Bridge

MQTT Radio Bridge

About

This program is used to join (or "bridge") the two MQTT brokers on the bike and the chase car so that MQTT messages may be sent without relying on being on the same local network.

At a high level, this works by making a subscription to all MQTT topics (#), and then for each received message:

1. Check the message was not one that was sent by the bridge itself (performed in the Bridge class),
2. Serialise the message into a series of bytes (performed in the TxProtocol class),
3. Pack the bytes into one or more Frames, or radio packets (also TxProtocol),
4. Send each of the Frames over the radio (using ZetaRfRadio).

On the other end of the bridge, the reverse process would happen.

5. A packet is received by ZetaRfRadio,
6. It is processed by RxProtocol, which will emit create a MQTT message when enough packets have arrived,
7. Bridge will register the message as one sent by the MQTT radio bridge, before finally,
8. The MQTT message is published using MqttBridgeClient.

Details on the protocol used for converting an MQTT message into bytes, and then into packets may be found on Notion.

Radio configuration

Radio configurations are stored in src/rf_config. The .xml file is for use in Silicon Labs' EZRadio Wireless Development Suite, which outputs a header file which is easily modified into the existing .h and .cpp files in the same directory.

Installation

1. If you did not clone submodules when cloning, run

   git submodule update --init

2. Install wiringpi:

   sudo apt install wiringpi

3. Download and install the Paho MQTT C library with (this can be done from any folder)

   git clone https://github.com/eclipse/paho.mqtt.c.git
   cd paho.mqtt.c
   git checkout v1.3.1
   
   cmake -Bbuild -H. -DPAHO_WITH_SSL=ON -DPAHO_ENABLE_TESTING=OFF
   sudo cmake --build build/ --target install
   sudo ldconfig

4. Install RF24 as per these instructions.
5. cd back to this Bridge directory, and run the following to configure and build.

   cmake .
   cmake --build . --config Release

   If lots of debug messages are desired, then Release may be relpaced with Debug. This will, amongst other things, print the bytes of every message sent or received.

Usage

You will need to have this repo installed on two Raspberry Pis.

On both Pis, once built (see above), start the executable with ./build/ZetaBridge.

Note: Currently, there are no configuration options for this project. If you wish to change the MQTT broker IP address, you must do so manually inside mqtt.cpp. By default, the client will connect to tcp://localhost:1883.