This is a simple temperature controller, aimed at overriding the thermostat in a refrigerator or freezer to allow warmer temperatures for the fermentation of beer (though it could be used for other purposes). It works with 1-Wire devices: a DS18B20 temperature sensor and a DS2406 addressable switch. The latter device controls a solid-state relay, which in turn controls power to the refrigerator. A web interface is included for remote monitoring, or for use with a local display.

I'm writing this to work with a Raspberry Pi, equipped with an Adafruit PiTFT touchscreen and a 1-Wire/I2C adapter board of my own design. The adapter board design files are at Upverter:

https://upverter.com/salfter/b0ef63c2cd7a37c7/rpi_i2c_1w/

Check the comments for links to order bare boards and parts to assemble your own. It uses the w1_gpio bit-bang driver. Other supported 1-Wire interfaces should also work, as this code works with the /sys/bus/w1 file hierarchy.

Interface

You could run this headless, using a web browser on the device of your choice to control your fridge. However, the interface is designed to fit within the constraints of the PiTFT touchscreen. I have my Raspberry Pi set to auto-login the "pi" user; scripts in /home/pi fire up X, Ratpoison, and Chromium (in kiosk mode). The setup looks something like this (updated 6 February 2020):

packages that need to be installed (assuming we start with Raspbian Lite)

sudo apt-get install ratpoison unclutter chromium nmap xinit

/home/pi/.bash_profile

if [ -z "$DISPLAY" ] && [ $(tty) == /dev/tty1 ]; then
  startx
fi

/home/pi/.xinitrc

exec ratpoison

/home/pi/.ratpoisonrc

banish
exec xset s off
exec xset -dpms
exec unclutter -idle 0
exec /home/pi/start-pifridge.sh

/home/pi/start-pifridge.sh (make sure you chmod +x)

#!/bin/bash
if [ "`nmap -oG - -p 80 localhost | grep open`" == "" ]
then
  sudo nohup /root/pifridge/pifridge.py 2>&1 >/dev/null &
fi
while [ "`nmap -oG - -p 80 localhost | grep open`" == "" ]
do
  sleep 1
done
exec /usr/bin/chromium-browser --incognito --kiosk http://localhost/

unclutter keeps the mouse pointer hidden most of the time...it only comes up when you touch the screen, and then goes away.

nmap is used to verify that pifridge is running before Chromium starts.

(Note: Current releases of Raspbian (as of November 2017) require a Raspberry Pi 2 or later. On a Raspberry Pi or Raspberry Pi Zero, I would recommend substituting Uzbl for Chromium.)

Dependencies

Current releases of Linux for some time have included support for the DS2406. As of February 2015, the kernel included with Raspbian includes the driver as a module.

If you're still running an older kernel (<3.18) for which this support is missing, you might be interested in this patch:

https://alfter.us/wp/wp-content/uploads/2017/11/w1_ds2406.patch

Apply the patch to your kernel source tree, make sure CONFIG_W1_SLAVE_DS2406 is enabled in your config, rebuild, and install.

The web interface uses Flask, simplejson, and matplotlib, so those need to be installed:

sudo apt-get install python-pip python-simplejson python-matplotlib
sudo pip install flask

Writing to the DS2406 (to switch it on and off) needs root access. For that matter, so does Flask if you want it to run on port 80. Therefore, pifridge will need to run as root.