This project was inspired by the convergence of two random events. The first was a Facebook posting about a rather intriguing Kickstarter for a product called the HopTop, which allows you to turn any Mason Jar into a brewing/fermentation chamber. The second was a neighbor who put a broken Cuisinart wine fridge on the curb. My brain quickly saw these as two great projects that work great together, and synergy quickly fermented in my psyche. (I have actually received my HopTop Brew Kit, making this the only successful fundraiser in which I have participated.)

The HopTop is a fantastic tool for small-batch fermentation, and now I can fiddle with my own stouts and meads without having to tie up the resources of a bunch of five gallon carboys. But, since I live in a house without central air conditioning, I'm rather limited in what time of year I can work on such projects. Enter the Cuisinart wine fridge. These little darlings are built with peltier junction heat pumps, which make them wonderfully quiet compared to traditional refrigeration systems. The real magick of peltier junctions is that they can pump heat in either direction, just by flipping the current flow. Since the unit I curb-rescued had a broken controller, I was going to have to home-brew a new controller anyways, so I might as well make it into a general-purpose programmable temperature controlled system that would be perfect for customized fermentation temperatures.

And so was born the Brew-a-Tron 3000: a precision temperature controlled chamber that is perfect for brewing, fermentation, sourdough cultures, mushroom colonies, or any other project where you need to maintain a consistent temperature.

Features:

Precision temperature control
RGB back-light indicates mode
Buttons control temperature and +/- allowance
Settings stored to EEPROM for recovery from power loss
Data logging to the SD card

Step 1: Tear It All Down!

To build it up, we first have to tear it apart. Repeat after me: "I void warranties!"

While I won't be using the built in LED display or control buttons, I'm leaving them in place rather than mess op the inside of the insulated chamber.

The controller and power supply are integrated in this unit, and I don't plan on spending any time figuring out what's wrong with it. My home-brew controller will be better anyways, as it will heat or cool the chamber as appropriate to maintain the specified temperature. I'm removing the controller board and chucking it in my "if I'm ever really really really bored" box. (AKA by e-waste bin)

I've pulled out the peltier heat pump modules for two reasons. First is take a couple pics so you see what we're working with. Second is to clean the fans, since I don't know what kind of environment this system previously inhabited.

Step 2: Parts, Parts, Parts...

So, we need to add a few things to replace the controller and power supply we removed.

Arduino Uno
Adafruit Datalogging Shield wth RTC and stacking headers
Adafruit RGB LCD Shield with buttons
4 Relay Module
12v 20A power supply
12v -> 5v DC/DC converter
10k resistor
4GB SD card

Step 3: Wiring It Up

Power relay:

We are going to use three out of the four relays on the board. R1 & R2 are for the Peltier junctions, and R3 is for the external fan. First step is to wire all three up identically. +12v to the left arm on each relay, and GND to the right arm. In this configuration, the default state of each relay will be to have the switch connected to GND.

Connect the black leads from the peltier junctions together, and screw them into the center connector on R4.

Connect the red leads from the peltier junctions together, and screw them into the center connector on R3.

Connect the GND leads on the external fans together, and connect them to GND on the power supply.

Connect the +12v leads on the external fans together, and screw them into the center connector on R2.

Connect Vcc on the relay board to 5v on the Arduino. Connect GND on the relay board to GND on the Arduino.

Connect IN1,IN2,IN3,IN4 on the relay board to D4,D5,D6,D7 on the Arduino.

Temperature Sensor:

The wine fridge already has an internal temperature sensor, in the form of a 10k Thermistor. Using the awesome guide at Adafruit, we are going to wire in the Thermistor to A0 using a 10k resistor and using 3.3v via AREF for cleaner readings. I'm horrid at pretty pictures, so please consult Adafruit: https://learn.adafruit.com/thermistor/using-a-thermistor

12v -> 5v DC/DC Converter:

On my first pass, I tried powering the Arduino off the 12v power supply, and the relays off the Arduino's built-in 5v regulator. That was a near disaster. The regulator isn't up to the job of running two relays (the max this system has on at any time) and the Arduino, and it was extremely hot to the touch. To reduce the chance of frying it all, used a 12v -> 5v converter, and wired it directly into GND and 5v via an easily disconnected 5mm barrel connector assembly.

Internal Fans:

The external fans are connected to the relays, and are only powered when the peltiers are powered. I wired the internal fans directly to the 12v power supply, so that they are always running. The idea is to keep the air inside the chamber circulating, which should help keep the temperature even throughout the chamber.

Step 4: Load the Code!

The code is currently published on my github account: Ferment-a-Tron 3000

Highlights:

The sketch uses the four 'direction buttons' to control the temperature and the allowable drift.
Pressing the Select button will write the current settings to EEPROM, which are loaded at reset.
The RBG backlight is used to indicate the mode the system is in:
- WHITE - The system is at the correct temp and the peltiers are idle
- BLUE - The temperature needs to be reduced, and the peltiers are cooling the chamber.
- RED - The temperature needs to be raised, and the peltiers are warming the chamber.
Data is logged to the SD card every ten seconds to a CSV file

Once you've got the system running, I recommend commenting out the line '#define DEBUG 1' as that code is only useful when debugging the system.

Send me comments, fork it, etc. As I just 'finished' this project, I expect to be tweaking the code for the next couple of weeks. Especially as I start to make use of my HopTops. :)

Step 5: Errata

I think I need to use a more bigger power supply. I'm not getting as large of a temperature differential between the chamber and the outside air as I would have expected. Not critical, as it holds brewing/fermentation temperature just fine. I just can't help thinking that if I drop in a PC power supply I can get rid of teh DC/DC converter as well.
I might add a second temperature sensor outside the chamber, so that I can log ambient air temp as part of the data collected.