The low frequency indicates that your fingers are not so moist and salty, because your body condition is normal and not in a stressful condition.Ī very simple yet effective electronic fishing lure circuit can be seen in the following diagram, which is actually a simple piezo buzzer circuit, effectively applied as an electronic fishing lure or a fishing aid circuit R1 = 68k, R2 = 10k, T1 = BC547, L1= standard buzzer coil, PZ = 27mm piezo element When you press your two fingers across the blue pads, and switch ON power, the speaker starts producing a low frequency sound. The simple lie detector circuit will surprise you by its fairly accurate results. When the IC1 output decreases, the IC2 output increases causing a positive defection on the meter. When the magnetic field is detected by the hall effet sensor, the IC1 output rises, causing a proportionate decrease across the IC2 output, which in turn generates a negative indication on the meter. In the standby mode, the two points happen to be with exactly the same voltage levels, displaying 0 voltage over the meter. Therefore ME1 picks up the voltage difference across the two. Meter ME1 is hooked up across the IC2 output and this particular voltage divider. The resistive divider created through resistors R5 and R6 in the same way generates an output of 1 / 2 the supply voltage. This generates 1 / 2 the supply voltage on the IC2 output. This subsequent voltage are adjustable by means of potentiometer VR 1, and practically it can be tweaked to generate a voltage that will have the exact normal output voltage through hall effect IC1 probe. Opamp 1C2 boosts the voltage difference between the input voltage and the R1 and the voltage at its non-inverting input (pin 3). Increased voltage gain might naturally delivers improved sensitivity, however it might as well have its own complications due to noise and deviations. This breaks down to at slightly above 300 for the present design. Actually, it can be more than 100,000 times for any standard opamp.Īpplying negative feedback minimizes the design's voltage gain in general into a considerably more workable magnitude, and this "closed loop" gain is equivalent to the value of R4/R1. The built-in voltage gain of IC2, or the "open loop" gain as it is actually called, is incredibly large at DC voltages, and lower frequencies. The op amp is configured in an inverting mode circuit, that includes resistors R1 and R4 positioned as negative feedback link. IC1 is the Hall effect sensor and 1C2 is a precision opamp IC2 rigged to deliver a bit of extra amplification. The complete circuit schematic for the proposed Magnetic Field Detector presents itself in the following figure.
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