Envsensor

Environmental Sensor Server. Intended for Raspberry Pi's sampling temperature & humidity from the physical location using DHT11 or DHT22 (/AM2302) sensors and exposing the realtime data via HTTP.

There's two parts to the app, firstly it samples the sensor every so often (configurable) and keeps a record of the latest reading taken.

The second part is the webserver, which exposes the data as JSON at / and also for Prometheus at /metrics.

Usage

Install it on your RPi:

sudo apt install golang
GOPATH=$HOME/go go get -u github.com/caius/go-envsensor/cli/envsensor

Then you'll want to figure out which GPIO pin your sensor is connected to and which model of sensor you have (DHT22 is more accurate!)

# DHT22 with data connected to physical pin 12, BCM pin 18, GPIO.1
$HOME/go/bin/envsensor -sensor-pin 18 -sensor-version 22

See init/systemd.txt for an example Systemd unit file you can use to run it as a service (aka run on boot & restart if it crashes.)

Architecture

The sensor is sampled in a goroutine, controlled via DHTSensor. (This is split across three files, so it can be developed on a mac without the DHT library installed.) This is kicked off by a time.Ticker channel every delay seconds. Any successful reading is sent into the readings channel.

The other half of the process is the webserver, which has a reading stored in a variable and both the endpoint handlers just return the data in that variable. It listens to the readings channel, any reading received is wrapped to a CachedReading which then expires a minute after it was created.

License

Apache 2, see LICENSE for further details.