A MicroPython greenhouse project can monitor air temperature and humidity, track moisture in a chosen growing medium, and automate a bounded task such as watering. The controller reads sensors and operates a fan, light, or pump through suitable driver hardware—not directly from a microcontroller pin. Treat this as a build pattern: board, wiring, sensor placement, thresholds, and load ratings must match your parts and growing conditions.
How the greenhouse controller works
The basic control path is sensor → MicroPython board → driver or relay → actuator. A local manual switch or other override lets you control an actuator without relying on the automatic loop. Define a safe response for failed or implausible readings; for irrigation, that commonly means stopping the pump rather than leaving it running.
Start with one useful job, such as monitoring conditions or watering when a calibrated moisture reading crosses a crop-specific threshold. A local control loop does not require Wi-Fi or a cloud dashboard. Networking can be added separately for remote monitoring, but it brings its own connectivity and security decisions.
Choose a MicroPython controller
Both ESP32 boards and Raspberry Pi Pico-series microcontrollers have MicroPython support. The right choice depends on the exact board variant, wireless needs, available I/O, pin mapping, and the peripherals your sensors require. MicroPython maintains an ESP32 quick reference; Raspberry Pi documents MicroPython for Pico-series boards.
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| Choice | Useful when | Checks before wiring |
|---|---|---|
| ESP32 board | You want an ESP32-based build, potentially with Wi-Fi for optional remote features. | Confirm MicroPython support for the exact variant, its pinout, which pins support ADC, and the voltage limits. On ESP32, ADC2 shares resources with Wi-Fi; analog reads from ADC2 while Wi-Fi is active raise an exception. Use a suitable ADC1 pin for an analog soil sensor if Wi-Fi will be active, and verify the board documentation. |
| Pico-series board | You want a MicroPython-capable Raspberry Pi microcontroller family and can select a board variant suited to the project. | Check the chosen board’s wireless capability, analog-input availability, pin mapping, electrical limits, and MicroPython support for the peripherals you intend to use. |
Do not assume a GPIO label or pin number is universal across boards. MicroPython’s ESP32 documentation directs users to board documentation for mapping logical and physical pins and notes that ESP32 variants differ. The same practical rule applies when planning a build around another family: check the selected board’s documentation and schematic.
Select sensors for the conditions you need to know
Air temperature and relative humidity
A DHT22/AM2302 measures temperature and relative humidity; it does not tell you whether the root zone needs water. MicroPython’s DHT tutorial says to call a DHT22 no more often than once every two seconds for the most accurate results. It gives a different cadence for DHT11—no more than once per second—and points readers to the device datasheet for its operating range. Follow the datasheet for the exact sensor you buy.
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Growing-medium moisture
A soil-moisture probe measures a local signal from the medium around its sensing area. A generic probe’s raw or scaled reading is not a universal plant-water percentage. Readings depend on the sensor, its placement, and the actual medium, so calibrate it in the growing medium you will use and choose thresholds for the crop and setup.
Optional light measurement
A BH1750 light sensor is one option if you want to add light monitoring. It is not required for basic air and moisture monitoring. A community ESP32/MicroPython greenhouse project includes a DHT22, capacitive soil sensor, BH1750, relay board, and pump with tubing among its design choices; that parts list is an example, not a comparative test or a validated recommendation.
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Gather the parts and check compatibility
Keep the first build small. Add actuators only after the sensors are reading reliably.
Core monitoring parts
- A MicroPython-compatible controller board selected for the required connectivity and I/O.
- An air temperature and humidity sensor, such as a DHT22/AM2302.
- A soil-moisture sensor suitable for the medium and its moisture exposure.
- A suitable power source, wiring, and any required interface components.
Parts for automation or expansion
- A relay or other driver matched to the actuator and its electrical load.
- A pump and tubing for irrigation, or a fan or light if those are the tasks you intend to automate.
- Optional light sensor, display, enclosure, or logging and network features.
Before connecting a sensor output to a board, confirm its voltage is safe for that board’s input. MicroPython’s ESP32 quick reference gives 3.6 V as the ESP32 input-pin absolute maximum. That is a limit, not a target operating voltage; check the exact board and sensor specifications rather than assuming a module’s output is compatible.
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A pump is an electrical load, not something to power from a GPIO pin. Use a separate power arrangement and a switching device rated for the pump’s specifications. Check the pump’s voltage and current requirements, the driver’s ratings, and the flow and head needed by your irrigation layout. The parts in the community greenhouse example do not establish a complete electrical-safety design. Enclose and route the hardware appropriately for a damp environment, and follow component documentation and applicable local requirements.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Build the control loop around measured behavior
Write the program as a recurring sequence: read sensors at suitable intervals, validate readings, decide whether action is needed, switch the driver, and record or display the result if desired. MicroPython’s ESP32 tutorial path provides an official starting point for ESP32 setup and peripheral use.
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- Read at an appropriate cadence. Respect the sensor’s sampling guidance; for a DHT22, allow at least two seconds between calls for the most accurate results. Soil readings can be collected on a cadence appropriate to your system rather than being treated as instantaneous truth.
- Calibrate the moisture signal in context. Place the probe as it will be used, observe its readings in the selected medium under conditions you understand, and establish what readings correspond to the watering state you want. Do not copy a threshold from another sensor, pot, or crop without checking it.
- Use a deadband (hysteresis). Set distinct start and stop conditions so small fluctuations around one threshold do not rapidly switch a pump or fan on and off.
- Bound each actuator run. Give a pump a maximum runtime, then stop it and recheck before another run. The appropriate duration depends on the pump, tubing, medium, and container; the cited sources do not establish a universal value.
- Handle errors explicitly. If readings are missing, invalid, or implausible, avoid making an uncontrolled watering decision. Put the output in its defined safe state and provide a way to inspect or override it.
There is no crop-independent moisture threshold or watering schedule established here. Choose setpoints for the crop and growing medium, then adjust them based on observed readings and plant conditions.
Commission the build before leaving it unattended
- Test sensor readings and actuator switching separately before combining them in automatic control.
- Verify the board pin mapping, sensor output levels, and driver connections against the exact component documentation.
- Test a pump with water safely contained; confirm it starts, stops, and respects the maximum runtime.
- Observe readings and control behavior over time before relying on automation, and keep the manual override accessible.
This approach keeps the project useful without implying that a particular parts list or threshold is a tested turnkey greenhouse. For a source example of an ESP32/MicroPython arrangement, see the author’s greenhouse project.
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