(Unlike earlier project logs, this is happening in real-time, and not a post about a previously occurring event)

In earlier discussions with my wife, when the project was in a "moving along quickly" phase, we had the idea that maybe the board would need to be smart enough to auto tune the IR sensitivity. The current scheme has a single 10K pot on each of the 9 boards, run in parallel to all 25 comparators on that board. Each 10K pot is a single turn, and is hooked to the 5V rail, so they can be pretty touchy...

Now that there is a Teensy 3.2 on board, I have an actual analog output to work with. I was considering just tying the DAC output to all 225 comparators (probably through a voltage follower to act as a buffer), but I really like the ability to tweak each board individually. So instead, I think i'll hook the DAC output to the top of all 9 10K pots. This would be the equivalent of a 1K load on the DAC, so it would draw ~3mA at 3.3V. A brief search suggests that the DAC can really only put out 1mA, so the voltage follower is still on the table as an option. This should give me global software control of the voltage, with local tweaks for any irregularities.

A blue sky version of this might actually sweep the voltage and use that to build a 3D distance map, but that seems excessive...

Since the output of the 10K pots is usually in the 0.5 to 0.7 V range, I'll target 1.5V as a starting value with all the pots around halfway to see if this improves the sensing, especially as I go to add the diffuser and such, which will mess with the IR signal.

Step 1 - cut the trace from the adjustment pot to the 5V rail:

Step 2 - set the DAC output to a constant voltage to test.

Step 3 - construct a voltage follower on a spare LM339. The blue wire comes from the DAC.

Step 4 - daisy chain the output voltage across the first three adjustment pots and test.

This actually all seemed to work. I was able to adjust the pots up to .62V which gives a reasonable IR sensing range, and the actual adjustment was far less touchy. In the next log, I'll continue the daisy chain to the rest of the pots, and then start thinking about a calibration routine (and how to trigger it!).