Improved ADC Pin Techniques
I have been on a detour from USB stuff to work out some software techniques for improving instrumentation ADC performance on single I/O pins.
It turns out that SINC2 manual mode in the smart pin can be exploited for making accumulated measurements which integrate many short, interleaved GND, VIO, and pin measurements. This takes very little software and we can get to 16 bits, at least, with long sample times.
Tomorrow, I will post some example code here. This has been very exciting to work on. Every day, I have been able to find ways to realize big improvements, after I thought I had hit hard limits the day before.
Here are some pictures of captured waveforms that are only 1 mV peak-to-peak, across the entire -200mV to +3.5V range, and are 1 Hz, to allow for long sampling times. Samples are reported in microvolts!
You could use this directly for EKG, for example. No special low-voltage analog circuitry needed.
These techniques can also yield 10-bit instrumentation samples at 250 KHz. By instrumentation, I mean absolute voltage registration, not AC measurements.