Inductive sensors work based on two very important phenomenon viz. resonance and eddy currents. The following figure presents a block diagram of a commercial inductive proximity switch.


The coil and the oscillator are at the heart of the inductive sensor. The oscillator is commonly a RLC resonance circuit. As a metallic target is moved towards the detection coil the amplitude of the oscillations in the coil begins to decrease, since eddy currents are setup in the target, which load the coil. This is detected by the trigger circuit and it sends a signal to the output block that a target has been detected. A schematic of a very crude proximity switch is presented in the figure below.


As a target is brought near inductor L1 the amplitude of the oscillations decreases, which is detected by a Teensyduino that switches on a LED.



6 thoughts on “A DIY Crude Inductive proximity switch

  1. Hi,
    I’m interested in building my own inductive proximity detector.
    Did you use the Teensyduino to provide the square wave for the oscillator? Then feed the output from the diode envelope detector back into the Teensyduino?

  2. Hi,
    Yes, square wave is fed from the Teensyduino. You can have a look here for a better solution with a more predictable behaviour.

    Click to access CD00178756.pdf

    Finally, the best / simple solution could be to get a dedicated IC to do the job like the LMP91300 … maybe.

  3. Could you give the code and which software is being used to check waveforms ? And what to do to increase the range ?

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