Balena "python-evdev2mqtt" Application

This is a Balena application consisting of 3 docker containers.

1. python-evdev2mqtt: this service is sending an mqtt message whenever a key is pressed/hold/released for a specific input device connected to one of the USB ports of a raspberry pi.
2. mqtt : mqtt broker receiving the mqtt messages sent by the python-evdev2mqtt service.
3. node-red: this service has a dual purpose:
   1. It demonstrates that python-evdev2mqttis working properly as it outputs those mqtt messages in the debug window of the node-red editor.
   2. It also demonstrates the (limited) features of the node-red-contrib-usbhid nodes that can also be used to receive events from those input devices connected to the USB ports of a raspberry pi.

Rationale for this Application

The idea is to create a micro service (= python-evdev2mqtt) that sends MQTT messages whenever a keyevent happens on an input device connected to a USB port of a raspberry pi device. Other services (e.g. node-red) by listening to those mqtt messages could then respond appropriately.

E.g. a numeric USB keypad can then be used to control the volume, switch radio channels, pauze, ...

Additional Features

1. Node-red editor can be accessed through the public device URL from the BalenaCloud dashboard.
2. It is also easy to create a hashed password for node-red by running the command "node-red-admin hash-pw" in a terminal window for the node-red service.

Hardware needed besides a raspberry pi

1. You need an USB device that generates key events (e.g. keypad, keyboard, ...)

SETUP INSTRUCTIONS

1. Deploy Balena application

So as you might have guessed this is indeed a balena application. So follow all standard instructions for setting up and deploying this balena application. (e.g. see Get started with Raspberry Pi 3 and Python and its github repository) After this step this balena application should be running on your raspberry pi.

2. TBD

3. Set Device Service Variables for the python-evdev2mqtt service

Within your balenacloud dashboard you can set the following device service variables for the python-evdev2mqtt container.

Service Variable	Description
input_device	This is the path of the input device that is connected to one of the USB ports of the raspberry pi. E.g. /dev/input/event1. Note that mqtt messages will only be sent for key events of this input device. At startup of the python-evdev2mqtt service all the connected input devices (with path) are written to the logs which you can view in the BalenaCloud dashboard.
mqtt_broker	default value = mqtt. This variable must be set if you want to use a different mqtt broker instead of the mqtt service
mqtt_port	default value = 1883. If the mqtt broker is listening to a different port then this variable must be set.

Interesting Links

1. python-evdev
2. python-evdev package also comes with a small command-line program for listing and monitoring input devices:

python -m evdev.evtest