Hello Nigel
Thanks for your comments and advice. I agree that PIC microcontrollers can make good stand alone (not relying on a PC) data loggers. This is something I like to do later.
Before I got the time to learn PIC, I would still prefer to use readily available PCs, if I can find a way. One suggestion is to employ a simple VCO, so that the voltage level to be measured is converted into a corresponding frequency of an oscillator. The signal is fed to the line-in of the sound card. What we need to do now is to write a program, say in Visual Basic, to monitor the frequency and convert it back to voltage data.
How can I write such a program? I have the basic programming knowledge if Visual Basic, but I have no idea how to get the frequency values out from the sound card!
I need help --- any one please!
Thanks !
Olihou