How I Automated My Mushroom Grow Room for Under $200

Growing mushrooms is deceptively simple until you realize that fruiting conditions are brutally specific. Oyster mushrooms want 85-95% humidity, 18-24C, and CO2 under 800 ppm. Manually misting and opening a fan three times a day gets old fast.

This is the story of how I automated a mushroom fruiting chamber using a Raspberry Pi, a handful of sensors, a humidifier, a fan, and LoopString — for a total hardware cost under $200.

The Setup

Hardware Bill of Materials

Raspberry Pi 4 — $45 (already owned, but budget included)
BME280 sensor — $5 (temperature + humidity + pressure)
MH-Z19B CO2 sensor — $20 (NDIR, accurate to 400-5000 ppm)
DS18B20 temperature probe — $3 (waterproof, for substrate monitoring)
2-channel relay module — $4 (for humidifier and fan)
Ultrasonic humidifier — $25 (modified with always-on switch)
120mm PC fan — $8 (fresh air exchange)
MicroSD card (32GB) — $8
Pi power supply — $10
Wire, connectors, enclosure — $15
Martha tent (grow tent) — $45

Total: ~$188

The Martha Tent

A "Martha tent" is the mushroom community's name for a clear plastic greenhouse tent used as a fruiting chamber. Mine is a 4-tier wire shelf wrapped in a clear plastic cover, with holes cut for the humidifier inlet and fan exhaust.

Wiring

Sensor Connections

BME280 (I2C):

VIN to 3.3V, GND to GND
SDA to GPIO 2, SCL to GPIO 3
Monitors ambient temperature, humidity, and pressure inside the tent

MH-Z19B (UART):

VIN to 5V, GND to GND
TX to GPIO 15 (RX), RX to GPIO 14 (TX)
Monitors CO2 concentration — critical for knowing when to ventilate

DS18B20 (1-Wire):

Data to GPIO 4 with 4.7k pull-up resistor
Inserted into the substrate bag to monitor internal temperature

Actuator Connections

Relay Channel 1 — Humidifier:

GPIO 17 controls the ultrasonic humidifier
Humidifier modified with the button taped to "always on" so the relay is the power switch

Relay Channel 2 — Exhaust Fan:

GPIO 27 controls the 120mm fan
Fan pulls fresh air through the tent and pushes out CO2-rich air

Software Setup

Step 1: Flash and Claim

I flashed the LoopString OS image to the MicroSD card using Raspberry Pi Imager, booted the Pi, and claimed it with a 6-character token from the LoopString dashboard. Total time: 5 minutes.

Step 2: Configure in the Configurator

I opened the Configurator and created a room called "Fruiting Chamber" with:

BME280 (ambient temperature, humidity, pressure)
MH-Z19B (CO2)
DS18B20 (substrate temperature)
GPIO Relay x2 (humidifier, exhaust fan)
Hysteresis controller for humidity

Step 3: Set Up Humidity PID

For humidity control, I chose a hysteresis controller rather than a full PID. Mushroom humidity control is more like a thermostat than a smooth process:

Setpoint: 90% RH
On threshold: Humidity drops below 87%
Off threshold: Humidity rises above 93%
Dead band: 3% to prevent rapid cycling

When humidity drops, the relay turns on the humidifier. When it reaches 93%, it turns off. Simple, reliable, and the mushrooms do not care about precision above 85%.

Step 4: Set Up Fresh Air Exchange

CO2 management is critical. Mushrooms produce CO2 as they grow, and concentrations above 1000 ppm cause long, thin stems and small caps.

I set up a scheduled automation rule:

Fan runs for 5 minutes every 30 minutes
Additional trigger: if CO2 exceeds 800 ppm, fan turns on regardless of schedule
Fan off when CO2 drops below 600 ppm

This gives the mushrooms regular fresh air while keeping humidity loss to a minimum.

Step 5: Deploy

One click. The Configurator generated the Node-RED flow, sent it to the Pi, and within 10 seconds I had live data streaming to my dashboard.

Results

The Dashboard

My mushroom dashboard shows:

Ambient temperature — Holding steady at 21C (room temperature)
Substrate temperature — 22C (slightly warmer from mycelium activity)
Humidity — Cycling between 87-93% with the hysteresis controller
CO2 — Peaks at 700 ppm between fan cycles, drops to 450 during ventilation
Humidifier status — Toggle showing on/off state with duty cycle tracking
Fan status — Shows scheduled and triggered run times

What I Learned

Humidity is the hardest variable. The humidifier fog cools the air, which temporarily raises relative humidity readings. I added a 30-second settling delay after the humidifier turns off before reading humidity again.

CO2 sensors need warm-up time. The MH-Z19B takes 3 minutes to stabilize after power-on. LoopString's Node-RED template handles this automatically by discarding early readings.

Alarm thresholds are essential. I set a critical alert at 30% humidity (humidifier ran out of water) and got an email notification at 2 AM. Refilled the reservoir and saved a flush of oyster mushrooms.

Cost Comparison

Commercial mushroom automation controllers start at $300-500 and usually only handle humidity. My $188 setup handles:

Temperature monitoring (ambient + substrate)
Humidity control with hysteresis
CO2 monitoring with automated ventilation
Scheduled fresh air exchange
Cloud dashboard accessible from anywhere
Alert notifications via email
Historical data and analytics

Scaling Up

I started on the free tier (1 device, 8 sensor slots). My fruiting chamber uses 7 slots (3 from BME280, 1 CO2, 1 substrate temp, 2 actuators). When I added a second tent for shiitake, I upgraded to the Starter tier ($7/month) for a second Pi and 16 sensor slots.

The LoopString pricing scales naturally with your grow operation:

Free — 1 tent, basic monitoring
Starter — 2 tents with full automation
Maker — 5 tents for a small commercial operation

Try It Yourself

Create a free LoopString account and use the Mushroom Fruiting Chamber project template in the Configurator. It pre-configures the rooms, sensors, actuators, and control logic described in this article. All you need to do is wire the hardware and deploy.