Kiln Controller

Inspired by https://github.com/jbruce12000/kiln-controller

Hardware I'm using

• Old Skutt K-1018: Craigslist
• High temperature Type K thermocouple (I got the 12 inch with 11 gauge wires): http://auberins.com/index.php?main_page=product_info&cPath=3&products_id=39
• 40a 240v contactor (with 240v coil): https://www.auberins.com/index.php?main_page=product_info&cPath=2_31&products_id=164
• Raspberry Pi Zero W: https://www.adafruit.com/product/3400 (although I bought mine from Microcenter)
• Small relay for driving the contactor: https://www.adafruit.com/product/3191
• Thermocouple amplifier: https://www.adafruit.com/product/269

Setting up Raspberry Pi

I'm using a Raspberry Pi Zero W.

Installing OS

1. Downloaded and unzipped Raspberry Pi OS (32-bit) Lite (kernel version 4.19) from here https://www.raspberrypi.org/downloads/raspberry-pi-os/
2. Flashed image to SD card using Etcher (the application is called balenaEtcher)
3. Removed and reinserted SD card then followed this tutorial to make it SSH-able via USB: https://desertbot.io/blog/ssh-into-pi-zero-over-usb (the ssh-keygen step didn't work, so I skipped right to SSH-ing which seemed to be ok)
4. Installed vim with sudo apt-get install vim
5. Installed git with sudo apt-get install git

Setting up CircuitPython

Followed these instructions: https://learn.adafruit.com/circuitpython-on-raspberrypi-linux/installing-circuitpython-on-raspberry-pi

1. I had to install pip3.
2. I didn't make python3 default.
3. I enabled both I2C and SPI (even though I think technically I'll only be using SPI).

I ran the blinkatest.py script they included at the end, and it worked!

Other necessary stuff

1. Installed drivers for thermocouple amplifier: pip3 install adafruit-circuitpython-max31855
2. Cloned this repository

Running script on startup

I used cron: https://www.raspberrypi.org/documentation/linux/usage/cron.md

Ran crontab -e then added @reboot python3 /home/pi/kiln-controller/control/temperature-readout.py &

Running script in background

I'm using nohup. Example command:

nohup python3 slow_04_bisque.py &> first_slow_bisque.txt &

Shutting down

sudo shutdown -h now

Issues (and solutions)

Connected a 1.5" OLED SSD1351 display (cheap one off Amazon) via SPI. I was using the luma.oled package to run it. It was updating extremely slowly, I'd see the scan lines slowly move down the display even when I was drawing text. I ran the luma perfloop.py example and it only achieved 0.25 FPS. At first, I thought there might be something wrong with my Raspberry Pi's SPI speed. However, I realized that I was running another python process which was reading from a thermocouple using SPI (using Adafruit's busio package). I killed this process, and, lo and behold, my display now updated much faster.