To prepare the screech owl nest box for the possibility of nesting by my local screech owls, as of this evening, I've now evicted various numbers of squirrels from the box three times, have opened-up and cleaned the camera compartments, and have repaired a broken wire from the entryway sensor. So, the box is being kept available to, and ready for, the owls, should a pair choose to claim it this year.
Unfortunately, I still haven't setup the A-to-D converter board I bought to replace the one that burned-out a few years ago, so I have no data on whether, or not, the box is being visited. Hopefully, I'll work-up the energy to do that soon. And this time, I really must use an optoisolator in the circuit.
Otherwise, the only remaining problem with the setup is a semi-persistent humming noise on the audio circuit. It has bedeviled me ever since I put a microphone in the box. I assume that it's a grounding issue, but I've grounded everything I can think of to the common household ground and the problem still occurs. The intermittency of the problem makes trial-and-error resolution especially difficult, although I've pretty much run out of ideas, anyway. Needless to say, I'm open to suggestions from anyone with relevant experience.