> Is electronic that limited ?? C'mon, there should be a trick ! I've been thinking about it, and came to the conclusion that the most important "trick" a auto-ranging DMM uses is - impedance. A DMM has an input impedance of at least 1 megohm, so if you connect it to a kilovolt, there's only 1mA running. That is easily catched by a diode, and the electronics behind it is protected. Then you see that you're out of range, and switch to a different voltage divider, a different fixed-gain amplifier or adjust the gain of a variable-gain amplifier. I presume, good DMMs use reed relays to really mechanically switch voltage dividers.
You can't use this technique directly on PICs, as their ADC require quite a low impedance, no more than 10kohms. So you would need a FET-OP-Amp to translate the megohm input to a low impedance output suitable for the PIC input. So much for measuring theory ;-) For the primary case here, measuring 5 or 12 or 24 volts, this would be a bit of an overkill. The solutions already given in this thread should all be worth a try, they're all quite simple but sufficient. Greets, Kiste -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
