Hi All, Ok, more on the dreaded color reader problems... ;-)
Now that I have the scope, been troubleshooting this thing a bit. One thing I am seeing is that there is a lot of noise on my power net. While the chip's specs say it should have a ripple of around 40mVs, I am also seeing a noise signal around every 100ns of 200mV p-p. I haven't been able to figure out what is causing it. It is there even when the mcu is in break or asleep, so it doesn't seem to be from therre. The LED power supply is shut down, so it shouldn't be from there. The only things power up are the opamps and the digital pot.
I have a 10uF next to the PSU chip, another 10uF on the same rail by the other PSU chip. I have a full copper pour for both ground and Vcc, and 1uF bypasses next to each chip (and two by the MCU.)
So, any ideas? That noise pulse is only around 100us wide, but fairly regular. If it was the opamp oscilating, I would have expected more of either a square or sine wave, instead of just regular pulses...
Thanks, Charlie