…I had originally targeted using an old 35mm film canister as the “chassis”. I only had one film canister and our cat took off with it! I ended up housing the unit in a vintage pill bottle.
Adafruit has the Trinket now, I would have used one of those for this project if they were available at the time. I had already found a handful of these clone “New Version Pro Mini Module Atmega328 5v 16M” and started my build around it. The goal for the build was to keep the project as compact as possible while leaving room for future expansion as I learned. Now that I know more I can think of many alternatives, for example to create my my own board from scratch with a socket for the Arduino and put it all in a mint tin, or simply mounting the unit I have on a board and building around it. But using a shield did save me some grief — at one point, I zapped one of my boards with direct 12v power. Had I soldered it in place I would have had to rework a lot of pins.
This was a little expensive – the power supply and SSRs are overkill – but it was fun to make it so small. I forgot to mention that using the SSRs meant I did not have to put a diode (snubber) to protect the circuit from the relay coil.
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