Touch sensor
This is a simple circuit which can detect when you touch a sensor connected to one of the sensor inputs. It can be used to add a touch switch to your computer for example. It uses an AVR micro controller, the AT90S2313. This is overkill. You can add a lot more sensors than the two sensors.The basic idea is really simple. Make one pin output and another input. Connect a resistor between these pins.The resistor together with the human capacitance forms an RC network. The AVR set the output to low and then make a transition from 0V to +5V. 5 ยตs after this switch, the logic level at the input pin is sampled. If someone is touching the probe connected to the input pin, the capacitor (=human) will not be fully charged, and the input will be a digital 0 and vice versa.
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