Post by thread:[EE]: Need an AC line interface circuit for ADC

I need a circuit that can attenuate (is that the word?) a 110vac to 140vac (rms.) voltage down to a readable voltage for the ADC on a PIC (5volts and under). It has to be fairly accurate (within 1%), or be setup to be self calibrating (preferable). For example, if the AC RMS voltage is 135vac, then Vpeak would be 190.947 volts, and it would have to be translated down to 5VDC. Also, I'm not sure where I should set the top end of it.... I'm assuming most places in the US don't go much over 140VAC (RMS). I'm wanting to use the most steps (8 bit ADC) for the best accuracy, but don't want to have the device not work if the user's nominal voltage is normally above my top end settings. Any suggestions, or comments, on where it should be set at? Sorry, I can't be using a transformer for this, and I'd rather not have to resort to trim pots in the design either if possible (manual setup, and they drift over time). Any help on this would be greatly appreciated... Hopefully this message will FINALLY get sent to somewhere other than the OT list. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements