Raspberry Pi controlled kiln (part 2)

Posted On 4 May 2024

In my previous post on making a raspberry pi controlled kiln I reached the point with a script running on my Raspberry PI to measure the temperature and manually switch on and off the kiln. On a first attempt I wasn’t able to make the master repo of jbruce (2024-04-04) work with my set up. Still some steps to make!

In the meanwhile I discovered on the web old forums and posts using the same repo for making a kiln controller. For instance in this thread on ceramicartsdaily.org Jason (jbruce) describes and discusses the steps in the process of making the kiln-controller. It’s lovely to see such a supporting network of ceramic enthousiastic people collaborating together to make it work.

Finding a solution for the MAX31856 thermocouple issue

In the same thread some people are sharing their struggles with a MAX31856 and a K-type thermocouple to run the kiln-controller. This could mean a few things:

Either I:

• need to adjust the code of the kiln-controller with my setup;
• need to look for alternative repos;
• need to find a fork or branch on github.com with working configurations for my setup.

Adjusting the code in the kiln-controller means quite some time investigation, which I don’t have. So this option was for me less doable.

Checking other alternative kiln controllers on github led me to quite some interesting projects:

• https://github.com/CurlyTaleGamesLLC/PyKiln : Great code, different setup with ESP32, no RPi. Not recently updated.
• https://github.com/JoshOlds/Kilncontroller : Matches the MAX31856, userbase not so big at the moment. Not recently updated.
• https://github.com/williamolyolson/pikiln : Doesn’t match the MAX31856, userbase not so big at the moment. Not recently updated.
• https://github.com/daharoni/kilnpi : Great code, doesn’t match the MAX31856, recently updated.

The repo by daharoni looks promising, though I need to work a bit to make the MAX31856 working. I will check the branches and forks on jbruce12000 repo first to see if there are other options. Nevertheless the code by daharoni is worth a try lateron.

Third option is to check the different forks and branches based on jbruce12000 resulted in following the traces of a group hardworking people with interesting progressions. I checked in the github network view which fork was recently contributed and matches the MAX31856. Most of the stablest forks depend on MAX31855 rather than the MAX31856.

One other option is to check the branches in jbruce12000 repo. Besides the master, there is also

Branch	Updated	Behind	Ahead	Pull request
master	2 years ago	Default	Default
blinka	5 months ago	2	112
heating-rate	2 years ago	2	85	#127
kiln-profiles	2 years ago	14	0
python3	5 years ago	208	0

The most recently updated branch is the blinka, with 112 commits ahead of the default master trunk. Also from the previous article I recognise the blinka library for the RPi, because it made the temperature measurements from the MAX31856 with the K type thermometer and the RPi work. This is a promising branch.

In this branch the ./test-thermocouple.py, ./test-output.py and ./gpioreadall.py are helpful scripts to check the wiring and working of the MAX31856 thermocouple. A quick test of the code showed good temperature readings. So I decided to use this branch.

Installing the blinka version of kiln-controller

The steps to install the blinka version of the kiln-controller are well described on kiln-controller/README.md

To make sure that I used the blinka branch I directly downloaded the zip file and followed the steps described. The next step is to wire the SSR and the transistor for making the SSR switch on and off according to the logic.

Wiring the transistor and SSR

This is the documentation for the BC547B NPN transistor to switch the Solid State Relay on or off.

Pin configuration with the collector, base and emitter pin

BC547B NPN transistor schematically.

With the transistor and SSR with fan connected the whole testwiring looks like this:

I will add a wiring scheme later when it has passed the testing stage.

To have the optimum way of heatingcurve compared to the scheduled profile it’s neccessary to run the kiln-tuner and fill in the PID values in the config.py file. Running the kiln-controller/kiln-tuner.py takes a while and runs smoothly.

With the PID values being tuned in I am up for a small video to show how far I have reached until this point:

Next step is still testing and then making a testrun with the PID values.