Saturday, September 16, 2017

The dreaded electronic crickets

My greatest dread and fear is of electronic crickets. I put a circuit together, as carefully as I can, plug it in, and ... crickets. Nothing. Nada. Not a peep. Well so it happened today.

I soldered one I2C mux chip and some resistors and capacitors into the board I had made. Soldering the SMTs was not easy, and it's clear that I need at least a good magnifier of some sort and a good pair of very precise tweezers. I then pulled off some signals from the board to see if the I2C mux would successfully mux in a BMP280 pressure sensor breakout board, thus verifying that at least some of the things I put on there were doing their job.

The result was, no detectable I2C presence.

Ok so I imagine the problem is that I failed to tie the address pins (A1, A2, A3) of the I2C mux either high or low, so who knows what address the thing happens to be sitting on right now. This is a pretty elementary boo-boo, and I note (ex post facto as it turns out) that the Adafruit breakout board does indeed tie these pins low, and provides a way for you to override that.

Another boo-boo I made is that, in the mounting for the BMP280 board, I failed to pay attention to the hole diameter -- I ended up making holes suitable for an IC, but not for a (much thicker) 0.1" header.

So I think I have decided to skip bare board manufacturing for now. I'm sure I can learn the necessary skills but that is for another day.

That said, I can still get boards made to mount the breakout boards into -- that will save me from a lot of flimsy and error-prone hand wiring, and will save some space inside my probe.




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