Tiny84 ADC in differential/bipolar mode
2010-10-08 by Mark Nowell
Is anyone here familiar with the Tiny ADC in this mode? I'm using ADC0/1 in differential mode with ADC0 tied to an external Vref of ~2V and ADC1 variable either side of this, 5V rail. If I remove the bipolar (BIN) bit I get what I'd expect which is roughly 5mV/bit when +ve, and 0 otherwise. If I set BIN I do get bipolar readings but I appear to get 18mV/bit resolution and a reading of 284H with both chans equal. This looks suspiciously like I'm losing 2 bits of resolution where the datasheet says I'll get 9-bit plus sign. I've no idea where the absolute values are coming from. The intention is to use this approach to sample a current transformer with 0-5V output and it's own centre reference. I'm targeting Tiny45 for production but using Tiny84 for debug. This differential/bipolar setup seems the appropriate one but I'm starting to think I might have to try something else. Thanks, Mark