dryer_cntrl (for lack of a better name) is a low-cost, hands-free solution for controlling and automating the Creality Filament Dry Box 2.0.

The solution is based on RP2040-zero development board and relies on emulating movement of the encoder, the host circuit has no knowledge it is controlled by another microcontroller. The modification allows for controlling the dryer via UART. This makes the solution quite flexible, as it can be connected to any host (even to the printer) and easily automated if needed.

The solution has its purpose in remote 3D printer setup, to provide hands-free operation of the dryer.

Learn about how this project came to be from this blog post.

For the modification you'll need following components:

• RP2040-zero or its clone,
• 3x 220Ω resistors,
• some wire and heat-shrinks.

That's really it! If you're feeling fancy or just want to keep the solution "clean" you can print the mount for rp2040-zero I designed. Use some heat-resistant filament like ABS.

You can grab the newest firmware form releases tab on this repo or build the binaries yourself.

To build the firmware you'll need Arduino Ide and install Earle Philhower's arudino-pico Raspberry Pi Pico Arduino core in the board manager. Then select target board to RP2040-zero and use Export Compiled Binary under Sketch to create the firmware file. This will create build directory and .uf2 firmware file inside.

Plug the RP2040-zero to your PC while holding down "boot" button, or if you already got it connected, press and hold the boot button and single press reset at the same time. Doing any of the above will put the board into flash mode, and it'll be exposed as a flash drive on your system. Drag and drop the firmware file. When copied, the device will disconnect.

Warning! Everything I described below, you're doing at your own risk. I do not take responsibility for you breaking your device or hurting yourself! The PCB operates at mains voltage, make sure the device is disconnected from the outlet when disassembling or assembling the dryer. Run the device only if all core components are secured where they belong and don't put any part of your body inside the device when it's turned on!

Disconnect the device from the power outlet!

Start disassembling the dryer by removing 4 screws on the inside. The screws are marked on the picture below.

Then remove heat insulation from the front and the back to remove the cover. The insulation will get damaged during this process, so you'll need to buy yourself a new sheet and cut it to size.

With one hand gently pry on sidewalls, and with the other hand gently pull the cover up by the rollers. Prying is needed, as cover will likely get stuck on the heat isolation on the side walls.

NOTE: Do not look inside while removing the cover or cover your eyes with safety goggles!
The rollers are designed to pop out with enough force and can hurt your eyes or face if you're not careful.

Next step is to remove the core components.

Start by removing the fan. Unscrew the bolts holding the fan. You'll likely be unable to remove the fan connector as it is glued in place. You can skip unplugging it until the PCB is free, so the glue can be removed first. Move the fan aside, so you can access the latch that secures the screen ribbon cable.

Unsecure the ribbon cable by pulling the latch with our nail or a prying tool. The picture below shows the latch in open position as well as encoder connections between microcontroller and the encoder.

Remove the ribbon cable out of the connector.

Now unsecure the heater. The screws holding it down are accessible from the bottom of the device, and they are hidden under the big sticker. The heater connector is also glued in, so you can skip unplugging it until the PCB is free.

Remove two screws holding down the PCB. Remove the dial, and the encoder screw securing the PCB on the front, as shown in below picture.

All core components shall be free at this stage. Lay the device on it's side and gently pull out the components out of the case, so you can have better access to it. Remember they are still attached by wires!

Now you can unscrew the terminals but first take a picture of the PCB to know how the wires go back together! This will free the heating element.

Gently remove the glue from the fan and backlight connectors. I used knife to do so but something pointy like toothpick might work as well. Unplug the connectors.

All 3 core components (pcb, heater, fan) should now be separated and can be pulled out of the case.

The following picture shows how to wire RP2040-zero to the dryer PCB.

Note: 220Ω resistors should be soldered inline on the GPx pins.

Pin roles:

The detailed RP2040-zero pinout can be found on Waveshare wiki.

Note: I don't claim this is a perfect solution. Feel free to do this your own way.

To mount RP2040-zero, one can use the 3d-printable shelve mount I designed. The shelf must be printed from heat resistant material like ABS.

A 10x20mm hole must be cut in the case with rotary tool, where there no other components inside. Then the shelf can be glued from the outside, and the development board can be popped into the place.

Some pictures showing the solution can be found below.

The device when plugged to the computer should create virtual UART port. On Mac for example, the name of the device will be likely to have "cu.usbmodem" prefix. Any terminal emulator with UART support (like minicom) shall be sufficient for base operations.

The default baud-rate is: 115200.
Remember to disable hardware flow control.

$ ls /dev/cu.usbmodem*
/dev/cu.usbmodem1101
$ minicom -D /dev/cu.usbmodem* -b 115200

While the device can be operated from command line directly, the dryer can be further automated via custom shell script that would send commands and read the responses from UART.

The solution operates in shell mode. It prints back user input so enabling local echo is not needed. For every command send the device shall print either OK when command succeeded or ERR:<reason> if the command failed.

To verify the device is working send an empty line to the device, it shall respond with OK.

The detailed operation manual is embedded into the device. Send help command to learn the operation.

This project is distributed under BSD-3 license. Refer to LICENSE for more information.

This project is built on Earle Philhower's arduino-pico core (LGPL-2.1 licensed). The source code is not shared directly but built firmware naturally embeds the solution. The Arduino build system does not output object files. See LICENSE.LGPL-2.1.txt for more information.