How to Build a Rheostat

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

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.

Tone/Frequency Detector Circuit

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

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.

Flame Detector Circuit

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.

LED Photo Sensor Circuit

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

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).

Digital Temperature Sensor and Thermal Watchdog Circuit

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]

Classic Thermistor Based Discrete Temperature Sensor Circuit

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]

Provide Remote Alarm Circuit for Smoke Detector

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]

Power-Fail and Low-Line Signals Circuit

This is a design circuit of Power-Fail and Low-Line Signals. This circuit is used to warn the processor when the power failure or a brownout is occurs. The processor will enter a power-down routine, when either of those signals interrupts the processor. Back up important data prior to the POR placing the processor in reset and cease its current activities are things that the processor will do when enter the routine. This is the figure of the circuit.


Power-fail comparator is used to create a power-fail signal by monitoring the unregulated DC voltage. The regulator powers both supervisor circuit and the processor by using the unregulated DC voltage. The regulator’s output capacitor retains its output voltage, so the unregulated voltage drops before the regulator’s voltage. And also, we can know drop in the regulator’s voltage. The processor can enter its power-down routine prior to being reset, if the power supply voltage were to drop low enough because of Detecting the regulator’s voltage drop.
A supervisor provides a low-line signal, which goes active whenever the monitored power supply drops to a level slightly above the reset threshold so the processor can still receive warning of an imminent power failure when there is no access to the unregulated voltage. To cause the POR to issue a reset, the processor warned that the power supply voltage may decrease enough by the low-line signal. To anticipate the POR generating a reset, the processor backs up important data because of power failure or a brownout. [Circuit Schematic Source: maxim-ic.com]

IR Linked Temperature Sensor Circuit Using Maxim Single Chip IC

This is a design circuit that can be used transmits temperature data over an IR link and it allows the isolation of temperature sensor. It is a good solution of obtaining temperature readings from points at potentials a few tens of volts from ground by linking a temperature probe only by an IR connection to the readout point. This circuit is consists of a temperature sensor, an IR receiver, and an IR transmitter. This is the figure of the circuit.


As the temperature sensor, this circuit uses the MAX6576 that will convert temperature into period. This sensor is connected to the IR transmitter. The IR transmitter is triggered to generate a short (about 10µs), high-intensity IR pulse by each positive-going transition of the square-wave output from the MAX8576. This circuit also uses a 74HC132, the three fourth gates are paralleled and used as the IR LED driver and the remaining one gate is used as a positive edge differentiator. This circuit powered by a CR3032 lithium battery. The second circuit is a IR Receiver/Signal Processor that is used to receive the IR light pulses generated by the temperature sensor. It will transform the IR light pulses into two types of output: analog and digital. The analog output is a DC voltage proportional to the IR signal period and the digital output is simply a standard logic pulse recovered from the IR signal. This circuit consist of four circuit block: the signal-recovery/timing generator, the linear ramp generator, the buffered sample-and-hold and the amplifier/filter. [Circuit schematic source: Maxim Notes]

AF-RF Signal Detector Circuit

This is a design circuit for sensing the signal AF or RF. This circuit is very easy to built and is cheaper cost. This circuit is work with based TDA2822. Basis using a series of audio amplifier and loudspeaker to the input signal to switch to the AF and RF. The entire device can be made small so that it can be inserted in the vessel to maintain security. Here’s the circuit schematic diagram.


Audio amplifier section in this series created by IC TDA 2822M, with a low power stereo amplifier in 8-pin mini-DIP. IC is used as a bridge configuration to minimize the output power up to 250 MW, the loudspeaker is in use 4 ohm, 500mW. Cash needed less than 10mA with a 3V battery voltage. When the position switch is in selector AF, signal audio input is working on the input AF amplifier (IC 1 pin 7) through the capacitor C2 and Potentiometer VR1. Capacitor C2 is always holding of the input DC voltage from the amplifier and built in the audio frequency signal. Input signal IC 1 can be arranged with the help potentiometer VR1.

When the selector switch on the RF position, a series of detector and demodulator formed by capacitor C1, diode D1, and resistor R1 and R2 which are connected to the input circuit. When the audio signal is detected it will be significantly strengthened to enter the circuit. For sensing the signal is done with the touch (Probe) in the foot-foot component that is.

LED Current Sense Circuit

This is a design circuit for the physical implementation of the LED current sense circuitry assuming the thermal fold back circuitry is a simple current source. This circuit is based on the LM3424 uses an external current sense resistor (RSNS) placed in series with the LED load to convert the LED current (ILED) into a voltage (VSNS). This is the figure of the circuit.


