DHT

Driver for DHT 11, DHT 22, and AM2302 temperature/humidity sensors

Installation

This ports the Adafruit Python DHT library C source to handle the pin reads.

Currently this is only supporting valid Nerves targets, but in the future will be available to use in any Elixir environment with GPIO (like rasbian).

For none supported platforms (like host machine, MacOS, etc), readings will still work but be randomly generated.

def deps() do
  {:dht, "~> 0.1"}
end

See the datasheets for more info:

• Adafruit DHT22/AM2302
• SparkFun DHT22
• Mouser DHT11

Usage

You need to specify the GPIO pin number and sensor type when taking a reading. The sensor type can be a string, atom, or integer representation of the target sensor:

iex()> DHT.read(6, :dht22)
{:ok, %{temperature: 22.6, humidity: 50.5}}

iex()> DHT.read(6, "dht22")
{:ok, %{temperature: 22.6, humidity: 50.5}}

iex()> DHT.read(6, 22)
{:ok, %{temperature: 22.6, humidity: 50.5}}

iex()> DHT.read(6, "22")
{:ok, %{temperature: 22.6, humidity: 50.5}}

DHT also supports polling at regular intervals which outputs :telemetry events:

• [:dht, :read]
  • message is a map with :temperature and :humidity keys
  • metadata is map with :pin and :sensor keys
• [:dht, :error]
  • message is a map with :error key containing the failure message
  • metadata is map with :pin and :sensor keys

The polling period defaults to 2 seconds, which is the minimum rate allowed for DHT sensors, but you can specify longer:

# Poll DHT22 on GPIO 6 every 30 seconds
iex()> DHT.start_polling(6, :dht22, 30)
{:ok, #PID<0.233.0>}

Once polling, you can attach to the read events view :telemetry.attach/4

defmodule MyWatcher do
  def inspect_it(a, b, c, d) do
    IO.inspect(a)
    IO.inspect(b)
    IO.inspect(c)
    IO.inspect(d)
  end
end

:telemetry.attach("im-attached", [:dht, :read], &MyWatcher.inspect_it/4, nil)

Or do whatever else it is that you cool cats 😸 do with telemetry 😉