Digital temperature and humidity reporting for the Raspberry Pi Pico, used to continuously monitor a server room at the Mechanical Engineering Campus of Leibniz University Hannover.
- Raspberry Pi Pico
- DHT22/AM2302 or DHT11 sensor
- Wires/Breadboard
- 3D-printed case (optional)
| Pi Pico Label | Purpose | DHT22 Pin |
|---|---|---|
| 3V3 | Power | 1 |
| GPIO 15 | Data | 2 |
| GND | Ground | 4 |
- Many variants of the DHT22/DHT11 will have four pins. The third pin is unused.
- A pull-up resistor can be used but is not required, as the DHT22 has its own built-in.
By copying main.py to the Pico's on-board flash memory, it is executed at every boot.
Standard DHT drivers were migrated to micropython-lib starting with MicroPython 1.19, so most tutorials on the internet regarding this sensor no longer work!
The dht package can be copied over serial or installed OTA by modifying and executing setup.py on an internet-connected Pi Pico W. The library is should be saved to internal flash at /lib.
A periodic timer is set to request sensor data every 3 seconds. The values are JSON encoded and printed over serial.1 The onboard LED will be on for the duration of this subroutine.
On most Linux hosts, the Pi Pico will be available under /dev/ttyACM0. The reading processes may need to part of the dialout group.
For an example implementation to read this data, see dht22-nagios.
If the wires are not soldered and knocked around, a connection may become flaky and a GPIO error can occur. Any errors when reading data are reported in the JSON's error attribute as a POSIX errno.
The 3D-Printed case can be used to mount the internals. It features a hook to hang the arrangement from the ceiling.
OpenSCAD is used to model, customize and compile the final STL.
Footnotes
-
Unfortunately, WPA2-EAP Networks such as eduroam are not supported very well by MicroPython at the moment. ↩