Signal K GPIO Beeper Plugin

A Signal K plugin that activates a piezo beeper attached to the Raspberry Pi GPIO header when a Signal K notification alarm condition exists (e.g. anchor dragging, etc).

The plugin checks notifications on the configured interval (default 1 sec), and if any "emergency", "alarm", or "warn" notifications exist, it will beep the beeper for the configured duration.

The plugin will ignore notications that do not have:

method: ["sound"]

and it will ignore notifications that have:

status: {
    silenced: true
}

The plugin assumes you are using an "active" beeper (no PWM required) attached to GPIO 17 (BCM numbering) by default.

Prerequisites

This plugin controls GPIO without any native addon dependencies, so it works with Signal K App Store installs (which run npm install --ignore-scripts).

It prefers gpioset (from the gpiod / libgpiod-tools package) to control the GPIO pin, and falls back to raw sysfs GPIO if gpioset isn't found. gpioset is required for Raspberry Pi 5 / CM5, since those boards have removed sysfs GPIO entirely.

• Raspberry Pi OS Bookworm and later (including Pi 5): gpioset is installed by default. Nothing to do.

• Older releases (Buster, some Bullseye images): you may need to install it manually:

  sudo apt update
  sudo apt install gpiod

  Verify it's available with which gpioset.

If gpioset isn't found, the plugin automatically falls back to sysfs GPIO. This works on older Pi models but not on Pi 5 / CM5. Check the plugin status in the Signal K admin UI to see which implementation is active.

Configuration

Interval

Number of milliseconds between checking notifications and issuing a beep if warranted (default is 1000 milliseconds).

Duration

Beep duration in milliseconds (default is 300 milliseconds).

GPIO Pin

The BCM GPIO pin number the buzzer is connected to (default is 17).

GPIO Chip

The gpiochip device name to use, e.g. gpiochip0 (default). Only used when gpioset is available; ignored when falling back to sysfs.

Testing your wiring

You can trigger a manual test beep without needing to raise a real alarm, by visiting (or curling) this URL while the plugin is running:

http://<your-signalk-host>:3000/plugins/signalk-gpio-beeper-plugin/test

This beeps for 5 seconds by default. To use a different duration, add a seconds query parameter (0.5–30):

http://<your-signalk-host>:3000/plugins/signalk-gpio-beeper-plugin/test?seconds=0.5

The response text confirms which GPIO implementation (gpioset or sysfs) was used, which is a quick way to check what your device fell back to.