monitoring the temperature. This circuit is used an NE1617A. This is the figure of the circuit;

RGB/White/Blue 8-LED Fun Light Driver Circuit From The Power Wise Family

2010-05-14T05:59:00.001-07:00

LP3944 is an integrated device capable of independently driving 8 LEDs. This device also contains an internal precision oscillator that provides all the necessary timing required for driving each LED. Two prescaler registers along with two PWM registers provide a versatile duty cycle control. The LP3944 contains the ability to dim LEDs in SMBUS/I2C applications where it is required to cut down on bus traffic. This is the figure of the circuit;

Traditionally, to dim LEDs using a serial shift register such as 74LS594/5 would require a large amount of traffic to be on the serial bus. LP3944 instead requires only the setup of the frequency and duty cycle for each output pin. From then on, only a single command from the host is required to turn each individual open drain output ON, OFF, or to cycle a programmed frequency and duty cycle. Maximum output sink current is 25 mA per pin and 200 mA per package. Any ports not used for controlling the LEDs can be used for general purpose input/output expansion.

[Schematic circuit source: National Semiconductor Notes]

Fully Differential, Mono, Ceramic Speaker Driver Circuit

2010-05-14T05:57:00.001-07:00

This is a design circuit for speaker driver circuit. This circuit is based on LM48556 as controller the circuit. This is the figure of the circuit;

The LM48556 is a single supply, mono, ceramic speaker driver with an integrated charge-pump, designed for portable devices, such as cell phones, where board space is at a premium. The LM48556 charge pump allows the device to deliver 17.5VPP (typ) from a single 4.5V supply. Additionally, the charge pump features a soft start function that minimizes transient current during power-up.

The LM48556 features high power supply rejection ratio (PSRR) of 80dB at 217Hz, allowing the device to operate in noisy environments without additional power supply conditioning. Flexible power supply requirements allow operation from 2.7V to 5.0V. Additionally, the LM48556 features a differential input function and an externally configurable gain. A low power shutdown mode reduces supply current consumption to 0.1μA.

Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. The LM48556 is available in an ultra-small 12-bump micro SMD package (2mm x 1.5mm).

[Schematic circuit source: National Semiconductor Notes]

3 W Mono Class-D Audio Power Amplifier Circuit

2010-05-14T05:54:00.000-07:00

This is a design circuit for audio power amplifier. This circuit uses SA58672 as main controller in this circuit. This is the figure of the circuit;

The SA58672 is a mono, filter-free class-D audio amplifier which is available in a 9 bump WLCSP (Wafer Level Chip-Size Package) and 10-terminal HVSON packages. The SA58672 features shutdown control. Improved immunity to noise and RF rectification is increased by high PSRR and differential circuit topology. Fast start-up time and very small WLCSP package makes it an ideal choice for both cellular handsets and PDAs. The SA58672 delivers 1.7 W at 5 V and 800 mW at 3.6 V into 8 W. It delivers 3.0 W at 5 V and 1.6 W at 3.6 V into 4 W. The maximum power efficiency is excellent at 90 % into 8 W and 84 % to 88 % into 4 W. The SA58672 provides thermal and short-circuit shutdown protection.

[Circuit source: NXP Semiconductor Notes]

Wide Voltage Range 1.8 Watt Audio Power Amplifier Circuit with Short Circuit Protection

2010-05-07T06:39:00.000-07:00

This is a design circuit for power amplifier using wide voltage range. This circuit is based on LM4951 single op-amp circuit. This is the figure of the circuit;

The LM4951A is an audio power amplifier designed for applications with supply voltages ranging from 2.7V up to 9V. The LM4951A is capable of delivering 1.8W continuous average power with less than 1% THD+N into a bridge connected 8Ω load when operating from a 7.5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4951A does not require bootstrap capacitors, or snubber circuits. The LM4951A features a low-power consumption active-low shutdown mode. Additionally, the LM4951A features an internal thermal shutdown protection mechanism and short circuit protection.

The LM4951A contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4951A is unity-gain stable and can be configured by external gain-setting resistors.

