Simple Proximity Detector

How to make a simple Proximity detector or sensor


This is a simple proximity detector using IC CS209. The CS209A is a bipolar monolithic integrated circuit for use in metal detection/proximity sensing applications.The CS209A contains an oscillator set up by an external parallel resonant tank and a feedback resistor connected between pin 2 & 3 .The internal oscillator operates close to the resonant frequency of the tank circuit.As a metal object is brought close to the inductor, the amplitude of the voltage across the tank gradually begins to drop. When the envelope of the oscillation reaches a certain level, the IC causes the outputs to toggle states.potentiometer connected between pin 1 & 8 is adjusted to achieve a certain detection distance range. The larger the resistance the greater the trip-point distance.Detection range can be increased by using a high Q coil.Maximum possible range is 1 inch with a  well tuned  circuit.Only difficulty in making this  circuit is the tuning up the circuit to a particular range.For making it easy place a metal piece at the desired distance from coil (with in 1 inch) and adjust resistance Rf to make one of the outputs (  pin4 or 5) to change state.

Proximity Detector Circuit Diagram

Simple Proximity Sensor

Simple Proximity Detector Circuit

We have more related circuits in Proximity Detectors , Take a look below:

1. Magnetic Proximity Switch

2. Low Cost Fire Alarm Circuit


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11 thoughts on “Simple Proximity Detector

  1. shobi

    hmmmmm……. nyc……. i was just looking for this… how can we increase the proximity more than one inch……?? 🙂

  2. s.h.reddy

    Some i tried here in bangalore for the IC CS209a but in vain. can any body help me where i can get it.
    my mail id

  3. Dave collins

    Hi could this application be used to activate a cat flap type lock? would it detect a metal bell on the cats collar.
    Thanks Dave


    thank you for sharing your adea about this proximity detector. it have a great use to me in getting reed of burglars.

  5. mohammad

    hello. I have need to metal(gold) detector circuit .
    please… send schematic . very very tanx . i live in iran .


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