Introduction: The Autotub - Fully Automated Cloud Connected Monotub for Mushroom Cultivation

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About: A passionate, nerdy engineer with an affinity for great food and wine.

If you want to grow gourmet or medicinal mushrooms at home, the “monotub” is widely accepted as the best method for ease of use and yield. However, even with the best constructed monotubs, amateur mycologists can encounter many issues including (but not limited to) lack of fresh air exchange during fruiting or contamination from lax sterile procedure in inoculation or spawning, or later when the tub needs to be opened for fresh air.

When I went looking for a commercially made Monotub, the Max Yield Bin one of the most markets products. The only thing is, its ~$70 USD and is simply a custom tote with holes. Then I was resolved to make something much better, and for cheaper. I wanted to have the most reliable results with the least manual effort, and hard data to make the best environmental decisions.

So that lead me to design and create a scalable, fully automated and cloud-connected monotub that provides multiple feature configurations which can include air filtration, powered CO2 exhaust fans, Temp/Humidity/Pressure/CO2 sensors, and lighting depending on the needs. It also records all of this data to the cloud and allows remote control and monitoring from an IoT mobile app.

Supplies

Recommended Tools:

  • High-Temp Hot glue gun
  • 1” and 2” hole saws
  • I used a 1-1/4” and a 2-1/8” hole saws which I had on hand, and are the largest you could use to fit the filters used in this project.
  • Soldering Iron
  • Heat shrink tubing & heat gun
  • Wire


I have arranged the parts list into 3 possible configurations. Each build upon the previous configurations functionality and provides more value but at a higher effort. I believe there is significant value added even if you just use the Autotub Basic config with a periodic timer controlling the fan system, without the lighting or IoT components when compared to the legacy methods.

Increasing Feature functionality: Autotub Basic->Advanced->Pro

Autotub Basic:

  1. ~50L Tote or tub - Gasket seal recommended ($18) - Home Depot
  2. Microppose filters - Microppose.com
  3. 4x 2” tub filters ($2 each)
  4. 2x 1” tub filters ($1 each)
  5. 12v Blower fan - 50x15mm ($2.50 each) - Amazon
  6. I used 2 of these in the guide, but one will work just fine.

Total Cost per Autotub Basic: ~ $30

Complexity: Easy


Autotub Advanced (Add-On):

  1. Temperature/Humidity/Pressure sensor - BMP280 (~$2 each) - Amazon
  2. LED 12v lighting - 2x T10 auto leds ($1.50 each) - Amazon (I had these on hand)
  3. 5v step-down converter ($1.50 each) - Amazon

Total cost per Autotub Advanced: ~ $35

Complexity: Moderate


Autotub Pro (Add-On):

  1. eCO2 sensor ($15 each) - Amazon

Total cost per Autotub Pro: ~ $50

Complexity: Moderate-Advanced


IoT Controller Infrastructure (Shared controller; 1 controller can support 1-4 Autotub Advanced):

  1. Arduino 33 IoT (~ $25) - Arduino
  2. 4-relay 5v board ($7) - Amazon
  3. Each Advanced Autotub needs 2 relays, so this supports 2 tubs)
  4. 12v power supply (1-2 Amps is sufficient) - Amazon
  5. Breadboard

Step 1: Selecting and Customizing Tub

Tub Selection

The traditional monotub can be created out of almost any tote of any size, however for this Autotub we are going to use a 50L fully sealed (waterproof) tub that is widely available at Home Depot. Since we are attempting to create a fully controlled environment, the gasket seal on the weather proof tub is important. We will be applying a negative pressure to pull fresh air in and exhaust CO2. When we apply a negative pressure with the blower fan, we want to be sure that the air coming into the tub is only entering through the filtered openings, and not through the edges of the lid which are not filtered.

EZY 50L IP67 Waterproof Tote @ Home Depot


Hole Cutting

We are going to use 2” Microppose tub filters for every air inlet, and a 1” filter with blower fan on each air exhaust. I chose 2” filters on the inlets to maximize filter surface area. With 4x 2” filters we get 12.56 sq inches of surface area, where if we used a 12x 1” filters, it would only be 9.42 sq inches. The 1” filter and hole is used for the blowers because it matches the blower fan inlet, maximizing the static pressure being pulled out of the tub.

I recommend using a hole saw or Dremel if possible. Spade type hole saws to not work well in plastic, as can be seen by my rough 1” holes in the photos.

