Fermentation Temperature Controller

---Terrible writeup, but it should be enough to build the controller. Written by a tired brain.---

This is a cheap, accurate temperature controller suitable for maintaining optimal fermentation temperatures of beer, wine, mead, cider, yogurt, sourdough cultures, and other wonderful exploitations of the various microbes present throughout creation.

The controller is usable for both heating and cooling functions, and is based on a cheap digital home thermostat.

Here's what I built, and what you will build if you choose to follow:

Doesn't look exceptionally pretty, but it's pretty versatile. You could mount this on a fridge or leave it cords-akimbo for use in different places. My controller uses a home-etched PCB, which is easy to make, but requires a laser printer and a few extra items, see below.
The thermistor is removed from the thermostat and attached by a long lead for versatility. The lead is flat phone cord to make it easier to close into a fridge door, etc.

::::WARNING::::
I haven't included any safety in the circuit, such as a fuse. Bear in mind that, while my controller works, this info may be flawed. Use your brain and don't take these instructions for granted. I used fairly small gauge wire throughout, as a kind of fuse, but this is not very intelligent.

Shopping List:

• 1x Hunter Just Right Digital Electronic Thermostat, Walmart, $19.99?
  
• 1x Project Box, i.e. Digi-Key P/N 377-1165-ND, $3
  
• 1x Black houshold outlet - rectangular outline, Lowe's, ~$2.50
• 2x 10A Relay, Digi-Key P/N PB766-ND, $1.08 ea.
• 1x 7805 5V voltage regulator, i.e. Digi-Key P/N 296-1974-5-ND, $0.81
• Heat-shrinkable tubing, 1/8"
• Old unused power cord, i.e. from a computer.
  
• Stranded hookup wire
  
• Telephone cord or other 2-conductor cable
• Multi-conductor cable, at least 3 conductors
• Old AC/DC wall adapter, between 5 and 15 volts, the smaller the size the better.

For the PCB: (see http://www.fullnet.com/~tomg/gooteepc.htm for info on making PCBs)

• Inkjet photo paper
• Laser printer
• 2-sided copper clad board, 2 ounce cladding. (uses about 3x3 inches)
• Copper etchant such as ferric chloride

The Steps:

1. Create the PCB, if you choose to use one. The copper images and layout are below. You'll have to resize them for printing - the board outline is 3" by 2". The top copper is already mirrored. Once the PCBs are etched, carefully drill all the holes (some of them are unused, see layout diagram) Note the eight drills that are layer transfers - you'll need to solder a piece of wire through each of these to form vias.
2. Cut a hole in the project box, all the way at one end, that the outlet fits into. You'll have to bend up one of the mounting ears of the outlet to get it as snug up against the end as possible. Drill screw holes to mount the outlet. Break the little tab that connects the screw-down terminals of the hot side of the outlet to isolate the two plugs. Leave the return side intact. Screw down a length of wire to each terminal - these will be connected to the board. Drill holes to accommodate the power cable and multi-conductor cable.
3. 
   
4. Remove the back cover from the thermostat. Remove every screw that has an arrow next to it to remove the "motherboard" of the thermostat. Carefully desolder the thermistor (fragile looking thing with a white plastic hoop cage protecting it) without heating it too much or physically damaging it. Solder the phone cord into where it used to live.I zip-tied the phone cord to the cage. Now resolder the thermistor to the other end of the phone cord, insulating the leads with electrical tape, and then wrap it all up in heatshrink, leaving the tip of the thermistor exposed to the air:This is your remote temperature probe. You may want to check to make sure that the unit reads the same ambient room temperature before the de- and re-soldering and afterwards. I found it was unaffected.
   
5. Assemble the circuit, either in the PCB or on perforated prototyping board or however else you want to do it. See schematic:Be sure to also connect the ground of the power cord to the ground terminal of the outlet. The AC/DC adapter can be located externally, or disassembled and packed in the project box. This was an ugly mess in my case, but is perfectly functional. If you choose to package the adapter within the box, you'll need to find a spot on the PCB to connect to hot and return to supply the adapter. The layout image above will help with locating the thermostat connections. The only necessary thermostat connections go as follows (referencing the layout diagram): Y on the thermostat connects to the CoolRelay connection in the row of "Thermostat" connections. The next connection over from it should be connected to W, skip the next (though it must have a via soldered in to connect the two layers), and connect one of the remaining two connections (they're common to each other) to Rh. Leave the jumper wire that is in the thermostat where it's at, connecting Rh and Rc. Cut out a few of the vent ribs to make passage for the cable, and zip-tie it in place. Now put everything together - tuck it all tidily into the project box, and be sure to isolate with plenty of electrical tape where needed, especially if you gutted the AC/DC adapter to fit it in the box. Plug it in carefully and test it out. Keep in mind that the thermostat is made to protect air conditioning systems from starting less than a few minutes after last shutting off, so the switching may appear to not be working, depending on how you test it.

That's it. Hopefully yours will work right away. There is plenty of room for improvement in this design. You may have noticed the extra connections available in the Thermostat portion of the PCB. These were to supply power to the thermostat, and eliminate the need for batteries - I decided a battery backup was probably a good thing to have, and so I didn't use them.

Please be careful, and have fun.