Simple Proximity Detector

jacky October 17, 2018 11 Comments

In this project, let’s learn how to make a Simple Proximity Detector or Sensor circuit using minimal components. A proximity detector is a fun project with lots of interesting applications to be built with. You can make very useful applications like a burglar alarm, a visitors counter, a proximity based switching application etc. This is a pretty conventional circuit designed using digital IC CS209 which has been in use for so long. In recent times, proximity based applications are developed using PIR sensors – which are available at cheap prices now.

DIY – Simple Proximity Detector

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

  • June 25, 2012

    i read the circuit now so i test this circuit working good then i will tell

  • shobi
    January 24, 2011

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

  • seetharaman
    July 29, 2010

    Hi Reddy this chip is obsolete and no more available and there is no equivallent also.
    you may try the following link

  • s.h.reddy
    July 28, 2010

    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

  • May 18, 2010

    pls. send me gold detector diagram which is applicable or intended to philippine condition

  • Dave collins
    November 23, 2009

    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

    • admin
      December 10, 2009

      I am not sure. We need to experiment.

  • Dhanashree
    August 13, 2009

    hello, i need a simple opamp741 circuit that i can make for a college project please reply on

    April 7, 2009

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

  • mohammad
    March 20, 2009

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

    • admin
      April 5, 2009

      there are many metal detector circuits in the site itself.pls have a look

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