Automatic Fan Control for Bento Box

Edit 26 Jan 24 - Added quick diagram to help people get started on the project.

For the latest revisions, please visit: https://github.com/gallowayk/FanControlForBentoBox

After printing out the Bento Box filtration model, I wanted a means to control the fans so they weren't on 24/7 and only enabled when high VOC content was present. Originally, I was only going to use a bimetal temp switch since the ambient internal temperature of the printer would only rise while printing ABS, PC, Nylon, etc. However, I wanted to take a more sophisticated approach while keeping costs low. 

• RPi Pico (any variant)
• 3.3V trigger opto-isolated relay https://www.amazon.com/dp/B07XGZSYJV 
• MS1100 gas sensor https://www.amazon.com/dp/B0BF4JDW26 
• 128x64px SSD1306 OLED screen https://www.amazon.com/gp/product/B0833PF7ML 
• LM2596S buck converter https://www.amazon.com/gp/product/B07QKHR6PY 
  • The buck converter must be adjusted to +5VDC or +3/3.3VDC

Hardware

• 2x M2x5 or M2x8 self-tapping screw
  • One for VOC sensor
  • One for RPi Pico
• 8x 4x2mm Magnets
• Various jumper wires
  • Helps to use male to female jumper wires
  • It also helps to have a Dupont connection/terminal kit and crimper; this will allow you to make your own wires of just the right length

Tools

• Soldering iron
  • TS100 is my go-to due to its rapid heating and cooling
• "Helping hands" for soldering
• Precision tool set
  • Ball-end hex keys can be used as well
• Ferrule crimper + ferrules
• Heatshrink 

Note: Please be sure to safely work on your electronics.

• Do not work on anything while power is connected
• Do your best to avoid inhaling the flux/solder fumes

Software

Please read through the entire program to acclimate yourself with the functionality!

Pin definitions can be easily changed at the top from those I chose to use.

• For those who haven't used Raspberry Pis for their own scripts, rename “VOC_CKT.py” to “main.py” and save to your RPi Pico.

When I have a bit more time, I'll create a full write up with instructions on how to connect everything. Until then, feel free to ask me questions. Please note, however, that I may not be able to respond quickly.

There are still some tweaks I'd like to make, so a revision may come at some point. I want to reduce the clutter in the electronics housing by utilizing integrated solutions or developing my own PCB with an RP2040 chip and on-board power handling.

The bottom-most section has been completely remodeled to house electronics for automatic fan control along with multiple vents. The fan duct was also remodeled allowing the fan wires to be routed through the duct out of sight. I also added some reverse vents in hopes that the lower faster moving air will help draw warm air out of the bay.