Nerves.Leds

Simple API to drive leds exposed by linux /sys/class/leds. Designed for use with nerves, but works on any distribution of Linux that supports /sys/class/leds.

Configuration

Use config.exs to create a friendly name that maps to an entry in /sys/class/leds that make sense for your application.

An example configuration for the Alix 2D boards:

# in your app's config/config.exs:
config :nerves_leds, names: [
    power:     "alix:1",
    connected: "alix:2",
    alert:     "alix:3"
]

Usage

It's customary to bring the Nerves.Leds module into scope as "Leds", as follows:

alias Nerves.Leds

Now, we can turn an LED on using the name we configured:

Leds.set power: true

Or make it blink slowly:

Leds.set power: :slowblink

We can even set multiple states for multiple LEDs at once:

Leds.set connected: false, alert: :fastblink

Built-In LED States

In addition to true (on) and false (off) the following atoms provide predefined behaviors:

• :slowblink - turns on and off slowly (about twice a second)
• :fastblink - turns on and off rapidly (about 7.5 times a second)
• :slowwink - mostly on, but "winks off" once every second or so
• :hearbeat - a heartbeat pattern

Customizing states

The standard LED states are defined as @predefined_states near the top of lib/nerves_leds.ex. You can change or add to them using config.exs as follows:

config :nerves_leds, states: [
    fastblink: [ trigger: "timer", delay_off: 40, delay_on: 30 ],
    blip: [ trigger: "timer", delay_off: 1000, delay_on: 100 ]]

See the Linux documentation on sys/class/leds to understand the meaning of trigger, delay, brightness, and other settings.

Limitations, Areas for Improvement

• most but not all `/sys/class/leds features are currently implemented