[Schematic circuit source: National Semiconductor Notes]

Low Voltage Mixer FM IF Circuit Using SA58640 Single Chip IC

2010-05-07T06:36:00.000-07:00

This is a design circuit for FM mixer circuit with low voltage. This circuit is based on SA58640 single chip IC from Phillips semiconductor. This circuit can produce 45 MHz frequency for mixing the FM signal. This is the figure of the circuit;

For testing this circuit, we can use and follow the setting tester. The C-message and de-emphasis filter combination has a peak gain of 10 for accurate measurements. Without the gain, the measurements may be affected by the noise of the scope and HP339A analyzer. The de-emphasis filter has a fixed -6 dB/Octave slope between 300 Hz and 3 kHz. The ceramic filters can be 30 kHz SFG455A3s made by Murata which have 30 kHz IF bandwidth (they come in blue), or 16 kHz CFU455Ds, also made by Murata (they come in black). All specifications and testing are done with the wideband filter. Set your RF generator at 45.000 MHz, use a 1 kHz modulation frequency and a 6 kHz deviation if you use 16 kHz filters, or 8 kHz if you use 30 kHz filters. The measured typical sensitivity for 12 dB SINAD should be 0.45 mV or -114 dBm at the RF input. The smallest RSSI voltage (i.e., when no RF input is present and the input is terminated) is a measure of the quality of the layout and design. If the lowest RSSI voltage is 500 mV or higher, it means the receiver is in regenerative mode.

In that case, the receiver sensitivity will be worse than expected. All of the inductors, the quad tank, and their shield must be grounded. A 10 mF to 15 mF or higher value tantalum capacitor on the supply line is essential. A low frequency ESR screening test on this capacitor will ensure consistent good sensitivity in production. A 0.1 mF bypass capacitor on the supply pin VCC, and grounded near the 44.545 MHz oscillator improves sensitivity by 2 dB to 3 dB. R5 can be used to bias the oscillator transistor at a higher current for operation above 45 MHz. Recommended value is 22 kW, but should not be below 10 kW.

[Schematic project circuit source: Phillips Semiconductor Notes]

High-Performance 56W Audio Power Amplifier Circuit with Mute

2010-05-07T06:34:00.001-07:00

This is a circuit schematic for basic design of power amplifier circuit. This circuit is based on LM3876 as a controller and op amp this circuit. This is the figure of the circuit;

The LM3876 is a high-performance audio power amplifier capable of delivering 56W of continuous average power to an 8 load with 0.1% THD+N from 20Hz-20kHz. The performance of the LM3876, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, under-voltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks. The LM3876 maintains an excellent signal-to-noise ratio of greater than 95dB (min) with a typical low noise floor of 2.0µV. It exhibits extremely low THD+N values of 0.06% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

[Circuit schematic source: National Semiconductor Notes]

Digital Temperature Sensor and Thermal Watchdog Circuit

2010-05-07T06:31:00.000-07:00

The LM75A uses the on-chip band gap sensor to measure the device temperature with the resolution of 0.125 °C and stores the 11-bit 2's complement digital data, resulted from 11-bit A-to-D conversion, into the device Temp register. This is a figure of block diagram for the circuit of digital temperature sensor;

The device can be set to operate in either mode: normal or shutdown. In normal operation mode, the temp-to-digital conversion is executed every 100 ms and the Temp register is updated at the end of each conversion. In shutdown mode, the device becomes idle, data conversion is disabled and the Temp register holds the latest result; however, the device I2C-bus interface is still active and register write/read operation can be performed. The device operation mode is controllable by programming bit B0 of the configuration register. The temperature conversion is initiated when the device is powered-up or put back into normal mode from shutdown.

In addition, at the end of each conversion in normal mode, the temperature data (or Temp) in the Temp register is automatically compared with the over-temperature shutdown threshold data (or Tos) stored in the Tos register, and the hysteresis data (or Thyst) stored in the Thyst register, in order to set the state of the device OS output accordingly. The device Tos and Thyst registers are write/read capable, and both operate with 9-bit 2's complement digital data. To match with this 9-bit operation, the Temp register uses only the 9 MSB bits of its 11-bit data for the comparison.

[Schematic circuit source: NXP Semiconductor Notes]

Voltage And Current Noise Tester Circuit

2010-03-31T23:12:00.000-07:00

This is a simple design circuit for tester circuit. This circuit is based on LM791. This is the figure of the circuit.

Using large resistor value make the current noise dominate since it is coupled into the resistance and thus voltage noise and thermal noise become negligible compared to the current noise. The output voltage is specified as Vout and input voltage as Vin and box noise enabled is checked.

[Schematic circuit source: National Semiconductor Notes]

Single Television Conversion Terrestrial Tuner Evaluation IC Circuit

2010-03-31T23:07:00.000-07:00

This is a design circuit for conversion tuner. This circuit is based on MAX3540 single chip IC. This is the figure of the circuit.

