alsd

alsd utilizes the gpioals driver to measure ambient light intensivity with a light dependent resistor connected to a GPIO pin of a Raspberry Pi and distributes the measurements via MQTT.

This tool is based on and borrows some basic functionality from buzzd.

Prerequisites

GPIOALS driver

The gpioals module must be compiled and loaded for the current kernel (so that the device /dev/gpioals_device is accessible) and the hardware wired to the correct GPIO pins.

In order for for alsd to be able to access the device, you will either have to run alsd as root user or ensure that the device is accessible through some customized udev rules.

Configuration

On startup, alsd will try to read its configuration file alsd.json. It will try to find it in:

• the current directory
• the .config directory in the executing user's home
• in /etc

JSON structure

Please refer to the example configuration file that comes with alsd to adapt to your use case. The following parameters can be set at top level:

• device: The path to the gpioals character device (/dev/gpioals_device by default)
• rate: The measurement rate in milliseconds, note that and additional 1.000 ms will be added for preparation of the measurement. The default value of 14.000 ms should yield a measurement roughly every 15 seconds. Increase the rate value if you want to reduce the amount of measurements collected. Be careful when decreasing below the default: In dark environments each measurement can require a multiple seconds to complete.

The connection to the MQTT broker can be setup in the mqtt section:

• broker: IP address or server name of the MQTT broker, localhost by default - according to the paho-mqtt documentation URIs should work, too (e.g. mqtt://server:port) - but that does not work for me currently
• topic: The MQTT topic alsd should send the measured values for, alsd by default

Running alsd

Upon execution alsd will trigger periodic measurments and send the observed charging time as integer values with the configured MQTT topic. In bright environments one should receive low values. The darker the environment, the higher the measured values. If the light intensity falls below the detectable threshold, no measurements will be sent.