Arduino Binary Alarm Clock

Step 8 The snooze touch sensor

The principle behind the touch sensor is quite simple. It uses two pins; a send pin and a recieve pin. A resistor connects the two pins, and something conductive, e.g a piece of aluminum foil, is connected to the recieve pin. The foil will work as a capacitor

When the send pin toggles state, the recieve pin will also, but with a slight delay, depending on the size of the resistor and the capacitor. If something conductive, e.g your hand, comes close to the foil the capacitence will change. This will cause the delay to also change,  so by measuring the delay you will know if something is close to the sensor.

There's a good library that does all this measuring for you, called CapSense, written by Paul Badger. Info about the library and a better explanation of how the sensors work can be found here: CapSense library

Building the touch sensor:

1. Attach the aluminium tape or foil on the inside of the box lid.
2. Strip of the insulation from the end of a wire and tape it to the aluminum.
3. solder a 1 MΩ resistor to the other side of the wire. (The value of the resistor isn't critical, but has to be fairly high, just try with what you have handy and see if it works )
4. Cut out a piece of paper that covers the inside of the lid.
5. Glue the paper over the aluminum foil.