Studying Capacitor

The RC circuit under study is connected between the Digital output socket D3 and Ground. The voltage across the capacitor is monitored by the ADC channel 0. The voltage on D3 can be set to 0V or 5V under software control. Taking D3 to 5V will make the capacitor charge to 5V through the resistor R and then taking D3 to 0V will cause it to discharge. All we need to do is digitize the voltage across C just after changing the output of D3.