Holes to cut:

  1. Cut 2 2” holes on each long side. Higher, toward the top edge
  2. Cut 1 1” hole on each short side. Lower, but at least 4” from the bottom to ensure space for substrate

Step 2: Basic: Attaching Microppose Filters

While you can use many different kinds of filter materials, on monotubs the recommendation has evolved from polyfill stuffed holes, to micropore tape, to Microppose filters over the years. I personally love the quality of the Microppose tub filters and their ability to maintain humidity, but their thickness has lead me to have trouble getting enough fresh air exchange (FAE) to fruit reliably via the passive or convective air exchange that worked for more open filters. IMproved airflow could be achieved with more holes and filter area, but since we want to have maximum control we will be using the blower fans to control airflow via a pull configuration through the filters.

You will need to deburr the melted plastic left behind from the hole saws with a sharp razor blade. I recommend doing this on the inside and outside edges of each hole so they are smooth when applying the filters from the outside and will not interfere with wiping down the inside in the future.

The Microppose filters come with a good adhesive already applied to the edges and you just need to pull them off and align them over the holes. Be sure the area around the hole is free from plastic debris or dust before sticking them down.

Step 3: Basic: Attaching Blower Fan

  1. Make sure you have attached the 1-inch Microppose filter directly over the blower fan inlet with its built-in adhesive.
  2. Apply a generous hot glue bead around the edges of the filter that you have attached to the fan.
  3. Looking from the inside of the clear tub, align the blower fan and filter to place over the 1” hole and hold in place until the hot glue cools.
  4. Use the hot glue to seal all around the edges of the fan (as pictured) to ensure it has an airtight seal through the filter and tub.

Note: I used 2 blower fans, one on each short side of the box. I am sure you could get away with just one on either side, but I liked the symmetry and I can run the both for shorter times. However, you MUST use a blower type fan, and not a normal radial PC fan. Blowers have much higher static pressure and can move air through the dense Microppose filters. A PC fan can not, I have tried this in a previous prototype of the Autotub pictured.

Step 4: Advanced: Attaching Lights

Mushrooms are not photosynthesizers, however they do need some amount of light to produce healthy fruits and grow in the right direction. Therefor this step might be optional for many people that might have enough ambient light in their monotub location that they do not need this additional lighting control.

I chose to use 12v LED lights I already had on hand which are made for autos and RVs. You can use any kind of LED lighting at 12v including white LED strips (which I have tried) or others made for cars interior lighting.

I soldered 2 bulbs in parallel and hot glued them above the blowers on either short sides of the Autotub.

Step 5: Advanced: Adding Temp & Humidity Sensor

The humidity and temperature sensor used in this project is the Bosch BMP280 combo sensor. It works on the I2C bus and has a different address than the CO2 sensor so they can be used on the same bus. When you purchase the BMP280 look for a breakout board that has a solder jumper to change the I2C address if you plan on controlling more than 1 Autotub.

Value Added: Once the BMP280 is installed, we will have the ability to log temp and humidity, but also trigger our exhaust fans while ensuring we don’t let humidity get too low. Likewise if we added a fogging humidifier, we could trigger it automatically when the Rh dips below 75%.

  1. Wire up the SDA and SCL I2C lines to the Arduino I2C bus.
  2. Wire up the GND, then VIN line to the 3.3v Arduino output
  3. Add the BMP280 Arduino library to your sketch if you have one started.

Step 6: Pro: Adding CO2 Sensor

The Autotub Pro adds a CO2 sensor into the mix, allowing auto venting of gas when the CO2 ppm reach a user-defined level during fruiting phases. No longer do you need to fan tubs manually or not know the exact CO2 levels and how much airflow you need.

The sensor used here is the CCS811, however the SGP-30 is a widely available alternative I2C CO2 sensor and either will work for this project.

  1. Wire up the SDA and SCL I2C lines just as you did for the BMP280 sensor in the previous step.
  2. WIre up the GND and 5V VIN lines
  3. Import the CCS811 library into your Arduino sketch.

Step 7: IoT Controller

The Autotub Pro (or up to 4 of them) is powered by the Arduino Nano 33 IoT. This new generation of natively cloud connected Arduino hardware paired along with the Arduino Cloud and Arduino IoT Mobile application makes development of connected data-driven devices a breeze. Once we have the readings from our sensors being updated as Arduino cloud variables, we can build custom dashboards as pictured within a couple clicks! Since we can also write variables back via the mobile app, we can remotely toggle “fruiting conditions” and define the threshold CO2 PPM before venting.