Electronics Progress

25 Mar 2020electronics

I’ve been making some progress with Contextual Electronics, and have been learning a lot, although some of the learning has been a little painful and frustrating.

The bad news first: I screwed up the sizes of some component footprints, had boards made, and the parts (of course) didn’t fit on the footprints! That affected both the CE header sensor board (which has a 74HC595 shift register on it) and my example Morse blinky board (which has a pile of 74xx logic chips on it, all of which were affected).

I tried soldering the parts on with paste and hot air, but the mismatch between parts and footprints is too large. The Morse blinky is a dead loss, but I got three boards made by OSH Park and ordered extra components, so I’m going to try assembling another one following a suggestion from Chris Gammell (who has apparently encountered this problem in the past as well). He says that you can bend the pins of SOIC packages under, which gives a reasonable chance of soldering them to the smaller footprint. I’ll give that a try!

The CE header and sensor board, after a bit of component reordering (I had another footprint mess-up and I got some weird-looking pin header sockets that don’t fit normal 0.1” pin headers) mostly works. The shift register is defunct (I’ll try the same pins-under trick on that too), but the LDR light sensor and the temperature sensor work fine. The connection between the Teensy and the sensor board via the extra breakout board works well, and soldering all the headers on was nice and easy (much easier than soldering SMD components!).

The sensor board + breakout board + Teensy assembly looks like this (you can’t really see how bad the soldering of the shift register is, but it’s pretty bad):

CE sensor board

Even though the shift register was broken, I could do something with the light and temperature sensors, so I wrote a little bit of Arduino code and some Go code to run on my laptop to collect light and temperature data. That worked pretty well:

Light and temperature data

The light data is reasonably interesting: I left one of the blinds open so that you can see the sun coming up in the morning. And yes, unfortunately I did go to bed at exactly midnight, leading to what looks like some sort of anomaly as I switched the lights off just then!

I’ll see if I can fix the shift register to finish off the other parts of this project.