This television tuner draws only 760mW of power from a +3.3V supply voltage. The MAX3540 is designed to convert NTSC or ATSC signals in the 54MHz to 860MHz band to a 44MHz intermediate frequency (IF). The MAX3540 includes a variable-gain low-noise amplifier, multi band tracking filters, a harmonic-rejection mixer, a low-noise IF amplifier, an IF power detector, and a variable-gain IF amplifier. The MAX3540 also includes fully-monolithic VCOs and tank circuits, as well as, a complete frequency synthesizer. This highly integrated design allows for low-power tuner-on-board applications without the cost and power-dissipation issues of dual-conversion tuner solutions. The MAX3540 is specified for operation in the 0°C to +85°C temperature range, and is available in a leadless 48-pin flip-chip (fcLGA) package.

[Schematic circuit source: MAXIM Application Notes]

RF Power Amp Bias Circuit

2010-03-31T23:00:00.000-07:00

This is a design circuit for power amps bias circuit. This circuit can be used to temperature compensate the gate voltage of an LDMOS. The output voltage of this circuit is equal to twice the DS4303's VOUT plus the PNP's VBE. The doubled DS4303 voltage is a low temperature-coefficient voltage source. The PNP's VBE will change approximately +2mV/°C, providing temperature compensation for the LDMOS. This circuit can provide good temperature compensation for the LDMOS, assuming that the PNP is thermally coupled to the LDMOS. This is the figure of the circuit;

This circuit is based on LDMOS DS4303 from MAXIM. To calibrate this circuit, place the expected DS4303 output voltage on the VIN pin, and pull the Adjust signal low to trigger the DS4303 to update its output voltage. Once the DS4303 completes its update, measure the quiescent current using the current sense amplifier, and iterate until the proper bias is reached. The input to the DS4303 should be held static while it is converging to ensure it reaches the proper value.

[Circuit schematic source: MAXIM Application Notes]

Open Loop And Phase Test Circuit

2010-03-31T22:57:00.000-07:00

This is the simple design circuit for test circuit. This circuit is based on LM791 for control the operation. This is the figure of the circuit;

When testing the open loop and phase, the user should choose an upper frequency limit that goes beyond the unity gain bandwidth of the amplifier. The capacitor is chosen to be large to provide roll off (f=1/2 πR1C2) so that even if the op amp tested has very low frequency dominant pole, the simulation shown a smooth transition and 20 dB per decade roll off.

[Circuit source: National Semiconductor Notes]

Line Driver Power Supply Circuit

2010-03-29T13:11:00.000-07:00

This is a design circuit for power supply that based on LM1578 single chip IC. The LM1578A Switching Regulator can be used to convert the already existing supply into a separate ±12V supply for powering the interface line drivers. This is the figure of the circuit.

The power supply, shown in the figure operates from an input voltage as low as 4.2V, and delivers an output of ±12V at ±40 mA with an efficiency of better than 70%. The circuit provides a load regulation of ±1.25% (from 10% to 100% of full load) and a line regulation of ±0.08%. Other notable features include a cycle-by-cycle current limit and an output voltage ripple of less than 40 mVp-p. A unique feature of this flyback regulator is its use of feedback from BOTH outputs. This dual feedback configuration results in a sharing of the output voltage regulation by each output so that one output is not left unregulated as in single feedback systems. In addition, since both sides are regulated, it is not necessary to use a linear regulator for output regulation.

[Schematic circuit source: National Semiconductor Notes]

Classic Thermistor Based Discrete Temperature Sensor Circuit

2010-03-29T13:07:00.000-07:00

This is a design circuit for discrete-component circuits for both continuous temperature measurement and over-temperature alarm indication have traditionally used a thermal-resistor (thermistor) for a sensor element. This circuit is based on LM75 from National Semiconductor. This is the figure of the circuit;

The most commonly used thermistor is a negative-temperature-coefficient (NTC) thermistor; as temperature increases, the resistance of the NTC thermistor decreases. For a system processor to utilize the temperature information from a thermistor, the temperature-to-resistance parameter is generally converted to a temperature-to-voltage signal. The analog temperature signal is derived directly from the voltage divider, producing a voltage level that is an analog of the thermistor's temperature (VTEMP). The RBIAS1 resistor is necessary to set the gain of the circuit and to keep the thermistor operating within its optimal power dissipation, which minimizes temperature-induced error in the resistance. The over-temperature alarm (TOVER) is generated by connecting the output of the thermistor to the input of the comparator in order to set the voltage (over-temperature level) at which the comparator output is to go active. A hysteresis feedback loop is included to keep the comparator from rapidly switching back and forth when VTEMP is equal to the VREF.

