This repository contains Linux kernel module reading temperature and relative humidity data from multiple AM2301/AM2023 (DHT11/DHT21/DHT22) sensors simultaneously connected to Raspberry Pi via GPIO pins.
This kernel module is an evolution of a module presented on Blackwire Embedded blog. Compilation issues against proc_fs
were fixed and multiple sensors support added. It works stable with kernels: Linux rpi 5.15.32-v7l+ #1538 SMP Thu Mar 31 19:39:41 BST 2022 armv7l GNU/Linux
. It should work with other kernel versions as well unless some major API changes were done in the kernel.
Latest measurement data from connected sensors is available under /proc/multi-am2301
and can be displayed anytime using e.g. following command: cat /proc/multi-am2301
. For each connected sensor it contains parameters like:
temp_curr
- value of last temperature measurement in Celsius degreestemp_1m
- average value of temperature for last 1 minuteRH_curr
- value of last relative humidity measurementRH_1m
- average value of relative humidity for last 1 minutedate
- formatted measurement date and timetimestamp
- measurement timestamp (millis from Epoch)QUAL
- how many sensor read attempts were there and how many of them were successfull. Note: idling Raspberry Pi hasQUAL
more than 90% for each correctly connected sensor, however when CPU is fully loaded or lots of interrputs occure (e.g. when reading lots of data from serial communication etc.)QUAL
will drop down.
Kernel module sits inside module
directory. Example commandline script which logs temperature and humidity into sqlite database sits inside scripts
directory. This script can be invoked by system cron e.g. every 3 minutes.
- clone this repository
cd module
- in source file
decoder.c
findstatic int _pins[] = { 5, 6, 12};
array initialization and correct GPIO logical pin numbers according to your needs (don't use board physical pin numbers!) - please check
/lib/modules/VERSION/build
directory inMakefile
against your OS and correct if needed. Note: you need kernel headers present in your system to be able to build kernel modules. You may want to check project rpi-source - execute
make
sudo cp multi-am2301.ko /lib/modules/{VERSION}/kernel/drivers/
sudo depmod
- to load kernel module:
sudo modprobe multi-am2301
- to unload kernel module:
sudo modprobe -r multi-am2301
Additionally to load this kernel module on Raspberry Pi startup add multi-am2301
to /etc/modules
configuration file.
Have fun :)