All night test - Complete!

I finally got the thermostat working. I added a delay to the relay loop that makes it wait ~ 3 minutes before shutting off the relay and ~ 3 minutes before turning on the relay.

This keeps the relay/freezer from thrashing (turning on and off rapidly) when the temperature is on the cusp. I ran it all night with the set temp at 50° when I got up this morning the current temp was 48° FTW!

I’m going to lengthen the delay a little bit and add 1° to the upward set temp so it stays off longer on the temperature rise and gives a bigger compressor rest zone between runs.

Pictures and source code to follow.

IT'S DONE! -- Sort of...

The boarduino came Saturday. It took me about 10 minutes to assemble with these instructions: http://www.ladyada.net/make/boarduino/solder.html

I uncharacteristically did not take pictures. The above instructions illustrate the process better than I could.

I soldered all the connections to the peripherals and added connections to the high voltage box. I put it all together, updated the programming and plugged it it. It was a complete success... until... it cooled down to the set temp and began thrashing. The temp flickered back and forth between 51 degrees and 49 degrees about twice a second. The relay was clicking back and forth like a buzzer.

I pulled it out of service and I am working on a way to delay the cycling. My goal is to make it stay on for an extra 10 minutes to allow the temperature to "latch" and stay off on the way up for the same reason.