Easy, Cheap & Reliable Touch Sensor With Only 3 Parts

Controllig all kinds of electronic devices with the touch of your finger can be quite useful.

In this instructable I will show you, how to build an easy but powerful touch sensor which works flawlessly. All you need is a standard transistor and two resistors for the main part and an Arduino or a voltage comparator to do something with the signal.

I'm not really sure how it works, but it's the best and easiest touch sensor I've built so far.

Usually such a touch sensor is called a 'resistive touch sensor'. It requires two electrodes and when you touch it, a small current flows through your finger which is amplified by a transistor and then measured.

My detector, however, requires only one electrode. My theory, so far, is that when you touch the electrode a small current flows through your body to ground which is then amplified and so on.

The second type of sensor is called 'capacitive touch sensor'. It detects your finger without touching the electrode by measuring its influence on the capacitance of the electrode. This method of detection is also used in smartphones but it's, as I've experienced myself, quite difficult to get working because it has to be fine tuned to the size of your electrode.

My new sensor combines the advantages of both because you only need one electrode but still have simplicity and therefore reliability and independece of the electrodes size.

Supplies

1x Transistor: BC557B

1x Resistor: 5k

1x Resistor: 4M

Optional: Breadboard, Arduino, Voltage Comparator, Jumper cables, LEDs ...

Step 1: Gathering the Components

All of the components can be bought online very easily or sourced from a local electronics market.

Step 2: Build It!

The three components need to be placed on a breadboard (or soldered together) as shown in the picture.

Then an external device (in my case an Arduino) is hooked up to it to detect something.

Step 3: Have Fun With It

Now that you have built the main part, you can use it as follows: If you don't touch the electrode, the arduino will read 5V (1023) at the Output. But if you do touch it, the voltage will drop below this value.This way your finger can be detected.