Halloween is approaching and crazy minds are generating new ideas of making fun. NerdKits decided to trick everyone with spooky candle bowl which lights up when someone decides to reach in. They use two aluminum foil sheets that act as capacitor. One lied on the ground or table and another inside pumpkin perpendicularly. Capacitor is connected to microcontroller pin which actually charges capacitor and then measures capacitor discharge time through resistor. If someones hand is near foil capacitor it takes longer time to discharge (we all know that we are mostly water) – this is what AVR comparator detects.

After someone is detected there comes time to act. In this case LED eyes are controlled by PWM signal. But do not limit yourself – it can be scary sound or some motor activated action. You can find the source code here so you could expand your DIY possibilities.