[Schematic circuit source: National Semiconductor Notes]

Typical Flyback Circuit

2010-03-24T22:24:00.000-07:00

This is a design circuit for flyback circuit. This flyback mostly found in a direct view color television or computer monitor. The right side show us the high voltage section. This section consist of HV to CRT, focus, and screen divider network. On monochrome an black-and-white TV, the flyback transformer do not have screen divider and focus. This is the figure of the circuit.

The flyback have a ferrite core that constructed with precision gap that mostly made from pieces of tape or plastic spacer. For focus and screen divider we use a potentiometer and resistor with value 10s to 100s M ohm. D1 to D3 are used to rectify the high voltage that will read open on typical DMM or VOM.

SA58672 Small Class-D Audio Amplifier Circuit for Mobile Device

2010-03-24T22:20:00.000-07:00

This is a circuit of SA58672 Small Class-D Audio Amplifier. This circuit is suitable for mobile device. It has maximum output power of 3.0 W for a 4ohm load and 1.7W for 8ohm load with power supply of 5V. If we uses 3.6 V power supply, the maximum output power is 900mW with 8ohm load. This is the figure of the circuit;

Using 9-bump Wafer Level Chip Scale Package (WLCSP), the SA58672UK save space in portable designs, because it measures only 1.66 x 1.71 x 0.6 mm.

This circuit produces better overall audio performance because it has improved RF rectification and immunity to noise. The SA58672UK is suitable for cellular handsets or wireless and other portable audio application because it has fast start-up time of 7 ms eliminates pop-on sounds.

[Schematic diagram source: NXP Application Note]

Provide Remote Alarm Circuit for Smoke Detector

2010-03-24T22:13:00.000-07:00

Ionization-based smoke detectors are efficient and cheap, so they are often installed in the house, other outbuildings, and the garage. The Locations of the device is far from house, so we need to transmit the alarm signals back into central home-security system or the house. This is a simple circuit that sense a supply current increase because activation of smoke detector’s internal alarm triggers it. Then this circuit will send a remote output to central security system or main dwelling to sound the alarm. This is the figure of the circuit.

This circuit uses The MAX921 as comparator, because it has low supply current, internal voltage reference, and wide supply-voltage range. During monitor mode, the typical value of currents are 50µA and when the sounder is active, the current values are 3mA. This circuit receives power from the smoke detector’s battery. The output of this circuit is an open-drain FET, it can trigger an RF module that communicates or drive the home-security system back to the residence. When the alarm is active, the voltage across the sense resistor is greater than 30mV. So the circuit trip point is set at 18mV. The hysteresis pin is connected for minimum hysteresis in the comparator, because the difference voltage between inactive and active operation is so great. To prevent false triggers, this circuit uses capacitor that will reducing the sensitivity to RF noise and noise.

[Circuit schematic source: maxim-ic.com]

High Performance Sawtooth Generator Circuit

2010-03-24T22:09:00.000-07:00

This is a design for sawtooth generator circuit. The advantage of this circuit is low cost and produces an auxiliary square wave at the same frequency. This circuit can be used to sweep the frequency of another generator. This is the figure of the circuit.

A voltage-controlled current source is formed by IC1 with R1 and Q1. The C1 is discharged by current Io until it’s voltage is less than 1.66V. It will swing its output to 5V and trips the IC2A comparator. The C1 is charged by current through the diode-connected transistor (Q2) until its voltage reaches 3.33V, so the IC2A output to swing back to ground. The output frequency is determined by :

fOUT = (3(5V +VC)/5V)(1/R1C1).

We can set the fOUT as high as desired by adjusting the values of C1and R1, subject to the limitations of comparator IC2A’s slew settling and rate time. The frequency range over which it can operate determined by generator’s linearity.

AC Mode Universal Motor Drive

2010-03-24T22:04:00.000-07:00

This is a design circuit for AC mode universal motor drive circuit that is suitable for large range of application. It uses the microcontroller to interpret the user interface that is used to select the four operating modes that are defined in hardware. This is the figure of the circuit.

As power switch, this circuit use “SNUBBERLESS” TRIAC BTA 12-600BW with a maximum specified gate trigger current of 50mA at 25°C. It is driven by pulse. A small signal transistor interfaces the “SNUBBERLESS” TRIAC and the microcontroller. If spurious triggering is prohibited in case of mains perturbation we should implement a small filter RfCf, although no snubber is needed in nominal operations. For synchronization, this circuit uses zero voltage detection across the mains. We can change operation from 50Hz to 60Hz by changing the EPROM/ROM table defining TRIAC conduction angle versus power level. It can be self-adapted by software or hardware programmed.

[Circuit schematic source: STMicroelectronics Application Note].