I'm not the first person to do this, but I wanted to document my specific method in case others find it useful.
I wanted a setup that could keep at least 20 spools of filament in a low-humidity (5-15%) environment.
The Sterilite 20 quart gasket box was chosen because it is popular for this purpose and fits my basic needs - it fits 4 spools of 1kg filament with minimal wasted space and the lid is gasketed.
I found a spool holder design on Printables by RCNet that uses 3/8" aluminum tubing, which can be bought in a coil and straightened, then cut to length and mounted between the endcaps to let four typical-size 1kg filament spools rest vertically in the box.
3A Molecular Sieve was chosen as the dessicant because it removes more water, faster than silica gel. It does take more heat/time to dry it back out than silica gel, but this should not be an issue if you have enough molecular sieve to rotate it.
I also wanted warnings/alarms for when the sieve granules needed changing, so the LOLIN D1 Mini was chosen as the microcontroller. They are cheap ($3.70 as of this writing), small, and fairly well designed.
Tangent: The current draw of each ESP8266 in this application is estimated at 70mA (they observe "periodic spikes" which, based on their observations, add up to about 3mA of that total) based on this research. This means that every six boxes consumes 420mA, or 50.4 watt-hours of energy a day - assuming I make no optimizations whatsoever to sleep in between polling periods. I could likely drop the average current for six sensors to 100mA with this optimization. They would then consume 22 times less power than my television's standby mode.
There is also an SHT30 shield for the D1 mini, which makes the sensor hookup simple. The SHT30 is a fairly accurate sensor (±2% RH) which will suffice for these purposes.
The firmware uses ESP_WiFiManager_Lite to simplify setup and configuration of the sensors. On first flashing, the sensor will go into Access Point mode with an SSID of dry_box_1 and the password drybox123. Connect to it, then navigate to http://192.168.4.1 in your browser. Set the WiFi credentials, device name, polling rate, humidity thresholds, and Discord webhook, then click Save. The device will reboot and start functioning. If you need to change configuration, "double-tap" the reset button on the microcontroller and wait a few seconds for a solid blue LED. This means that it is in Access Point mode again.
The link above is the official LOLIN Aliexpress store. If it becomes unavailable, you can find clones of it by searching "d1 mini v4" on Amazon.
The link above is the official LOLIN Aliexpress store. If this link becomes unavailable, you can use any SHT30 Breakout Board and wire it to a JST-SH1.0 4P connector. There is a receptacle labeled I2C on the bottom right of the D1 Mini v4 which accepts this connector.
You need one of these for each dry box, to power the sensor inside.
In case the Amazon link above stops working, this is what you're looking for:
These are for the sensor holders.
Amazon currently offers 6, 12, 18, and 24 packs. If this listing becomes unavailable, try Target, Walmart, or Home Depot.
This will be cut to 325 mm (12.75 inch) sections to act as the spool holders.
The 2 pound size would provide for ~150 grams of sieve per box, in a six box setup.
This is an estimate for a 24-spool, six box setup based on prices I paid in June 2024.
| Parts | Net Cost |
|---|---|
| D1 Mini | $23 |
| SHT30 Shield | $18 |
| USB Cable | $12 |
| Molecular Sieve | $18 |
| 20 qt Boxes | $54 |
| USB-C Breakouts | $5 |
| Threaded Inserts | $8 |
| Aluminum Tube | $25 |
| Total | $163 |
- Drill
- CA glue
- Glue Gun
- Soldering Iron
- Wire Strippers (12-24 AWG)
- Belt Sander (or sandpaper and patience)
- M2 Threaded Insert Tip for Soldering Iron
- 3/8" Tubing Straightener
- Metal Tubing Cutter
- Endcaps for aluminum tubing
- Dessicant tray
- Sensor mount