The capacitor is charged with a constant current supplied by the transistor. The capacitor voltage will rise linearly. To discharge the capacitor, the AIN0-pin is set to output with a "0" applied. A reference voltage at VCC/2 is supplied by the resistor network R ref1 a nd R ref2. When the PB1 and PB2-pins are configured as inputs, the reference is turned off, and the voltage level at the AIN1-pin will be the input voltage Vin. By setting the pins as outputs and applying a "0" and a "1", the level at the AIN1pin will be VCC/2 (if the resistors are of equal size). The input resistor Rin have to be at least 100 times higher than the reference resistors Rref1 and Rref2 to avoid measurement errors.