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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    8 Discussions

    0
    f8eho
    f8eho

    2 years ago

    Nice, and fun resistor :) but one can find 1 gohm resistor at Farnel, mouser, etc, but the match is cheaper :)

    0
    bentlijsa
    bentlijsa

    Question 2 years ago

    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?

    0
    ChitranshN2
    ChitranshN2

    2 years ago

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

    0
    simpletronic
    simpletronic

    Reply 2 years ago

    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.

    0
    deathofme
    deathofme

    5 years ago

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

    0
    Omnivent
    Omnivent

    5 years ago on Introduction

    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 :).

    0
    acheide
    acheide

    5 years ago on Introduction

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

    0
    simpletronic
    simpletronic

    Reply 5 years ago on Introduction

    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 !