DIY temp controller

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PintOfBitter

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I just finished building a temperature controller for a mini-fridge I acquired. Total cost was ~$30.00. If anyone is interested, I'll post schematics, PCB layout, part numbers, pics.

I started with the cheapest digital thermostat I could find, and designed an outlet switchbox that interfaces with it. It controls both cool and heat, for use in summer and winter. It can regulate within 1 degree F down to 45 degrees, so not all the way into the lower lager temps. For that, I found the built-in fridge thermostat to be suitable.

Let me know if there's interest.

-PoB
 
I am also interested, I was just going to work on a similar project... I am building a double fermentation box and would like to adjust the cooling/heating accordingly, but this would be a good thing to look at.
 
Alright, I'm home now, and I'll try to take some pictures tonight and clean up my schematics. Wish I'd taken pics during construction. Hindsight is 20/20.

-PoB
 
Alright, here's a writeup about the controller. As it says at the beginning, its not very good, but I'll try to fix it up after some sleep.

Good luck making sense of it. The schematic an PCB images should at least be some help.

DIY Temperature Controller
 
Awesome title for your blog, my roommates all call me an enginerd. I had very similar plans for my temp controller, but was thinking of building the thermostat myself. Maybe I should reconsider. Soon as I can get past all this school work I plan to finish the controller.
 
FWIW, I installed that exact thermostat in my camper and it works great. So far, the thermostat is still running on the original AA battery installed about a year ago.
 
TheFlyingBeer said:
I had very similar plans for my temp controller, but was thinking of building the thermostat myself. Maybe I should reconsider.

I was going to do that as well - i was gonna use a PIC microcontroller and like a TC77 temp sensor... In the end, I'm glad I went the easy route, but I'm sure it would be a rewarding and interesting project to do it yourself. One minor benefit you'd gain is the ability to implement a PID-ish (or maybe fuzzy logic) control to reach a temperature more quickly.

Let me know if you do anything with it - I'd like to check it out.
 
Man, when I was thinking of doing something like this, I was think of it the hard way, straight up analog PID, with a selectable switch for different temps and a TEC for heating/cooling. But this is waaaaay easier. Thanks a bunch for posting this up!
 
what awg wiring is on the power side of that? it looks to be on the smallish side for some applications
 
Well, at least one user has been able to recreate this project successfully. Glad to know it has been a bit of help at least.

I'd usually go overkill on the wire diameter, but in this case it is the best I had. Remember that current (amps) is what determines minimum wire diamter, and voltage determines insulation resistance. The internal wire used here is adequate for the job, considering power draw requirements. It is solid core, which can carry more current, but is less durable (fatigues quickly if bent). Ideally I'd use a heavier gage stranded wire.

Anybody tried this type of project and make any improvements? FWIW, it could probably be assembled on perfboard instead of etching a custom PCB.
 
PintOfBitter said:
Anybody tried this type of project and make any improvements? FWIW, it could probably be assembled on perfboard instead of etching a custom PCB.

I have a custom temp controller; it's microcontroller based, and has some cool features... see https://www.homebrewtalk.com/showthread.php?t=40997

I've upgraded most everything since I wrote that article... maybe I'll find to write up the newest version, some day.. (-:

S
 
Maybe I am wrong, please correct me if I am, but shouldnt the schematic look like this?

EDIT: I revised it to closer reflect what the BLOG describes for the temp controller, and removed unnecessary items left in the schematic. HOWEVER, I HAVE NOT BEEN TOLD IF MY EDITS ARE CORRECT...WITH THAT SAID, USE THIS AS ONLY A REFERENCE TO THE ORIGINAL DESIGN AND BLOG DIRECTIONS.

ControlSch2.gif
 
This is really cool, I wonder if you could use a programmable home thermostat with this same idea to create different 'steps' of temperature for automatic step mashing?
 
OK, so I had started making revisions to this so it could be built on a single sided PCB back in late August early September, but put it on hold while I studied for my PE exam (by the way i passed).

So now I am back on it, and will upload the photos soon, currently etching the PCB.
 
Ok - so here are some of the in process pics. First off I drew the circuit board in AutoCAD since I know I can make it print to the exact scale I want. However, it makes it very difficult to share with others. I tried exporting as a bitmap, but the scale explodes to a much larger size. So as soon as I figure out a good way to share it....I'll upload it.

First off this place gives a great tutorial on how to make PCB's with cheap resources, and is what I used.

Make PCBs at home with magazine paper and your laser printer

Here is my printout on paper from an ad from a magazine (mirrored of couse so when it transfers it comes out the right way). The laser printout was low on toner, and portions of the circuit came out a bit gray.

papermy0.jpg


Here is the transfer, you can cleary see where the toner was low. But no worries, easy way to fix it up.

initialzy5.jpg


I had this from years ago, its PCB transfer paper from radio shack. Its a rub-transfer to make PCBs. I used it as well as a sharpie marker (sharpies are resistant to pcb etcheant acid) to clean up the areas that transferred poorly to the copper.

transfergz4.jpg


Here it is all fixed up.
partialkb1.jpg
 
Here it is etched about 25 minutes in the etchant and toner/sharpie cleaned off.

etchedxz9.jpg
 
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