Spark Core Powered Sous Vide
26 Apr 2014For my first foray into the world of Arduino, in particular the SparkCore (backed from their superb Kickstarter campagin) I decided to try and make a quick and easy "Sous-Vide" machine.
I have been interested in the concept of Sous-Vide cooking for a little while and with the combination of having an old slow-cooker, a shiny new Spark Core, the Spark Cloud and the number of tutorials on building a machine around the internet has lead to an appealing and simple project.
The actual components for the project surprised me in just how short it was:
- Slow Cooker
- Spark Core
- Relay Shield
- DS18B20 (with an additional 4.7k Resistor)
- Project Box
I have pulled libraries from a couple different places which were ported for use with the Spark Core
There are elements of the code and structure is based from various tutorials around the 'tubes and I have tried to attribute those as I used them.
The GitHub repo for the project is HERE
The code behind the sous-vide machine is based around the Arduino PID controller library. The controller requires several variables; a SetPoint (target temperature for the machine), Input (current temperature of the machine) as well as three other variables (Kp, Ki, Kd) which controls the speed and aggression of the controller in heating up the machine and as it approaches the SetPoint. These three values are currently hard-coded into the code and require required tuning for the specific slow cooker, though there is a Arduino PID AutoTune library which can generate the va0lues if needed. I am currently using Kp = 0.1, Ki = 150, Kd = 0.45 which work fairly well for me, however they could be tuned better in the future.
Creating a new PID controller
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);
Using the PID controller
myPID.Compute();
On calling the Compute() function the controller uses the various inputs described above to assign a value to Output which, in this scenario effectively controls whether the relay is off or on. If the output is above a certain value the relay is turned on, below the relay is turned off. The Compute() function gets called manually approximately 10 seconds.
I am currently getting around 3 degree variance, with the SetPoint at 65c the lowest temperature is set around 63.5c and then up to 66.5c. This difference is a little larger than I would like, so in the coming weeks I will tuning the machine again to try and decrease the large changes in temperature. The largest issue with the machine at the moment is that it takes a very very long time for the machine to reach the SetPoint.
Future Features:
- Pre-heating of machine, wanting to cook at 14:00 with the water at 70c. The machine ensures the water is ready at the correct time.
- Web API to simplify logging and storing of temperatures.
- Graphing of temperatures.
- Nice shiny simple interface to control the machine.
Whilst writing this up I come across Mellow which looks eerily similar to what I have been planning to do with my machine with future! I am unbelievably close to ordering one, if only they delivered internationally!