Proximity Sensor With 2N7000 Mosfet


Introduction: Proximity Sensor With 2N7000 Mosfet

About: Music: my profession for over 40 years... Electronics: my beloved hobby always.

FET Proximity Sensor

This very simple proximity detector circuit will sense over 1 meter range with very few components. Output can be modified to drive a relay, power transistor or mosfet .

Step 1: For Maximum Sensitivity, R2 Should Be of a Large Value ( in the 1000 Mohm Range ) . You Will Have to Make It.

Step 2: You Will Need : 1) a Match 2) a Small Length of Wire. Wind Wire Tightly on Both Ends of Match to Form the Resistor. You Can Paint the Resistor With Clear Nail Polish to Protect From Moisture.

Step 3: Transistor Q2 Amplifies FET Current to Drive LED.

Step 4: Calibrate Potentiometer VR1 for Minimum Brightness of LED. Watch Video for More Details.

Step 5:



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    Our circuit works but our result is inverted. LED on all the time but when a hand comes near the antennae the LED goes off. We used a Preset of same value instead of a POT. Is that OK?


    I made it but it work only one time after that always led glow

    1 reply

    Hi! FETs are very fragile when exposed to static electricity ( high voltage ) . A simple touch can damage it permanently. That is most probably your case.

    what can this be used for? what are some of its applications that won't mess up the fet?

    Nice, but don't crumble any plastic bags or similar near it. The MOSFET is very easy to destroy due to the high gate impedance.

    With a speaker on the output, you can use it to see what materials are unsuitable for sensitive components storage (almost any) - just keep your distance to keep your MOSFET :).

    What kind of wire and what size/length for the resistor?

    1 reply

    Any kind of wire will do ( Not insulated ) . The length of the resistor is the length of the wood match. Make sure it's perfectly dry. Thanks for commenting !