Thanks for the comment on the leakage current, I had not thought of that. I think that you are correct in that I should just run at full speed on the internal oscillator and use the WDT to wake up when I need to do a conversion. -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Mike Sent: Monday, June 30, 2014 7:06 AM To: piclist@mit.edu Subject: Re: [PIC] Using ADC in PIC12F683 with Low-Speed Internal Oscillato= r (LFINTOSC) PICLIST platinum.ca> writes: > My sampling circuit will be a relatively high impedance voltage=20 > divider off of the 12V battery, but I'm assuming that if I give the=20 > ADC lots of time to settle (i.e. a large fraction of a second), I=20 > should be OK with a 200K+ input impedance. You really need to consider the input pin leakage currents before jumping t= o any conclusions. No matter how slow you perform a conversion, or how much capacitance you use for decoupling, input leakage will give you the same error. Datasheet says +-0.1uA typical, +-1.0uA maximum. With your 200k input impedance that would give a typical offset error of 0.02v and a maximum of 0.2v . And since this is a leakage current it will very likely vary with temperature. Also check the current that the A/D requires during conversion from the Vre= f source, you may well be using more power by running the A/D clock so slowly= .. Your requirements of simply taking a sample about 1 per second could be ver= y easily implemented by using the watchdog timer to wake the part from sleep. You could then simply use the internal RC oscillator running at whatever speed is appropriate (i.e. 125kHz up to 8MHz) to perform any processing before sleeping again. The watchdog takes around ~1uA, and the rest of the device will be in the low picoamps range if correctly configured before sleeping. Mike -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .