I'm not the first person to think of this. This is a DIY 3d-printing filament dehydrator. For plastics like TPU it's important to make sure the filament has not had the opportunity to absorb moisture from the atmosphere
I know there are many commercial options for this. People like their vegetable dehydrators. I thought it would be a simple enough project to create a configurable software package for. Also, this is kinda just for fun. I wanted more software control over what is actually very simple hardware
This project is implemented in micropython for the Raspberry Pi Pico. It would mostly run on any other microcontroller that runs micropython EXCEPT for the pico-specific library rp2_dht_reader, which is a hardware-optimized implementation of a DHT11/DHT22 hydrometer library. If you instal the dht_reader that rp2_dht_reader is forked from you should be able to run this project on any micropython hardware, but that's largely untested.
The other exception is the use of the Pimoroni Pico display. It uses a custom firmware for the display: https://github.com/pimoroni/pimoroni-pico-rp2350/releases. Again, if you run with a different display or no display at all, this app should run just fine. But again, that's largely untested.
To run this application, you'll need to
- flash micropython onto your hardware https://github.com/pimoroni/pimoroni-pico-rp2350/releases for a display, or https://www.raspberrypi.com/documentation/microcontrollers/micropython.html#drag-and-drop-micropython for vanilla python
- install two dependencies by running install_deps.sh on your host computer with the device attached
- upload the python/ directory to the root of your device
- make sure to upload config.toml (vscode doesn't upload .toml files by default)
micropython runs main.py automatically. main.py reads config.toml and executes the main function specified there. There are a couple of more trivial test applications to make sure all the hardware works as expected. Pinouts and other parameters are specified there as well.
I'm using a Raspberry Pi Pico, and a Pimoroni Pico Display 2.8". The software is largely vanilla micropython, but there's two components that require this exact hardware configuration. The DHT humidity sensor uses the Pico's programmable hardware interface, and the firmware uses
Other off- a PTC heater, and 2 DC fans. One fan is a recirculation fan, and the other is an exhaust fan. The whole algorithm is to heat the drybox to a specified temperature, hold until enough moisture has been absorbed from things in the container, and then exhaust the now-humid air and replace it with outside air. It seemed like such a simple idea that I hope it can be used easily with many hardware projects.
Currently I am using some development modules. My main hardware is, very simply, https://github.com/stefansjs/schematics/tree/main/transistor_breakout_smd. That board requires a power supply that matches the other elements. My fans are 12-volt fans, so I need a 12-volt supply connected to that board, and 5V attached to the Pico.
It's currently a bit in a state of if-you-know-you-know. I'll provide better details once I have a more mature reference implementation