How to Make a Simple Metal Detector Circuit Using IC CS209A

The principle of operation of the proposed metal detector circuit is quite basic yet very interesting. The detecting function is triggered by sensing the decrease in the Q level of the LC network associated with the circuit in the presence of a metal at a specified proximity level. Basically the built-in oscillator of the IC CS209 is made function
 How to Make a Simple Metal Detector Circuit Using IC CS209A - schematic

al with the inclusion of a parallel resonant LC tuned network in conjunction with a feedback resistor wired up with the OSC and RF pin outs. The impedance of the tuned resonant network may be expected at the maximum level as long as the driving source frequency is equal to the resonant frequency of the LC circuit network. On detecting the presence of a metallic object at a close proximity to the inductor sensor, the voltage amplitude of the LC network gradually begins to fall corresponding to the closeness of the metal to the inductor. Due to the above factor when the oscillation frame of the chip drops and reaches a certain threshold level, triggers the position of the complementary outputs such that they change states. Referring to the figure, as soon as a metal object is detected at the inductor input, the capacitor connected to the DEMOD gets charged through an in built current source of 30 uA. However during the detection process the above current gets deviated away from the capacitor proportionately with the generated negative bias on the LC network. This resulting reference level then equals near about 1. 2 volts which introduces some sort hysteresis in the circuit, and becomes ideally suited for preventing wrong or false triggering. Position a metal object at relatively larger distance away from the inductor, assuming the Q of the LC to be at the maximum sensitivity and the distance to be within the allowable range...

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