Read the Instructions... Thoroughly!

I reported recently on completing the assembly of the power board. The designers of the PANOPTES system and the beta-test builders (I'm in that latter group) had discussed the fact that the instructions were structured in a way that made for some awkward steps: some tall parts are added before adjacent short parts, etc. I resolved to come up with an alternate assembly process that would be focused on efficient assembly. I went through the existing instructions, the PCB layout and parts list, figuring out which parts needed to be inserted from the bottom of the board, which from the top, and which could go on either side. I also sorted them by height and by side of the board. Altogether this seemed to result in a pretty easy assembly.

I celebrated Independence Day by continuing work on the build, focusing on finishing up the electronics. I finished creating cables for the sensors, and was finally ready for testing the boards. First up, the Power Board. I plugged a fan into the fan output, and provided 12V power to the board. The fan came on. Yeah! The LEDs showing the fan was on did not come on. Oops. I started probing the board with a multimeter, and discovered that the LED came on if I grounded some spot near it, which shouldn't have happened. So I decided I'd better re-read the instructions.

By the time I got to assembling this third and final PANOPTES board, I was used to the preamble at the start of each instructions document: title, image of the schematic or layout, list of tools needed, etc. I had skipped right past those and proceeded with my study of the detailed instructions. In fact, I skipped right past the warning that said to read another document FIRST if you were working with V0 of the board... which I was.

That document was a repair document. It turns out that the PCB layout was has an error. Well, 5 errors. The footprint for the Solid State Relay had two of the pins reversed, with the effect that each of the 5 SSRs was not being used as a switch, and 12V was flowing to the outputs at all times. Not good. But there was a simple fix: raise the SSRs up, with a pair of wires underneath providing a cross-over. Except they were already soldered in place.

I decided to try the other option listed in the repair doc: cutting traces on either side of the two swapped pins on each of the 5 SSRs, for 10 cuts, and then soldering wires to pins to get 12V in and out of each SSR via the opposite pin from the PCB layout. This was a bit tedious. So much effort, my effort, could have been saved by more careful reading, by me. Sigh.

Fortunately the repairs worked. The lines are now switched based on inputs from the ribbon cable connector... I also screwed up the ribbon cable: after carefully studying the connectors, I still put one on the cable the wrong way around. Fortunately I ordered 3 connectors, just in case I screwed something up, and fortunately I didn't make the cable super short, though I now wish I'd allowed a bit more room. Now I need to test the other boards, and later I need to calibrate the current sensors on the power board (those red daughter boards in the picture above).


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