It uses rc_switch library for controlling wall sockets and receiving data from sensors. The library supports multiple protocols, the ones used by this gateway are:

Protocol 1, 2, 4, and 5 for wall switches
Protocol 2 for sensors
It can be extended to support more protocols

It works with 2 possible hardwares: Arduino Pro Mini and ESP8266 (currently in use). The code specific to each microcontroller is activated using #define directive:

#if defined(ESP8266)
#include "huzzah.h"
#else
#include "pro-mini.h"
#endif

Serial communication using Arduino Pro Mini

It works with an Arduino Pro Mini 5v 16 Mhz, where the original bootloader has been replaced with Optiboot using this tutorial: https://andreasrohner.at/posts/Electronics/How-to-make-the-Watchdog-Timer-work-on-an-Arduino-Pro-Mini-by-replacing-the-bootloader/

It is used as a serial gateway communicating in JSON format, when connected to a Raspberry Pi running Home Assistant.

Mode of operation:

it receives commands in JSON format over serial and translates them into RC commands to be sent to wall switches: ON/OFF
it receives sates from sensors, or RC commands from RC remotes, and translates them into JSON, which is written on Serial to be consumed by HA

MQTT communication using ESP8266

It works with any ESP8266 board, an Adafruit Huzzah in this case.

It is used as a gateway communicating in JSON format with Home Assistant, by publishing and subscribing to topics on MQTT. Devices on Home Assistant side are configured automatically using MQTT discovery.

Mode of operation:

it receives commands over MQTT and translates them into RC commands to be sent to wall switches: ON/OFF
it receives sates from sensors, or RC commands from RC remotes, translates them into JSON and updates devices in HA by publishing messages on MQTT

Sensors

Sensors transmit state using Protocol 2, a 32 bit unsigned number.

Protocol structure

   STATE
     |
1010|1|101010101|1010101010101|10101
----|-----------|-------------|-----
TYPE|    VALUE  |     VCC     |  ID

where:

ID: uniquely identifies a sensor
TYPE: the type of the sensor, see bellow
VALUE: used for GENERIC, HUMIDITY and TEMPERATURE sensors
STATE: used for CONTACT sensor only; since it doesn't conflict with other sensor types, it uses one bit from VALUE
VCC: battery voltage, used to detect when batteries need to be replaced

Sensors types

enum SensorType : uint8_t {
	GENERIC = 4,
	HUMIDITY = 5,
	TEMPERATURE = 6,
	CONTACT = 7
};

Sensors IDs

enum SensorId : uint8_t {
	WINDOW1 = 1,
	WINDOW2 = 2,
	WATER_SENSOR = 3,
	TEMP_SENSOR = 4,
	LIGHT_SENSOR = 5,
	MOVEMENT_SENSOR = 6,
	OIL_SENSOR = 7
};

Devices

Servers room temperature

Type: TEMPERATURE

Value and voltage

{
  "sensor": {
    "id": 4,
    "diagnostic": {
      "voltage": 2.239
    },
    "temperature": 16.2
  }
}

Value only

{
  "sensor": {
    "id": 4,
    "temperature": 16.2
  }
}

Oil tank sensor

Type: GENERIC

Value and voltage

{
  "sensor": {
    "id": 7,
    "diagnostic": {
      "voltage": 4.282
    },
    "value": 13
  }
}

Presence sensor

Type: CONTACT

Value and voltage

{
  "sensor": {
    "id": 8,
    "diagnostic": {
      "voltage": 3.28
    },
    "value": 1
  }
}

Switches

Gateway receives remote commands over RC Switch and translates them into JSON.

Protocol 1

ON

{
  "rcSwitch": {
    "protocol": 1,
    "state": true,
    "group": "1",
    "channel": 1,
    "raw_value": 5571921
  }
}

OFF

{
  "rcSwitch": {
    "protocol": 1,
    "state": false,
    "group": "1",
    "channel": 1,
    "raw_value": 5571921
  }
}

Protocol 2

{
  "rcSwitch": {
    "protocol": 2,
    "value": 2650807673
  }
}

Other protocols

{
  "rcSwitch": {
    "protocol": 4,
    "value": 1234567890
  }
}

DHT

Reads local DHT11 sensor and outputs it into JSON.

{
  "dht11": {
    "temperature": 31.9,
    "humidity": 45
  }
}

Commands from Home Assistant

It receives commands in JSON format, over serial or MQTT, and executes them.

Protocol 1

ON

{
  "rcSwitch": {
    "protocol": 1,
    "group": "00001",
    "channel": 1,
    "state": true
  }
}

OFF

{
  "rcSwitch": {
    "protocol": 1,
    "group": "00001",
    "channel": 1,
    "state": false
  }
}

Protocol 2

{
  "rcSwitch": {
    "protocol": 2,
    "value": "10010110000000000001110101111001"
  }
}

Other protocols

{
  "rcSwitch": {
    "protocol": 4,
    "value": "010001101001100101110100"
  }
}