DHT Sensor plugin

Summary

This plugin collects temperature and humidity from DHTXX sensors (usually connected to Raspberry Pi or similar host).

Configuration

Sample config (see plugin.conf in the repo):

[[inputs.dht_sensor]]

    # type of the sensor you are using (check your invoice if not sure).
    # possible values: "DHT11", "DHT12", "DHT22"
    sensor = "DHT22"

    # which data pin are you connectinmg to? 
    # Check your wiring if you are not sure
    data_pin = 4

    # number of retries in case of a failure
    number_of_retries = 3
    
    # also retry if a sensor returns data outside the sanity range.
    # temperature is specified in degrees celsius.
    retry_humidity_above = 100
    retry_temperature_above = 80 

Installation

• Clone the repo

git clone 

• Build the "dht_sensor" binary

$ go build -o dht_sensor cmd/main.go

NOTE: if you are building for Raspbery PI, you need to either:

1. Build it on the Raspberry Pi device itself, or
2. Cross-compile.

Usually (2) should be quite simple, but go-dht library has a portion of the code implemented in C, so you will need to install a cross compiler for ARM, and cross-compile using the following:

# compile the module for amd64.
$ go build -o dht_sensor.amd64 cmd/main.go

# install the debian package for cross-compilation. 
# You may need a different arch (i.e. eabi instead of eabihf) depending on your target HW or OS.
# Debian Bookworm on RPi3 needs as eabihf, while Bullseye was fine with eabi.
$ sudo apt install gcc-10-arm-linux-gnueabihf

# compile for ARM64 (RPi4)
$ env GOOS=linux GOARCH=arm64 go build -o dht_sensor.arm64 cmd/main.go

# compile for ARMv7l (RPI3b)
$ env CC=arm-linux-gnueabihf-gcc-10 CGO_ENABLED=1  GOOS=linux GOARCH=arm GOARM=7 go build -o dht_sensor.armv7l cmd/main.go

# compile for ARMv6l (RPI Zero)
$ env CC=arm-linux-gnueabihf-gcc-10 CGO_ENABLED=1  GOOS=linux GOARCH=arm GOARM=6 go build -o dht_sensor.armv6l cmd/main.go

(notice the extra CC and CGO_ENABLED variables required for ARM6/7 in addition to regular Go cross-compile flags). It is probably easier to compile directly on RPi, but some peopel do not like to install DEV dependencies in production.

• Edit the config
• Copy the binary and the config to an appropriate location

$ sudo cp plugin.config /etc/telegraf/telegraf-dht_sensor.config
$ sudo cp dht_sensor /usr/lib/telegraf/plugins/

• You should be able to call this from telegraf now using execd

[[inputs.execd]]
  command = ["/usr/lib/telegraf/plugins/dht_sensor", "-config", "/etc/telegraf/telegraf-dht_sensor.config" ]
  signal = "none"

• If you get an error Error during call C.dial_DHTxx_and_read(): failed to open GPIO export for writing, this means that the user you are running telegraf under does not have permissions to open /sys/class/gpio/export. To fix this, simply add your telegraf user into gpio group, and restart telegraf:

$ systemctl status telegraf 
[...]
Aug 02 14:43:59 pi telegraf[2419]: 2021-08-02T21:43:59Z E! [inputs.execd] stderr: "failed to gather metrics: Error during call C.dial_DHTxx_and_read(): failed to open GPIO export for writing"
$ ls -l /sys/class/gpio/export
-rwxrwx--- 1 root gpio 4096 Jul 31 20:17 /sys/class/gpio/export
$ sudo usermod -a -G gpio telegraf
$ sudo systemctl restart telegraf

Credits

• This self-contained plugin is based on the documentations of Execd Go Shim.
• This plugin uses a fork of Go-DHT library. Most of the heavy lifting is done there. Huge kudos to the authors.