This program will control an electric heating element in a vessel to set temperatures and regulate boil. All status included temperature is sent back wirelessly approx. every second. The duty cycle and temperature is plotted in real time. A Type C PID algorithm has been successfully implemented to automatically control the heating element when the desired temperature is set.

<img src="https://github.com/DougEdey/RasPiBrew/raw/master/img/PID_Tuning.png" alt="" width="954 height="476.5" />

The temp plot shows temperature in degrees F over time in seconds.
The heat plot shows duty cycle percentage over time in seconds.

A $35 credit card sized raspberry pi computer is an inexpensive and very expandable solution to controlling a home brewery. Here it is used for temperature control of one vessel. Used in combination with a jeelabs i2c output plug to control relays, 1-wire temperature sensors and a cheap usb wifi dongle a wirelessly controlled temperature controller can be developed. The Raspberry Pi can run a web server to communicate the data to a browser or application on a computer or smartphone.

Electronics used to test: Raspberry Pi, 220V 30A SSRs, 1-wire DS18B20 digital thermometer, 4.7k resistor. The output plug directly controls a solid state relay (ssr) which connects to a heating element. For wireless a Asus USB wifi dongle is used.

Information on Raspberry Pi low-level peripherals:
http://elinux.org/RPi_Low-level_peripherals

The language for the server side software is Python for rapid development. The web server/framework is web.py. Multiple processes connected with pipes to communicate between them are used. For instance, one process can only get the temperature while another turns a heating element on and off. A third parent temp control process can control the heating process with information from the temp process and relay the information back to the web server.

On the client side jQuery and various plugins can be used to display data such as line charts and gauges. Mouse overs on the temperature plot will show the time and temp for the individual points. It is currently working in a Firefox Browser.

jQuery and two jQuery plugins (jsGauge and Flot) are used in the client:
http://jquery.com
http://code.google.com/p/jsgauge/
http://code.google.com/p/flot/

The PID algorithm was translated from C code to Python. The C code was from "PID Controller Calculus with full C source source code" by Emile van de Logt An explanation on how to tune it is from the following web site:
http://www.vandelogt.nl/htm/regelen_pid_uk.htm

I have removed PID tuning for the moment, I'll add it back in once I've updated the code

This now uses a configuration file, the default config file (created on first load) will detail how to setup the config file

To add a probe use the value in /sys/bus/w1/devices/