Mini 3-channel ADC

This month we'll make use of the ATTiny13 again. This versatile microcontroller is used here in a practical, compact voltmeter with an RS232 link for use ‘on the road’.
We show you how to build a small device that wouldn't be out of place in the laptop case of an electronics fanatic. It is a three-channel A/D converter/voltmeter, connected via the serial port. Whether you want to measure transistor characteristics, battery discharge characteristics or just measure the voltage at a few points, this circuit can help you out as long as the voltages are between 0 and 5 V.