The HSP and HSN pins are the inputs to the high-side sense amplifier which are forced to be equal potential (VHSP=VHSN) through negative feedback. For matching and noise performance, the suggested signal current ICSH is approximately 100 μA. This current does not flow in the LEDs and will not affect either the off-state LED current or the regulated LED current. ICSH can be above or below this value, but the high-side amplifier offset characteristics may be affected slightly. [Schematic’s circuit source: National Semiconductor, Inc]

Light Sensor Circuit

This is a design sensor circuit that can be used for sensing the light. This circuit is using a comparator LM311. This circuit is very simple design. This is the figure of the circuit.


This comparator is powered from 12 V DC supply and does not require negative supply to work efficiently. Feedback given to the comparator provides some hysteresis and the potentiometer allows to adjustment the sensitivity of the detector for darkness.

Part:
R1 = 1K
R2 = 100K
R3 = 10K
R4 = 2K
D1 = PHOTODIODE
D2 = 1N4001
K1 = RELAY SPDT
U1 = LM311

RTD Current Excitation Circuit

This is a RTD sensing element requires astable current reference for excitation. In this voltage reference, along with two operational amplifiers, are used to generate a floating 1 mA current source. This is the figure of the circuit.


This is accomplished as follows. The op amp A1 and the resistors R1 through R4 form a difference amplifier with a differential gain (GA1) of 1 V/V (since the resistors are all equal). A 2.5V precision voltage reference (VREF) is applied to the input of this difference amplifier. The output of op amp A2 (VOUT2 ≈ V2) serves as the difference amplifier’s reference voltage.

Infra Red Link Circuit

This is a battery powered IR Link which may be used in more than one room. This circuit is built by CMOS IC and transistor. This is the figure of the circuit.


This circuit is not powered directly from the battery. When a remote control signal is received, the energy stored in C2 drives the emitter diode. At the same time, Q1 switches on briefly to allow the battery to recharge C2. The green LED shows that the circuit is transmitting; and the yellow LED confirms that C2 has been topped-up. There is unwanted IR radiation in both daylight and tungsten lighting. To minimize its effect use an opaque housing and do not make the opening too large. (Try a horizontal slot measuring 2 cm X 1.5 cm.) Shade the receiver diodes by mounting them side-by-side a few centimeters deep, inside the case. The depth of shading required will depend on the lighting conditions. When the source of the unwanted radiation is removed the unit may be reset by interrupting the power supply for a few seconds or by pushing the (optional) reset button. If you do neither then it will reset itself after about an hour when C2 has recharged through R7.

Precision Half Wave Peak Detector Circuit

This is a simple circuit for half peak detector. The circuit is using transistor. This circuit is very compact and low cost, but if the application require precise detection for signal under 100mV then that circuit is become useless. In the figure below, the circuit is become precise half-wave peak detector circuit using only a single op-amp with few passive components. This is the figure of the circuit.


This peak detector circuit can be implemented both for average peak detector or a fast peak detector by selecting R2 and R3 values as shown in the table. Note that the output impedance is set by R3, so make sure that the output of this peak detector circuit will be connected to a higher impedance input stage. [Schematic diagram source: National Semiconductor Application Note]

Light Sensor Circuit Using PIC16C63

This light sensor circuit that is photos sensor is the gap between light and electronics. This circuit is built by op amp and microcontroller PIC16C63 for control the sensor. This circuit is not precision application, but they can be effectively used in position photo sensing applications minus the headaches of amplifier stability. This is the figure of the circuit.


When the two, six or eight channel PGA is used in this system, the other channels can be used for other sensors or an array of photo sensors without an increase in signal conditioning hardware or PIC micro® microcontroller I/O pin consumption. The multiplexer and high-speed conversion response of the PGA / Analog-to-Digital (A/D) conversion allows the photo sensor input signal to be sampled and quickly converted to the digital domain. Switching from channel to channel is then easier with the Serial Peripheral Interface (SPI) from the PIC16C63 microcontroller to the PGA. The PGA can be configured with a photo sensor in two different settings. These circuits are appropriate for signal responses from DC to ~100 KHz. [Schematic circuit source: Microchip Technology, Inc]

Tiny Temperature Sensor Circuit

This is a circuit for sensing the temperature. This circuit is simple form circuit of the temperature sensor. This circuit is built by op amp LM20, ADC. This is the figure of the circuit.


Basic fro the figure, the output voltage is transfer function of various analog output temperature sensors. These sensors are available in tiny packages like the SC70 and the 4-bump micro SMD. The LM20 is the smallest, lowest power (10μA max) analog output temperature sensor from National Semiconductor, Inc has released and is available in the SC70 and micro SMD packages. The LM70 and LM74 are MICROWIRE/SPI compatible digital temperature sensors and are available in the LLP and 8-bump micro SMD packages, respectively. The LM70 and LM74 have resolutions of 0.125°C and 0.0625°C, respectively. The LM74 is the most accurate of the two, with an accuracy of better than ±1.25°C.