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Monday, July 12, 2010

Beat Frequency Oscillator Simple Metal Detector Circuit

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


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