cec2rs232 0.4.0

Enables a Raspberry Pi to act as a bridge between CEC and RS-232 or IR

cec2rs232

Overview

This project aims to turn a Raspberry Pi into a bridge between the HDMI CEC standard and arbitrary control protocols for audio systems.

The intent is to automate powering up and controlling volume of certain hifi systems as you would a dedicated home theater receiver.

RS-232 and IR controls are supported. RS-232 requires a USB adapter, while IR can be controlled via GPIO.

Installation

It is assumed that the Raspberry Pi is not doing anything important so it is suitable to install cec2rs232 globally and run it as root. The package is available from pip:

sudo pip install cec2rs232

Copy cec2rs232.example.json to /etc/cec2rs232/cec2rs232.json. Edit it as needed.

Then you can have it run as a service using the provided systemd file:

sudo cp systemd/cec2rs232.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable cec2rs232
sudo systemctl start cec2rs232

This will start the process and ensure it starts again at boot.

Supported televisions

The intent is to support any TV with CEC capabilities. However, the project was originally developed using a Samsung TU7000 and therefore may unintentionally be designed against its quirks. Please report any problems you experience with another model of television and an attempt will be made to add support.

Supported audio devices

Cambridge Audio CXA61/81

These two integrated amplifiers support controlling power, source, and mute status over RS-232 but require IR for volume controls.

A 3.5mm TRS can be connected to the IR In port on the back of the amp instead of using an actual IR transmitter. In this case, connect the GPIO pin to the tip and ground to the sleeve. The ring need not be connected.

Driver name:

cambridge_cxa61

Parameters:

Name	Type	Description
serial_port	string	Path to serial device, e.g. "/dev/ttyUSB0"
ir_gpio_pin	integer	GPIO pin number driving the IR transmitter
tv_source	string (optional)	Source to activate when TV turns on, e.g. "D2". Omit to not change.

Others

Please feel free to make a pull request to add support for other devices.

CEC behavior options

Some options to handle device CEC implementation quirks are supported.

Name	Type	Description
echo_device_keypress	boolean	Default false. If true, resends playback device audio buttons.
ignore_device_keypress	boolean	Default false. If true, ignores playback device keypresses.

The two flags are independent, i.e., ignore does not disable echo.

The echo flag is helpful if your playback device sends broadcast CEC volume commands but your TV does not display visual feedback in that case. The command will be repeated with the TV as a specific destination.

The ignore flag is helpful in two cases. One, if you have a playback device which sends spurious keypresses that you wish two ignore. Second, if enabling the echo behavior has unintended consequences, such as the TV itself echoing the command to the audio device again (effectively double-pressing it).

MQTT

The controls for the connected audio device can also be exposed over MQTT, with the intention of being controlled from Home Assistant.

To enable this functionality, add an "mqtt" section to the configuration file:

"mqtt": {
    "server": "homeassistant.local",
    "port": 1883,
    "username": "mqtt",
    "password": "password",
    "name": "cxa61",
    "topic": "homeassistant/button/cxa61",
    "discovery": true
}

Each supported input (e.g., power_on, power_off, volume_up, volume_down, etc...) is exposed as a separate button entity, and when pressed will execute that command as if it were pressed on a remote control.

If not using Home Assistant, disable discovery. Then, you can manually send commands to the chosen topic.

Dependencies

Bindings for libCEC are required: sudo apt install python3-cec.

If using a virtual environment, specify --system-site-packages so the native libcec can be used.

Pigpiod is required: sudo apt install pigpiod && sudo systemctl enable pigpiod && sudo systemctl start pigpiod.

Other dependencies should be brought in automatically by pip.

License and attribution

Released under the terms of the MIT License.