I built this serial voltmeter a few years ago and now use it to measure the voltage of my solar system every five minutes. See the current voltage and daily graph.
Design and Software
The following shows how to use an analog to digital converter to measure voltages and transmit the data to a computer's serial port.Basic design revised from beyondlogic.com
Serial port reference information from beyondlogic.com
Datasheets for the ICs
Last modified: July 17, 2009