I'm building a mixed analog and digital circuit on a breadboard, using an AVR and a DAC. I have separate analog and digital ground planes connected in only one place, with plenty of 0.1uF and 0.01uF bypass capacitors.
However, it looks like the AVR is causing spikes on the supply and ground lines when certain pins change. The spikes are leaking into the analog ground and are quite noticeable in my output.
How can I either 1) prevent the digital part of my circuit from causing spikes on the supply and ground lines, or 2) completely isolate the spikes from the analog portion of my circuit? I put a 0.1uF bypass capacitor between the AVR's Vcc and GND pins, but that didn't seem to do much.