Raspberry Pi PID temperature controller for electric BBQ smokers written in Python
For smokers of the style sold by:-
Why and how?
After purchasing a GEM two tier smoker from a food show I wanted to use it to make Texas style low-and-slow smoked BBQ. Out of the box, these smokers are not suitable for this as left unchecked they will easily reach >250°C which is easily double what is needed for good BBQ. First I tried a pulled pork and controlled the temperature by periodically turning the mains on and off. This was tiresome for 6 hours and the temperature control was terrible. However the meat came out tasty at the end. I thought then about automating the process and smokerctrl was born.
The first attempt was a bang-bang controller which worked significantly better than manual intervention but, due to the very slow response time of the system, there was lots of over-/under-shoot and the temperature was really only controlled within a 20°C window. This first version just had a command line interface and logged to a .CSV file so you could analyse the smoke data after the event but not live.
The next effort, smokerctrl2, was started to try to implement a PID (Proportional-Integral-Differential) controller. Initially this was worse until I realised due to the slow response the P- and I-terms needed to be quite small but the D-term needed to be very large. I tacked on a web interface in flask and used Highcharts to plot the data as it ran. This controlled the temperature very well; within +/-5°C most of the time. It uses a 5s period slow PWM (pulse width modulation) signal to control the heating element and because I didn't want to mess with mains electricity it turns the element on and off using an 433MHz RF switch meaning the Raspberry Pi and low voltage electronics goes nowhere near 240VAC.
I have cooked pulled-pork and brisket very successfully achieving a decent bark, visible smoke ring and an authentic smoky flavour. A 3kg piece of brisket point smokes in about 6 hours.
- Raspberry Pi 3 Model B
- Remote Controlled Mains Switch. Set to group III switch 2.
- 433MHz RF transmitter
The following external libraries are required for smokerctrl2 to run:-
sudo python ./smokerctrl2.py
Needs to be run sudo in order for WiringPi to be able to set up the GPIO pins.
http://[address of Pi]:5000/
- Start - starts control system
- Stop - pauses control system, terminate as above after Stopping
- Smoker Temperature: ETI 810-076 DOT / ChefAlarm oven probe and clip
- Meat Temperature: ETO 810-071 DOT / ChefAlarm penetration probe
Schematic is in TinyCAD format and generated parts list is correct. My first attempt I built on breadboard but then I made it more permanent on a Adafruit Perma-Proto HAT for Pi Mini Kit
I am not affiliated with any distributors or manufacturers of electric smokers.
This project is not approved or authorised. Use at your own risk.