Environmental Sensor Controller

Temperature and humidity sensor controller (Terminal) that periodically sends its data over LoRa, which then a Gateway that receives it, Publishes to a MQTT broker. This project started as a small project to improve my personal PiniCore-Embedded library, and to add some sensors to my Home Assistant system.

How it works

At least one Gateway should be installed in the vicinity of the Terminal controllers.

Terminal

1. Terminal wakes up
2. Reads the sensors
3. Packs the necessary data, battery %, temperature ºC and humidity %
4. Sends the payload over LoRa
5. Waits for a ACK reply up to a defined timeout
6. Receives an ACK reply
7. Goes to sleep until next sensor read

Gateway

1. Gateway is always listening for LoRa payloads from the Terminals
2. Receives the payload, validates that it is valid and sends an ACK reply
3. Unpacks the data and creates a MQTT message
4. MQTT message is then published in the status topic
5. Listens for next LoRa payload

Hardware

Terminal

• LILYGO / TTGO LoRa32 Display
  • version used during developemnt: T3_V1.6.1
• DHT11
  • Digital Humidity Temperature sensor
• Battery
  • 18650 Li-Ion

Gateway

• LILYGO / TTGO LoRa32 Display
  • version used during developemnt: T3_V1.6.1

Credentials

Sensitive information and credentials should be placed in a header file named secrets.hpp inside the src folder.

Here is an example on how to structure it:

//// --------------- WIFI ---------------- ////
#define WIFI_SSID "MyWifi"
#define WIFI_PASS "supersecretpassword"
//// ------------------------------------- ////

//// --------------- MQTT ---------------- ////
#define MQTT_SERVER "mymqtt.broker"
#define MQTT_PORT 1883
#define MQTT_USER "mymqtt_user"
#define MQTT_PASS "mymqtt_password"
//// ------------------------------------- ////

MQTT

Online status

Function: Gateway current online status
Topic: environment/sensors_async/v0/{gateway_serial}/up/lwt
Payload: 0 or 1
Parameters:

• gateway_serial: uint64_t, 64 bit positive value

---

Version

Function: Gateway current firmware version
Topic: environment/sensors_async/v0/{gateway_serial}/up/version
Payload: uint16_t, positive integer value
Parameters:

• gateway_serial: uint64_t, 64 bit positive value

---

Status

Function: Terminal status payload will be placed in this topic by teh receiving gateway
Topic: environment/sensors_async/v0/{gateway_serial}/up/status
Payload:

• radioId: uint64_t, 64 bit positive value, serial of the Terminal that sent the payload
• version: uint16_t, 16 bit positive value, firmware version of the Terminal that sent the payload
• rssi: int, negative value tht represents the signal strength in dB
• battery: ```uint8_t``, 8 bit positive value that ranges from 0 to 100 and represents the battery status of the Terminal
• temperature: int8_t, 8 bit value that has the temperature read by the sensor from the Terminal
• humidity: uint8_t, 8 bit positive value that has the humidity read by the sensor from the Terminal

Parameters:

• gateway_serial: uint64_t, 64 bit positive value

Payload example: 6,1,-83,74,22,68

• 6: Terminal identifier
• 1: Terminal firmware version
• -83: Signal strength received by the Gateway from the Terminal
• 74: Terminal battery percentage
• 22: Temperature read in ºC
• 68: Humidity read in %

---

TODO and/or WIP

• Terminal:
  • sleep function, duration might not be precise since board does not have RTC
  • wake up on a button press and display for a short amount of time the current sensor data, in the build in display
• Gateway:
  • encrypt credentials
  • admin topic to ask gateway some debug information
  • into topic to ask gateway for statistics like uptime, bytes sent/received, etc
• Standalone:
  • maybe??? by not using LoRa and using WiFi, with the cost of more battery usage, but for home use might be fine
• Common features:
  • WiFi AP that is active on reset button press, that runs a HTTP web server tht provides a configuration page, possible features:
    • config: credentials
    • ping nearby gateways and show then on a list with their signal quality
    • factory reset