Sunday, November 19, 2017

New sensor board in the making

I'm trying to be far more careful now about how I build up and qualify my boards. I got 6 boards made from Osh Park and fully stuffed one of them yesterday. Today, I'm doing a step by step qualification to make sure everything works well.

I attached a Fio V3 to the board with a temporary header and rubber bands (someone should make Cleco fasteners for 0.1 inch headers!!) and used a Sparkfun TMP102 breakout board I had lying around as a generic I2C device to test the pressure sensor slots (so I don't risk my actual, expensive pressure sensors).

First, I learned that unless I de-populated the pullup resistors and decoupling cap on the TMP102 breakout, the bus did not work properly. I suspect it was the pullups that were overwhelming the bus, given that my board already has pullups.

With that fixed, I was able to verify that each of the pressure sensor slots were interrogated correctly by my bus scanner and that the TMP102 showed up where I expected it to.

Here is a picture of my test setup, followed by a picture of the signals as digital and analog traces on the scope. You can see how each of my 4 I2C buses is lit up in sequence by my bus scanner program.




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