The finished controller

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.

Making the temperature probe

I'm making the temperature probe to go in the main body of the freezer out of

• 4 feet of cat 5 cable
• 1 LM-34 temp sensor
• 1 3 inch length of 3/8 inch copper tube
• Electrical tape
• JB Weld

I started by unjacketing the cat 5 and untwisting one pair (orange). I then retwisted the solid orange onto the blue - blue/white pair.

Next I soldered the wires to the legs of the LM-34 and TESTED it. I've built stuff like this in the past and not tested it before I commited to making it a permanent installation. Bad idea.

Then I wrapped the legs in electrical tape and dry fitted it in the tube

Next I mixed up some JB weld and slathered it over the sensor and pulled it back into the tube. I then scooped more JB weld into the end of the tube, taped both ends and hung it up to set overnight. I'll fill the tube completely in the morning with thinned JB weld and then let it rest 24 hours before I'll deem it "ready."