README.md

keep_it_cold

Multi-node ESP32 LoRa DS18B20 temperature monitoring network
by @tscofield

Features

• DS18B20 temperature sensor (accurate, waterproof)
• LoRa peer-to-peer sync: node list, temperature, alarms
• OLED display for local status
• Configurable via web interface (NodeID, WiFi, node management, time, alarm silence)
• REST API for integration
• Node-down and check-in alarm logic (with daytime buzzer only)
• Manual timekeeping: no Internet required!

Hardware Requirements

• ESP32 Dev Board
• SX1262 LoRa module (HiLetgo or similar)
• DS18B20 temperature sensor
• SSD1306 OLED display (I2C, 128x64)
• Passive buzzer
• Breadboard or PCB

Wiring Diagram

Pin Connections (default, see main.cpp)

ESP32 Pin	Device	Function
17	DS18B20	Data
21	OLED SDA	I2C Data
22	OLED SCL	I2C Clock
32	Buzzer	Alarm
5,19,27,18,14,26	LoRa	SPI + Control

        +3.3V
          |
   .------------------------------.
   |            ESP32 Module      |
   |------------------------------|
   |        [integrated LoRa/OLED]|
   |                              |
   |    GPIO21 (SDA) ------------+----> OLED SDA
   |    GPIO22 (SCL) ------------+----> OLED SCL
   |                              |
   |    GPIO5 (SCK) --------------+----> LoRa SCK
   |    GPIO19 (MISO) ------------+----> LoRa MISO
   |    GPIO27 (MOSI) ------------+----> LoRa MOSI
   |    GPIO18 (NSS) -------------+----> LoRa NSS
   |    GPIO14 (RST) -------------+----> LoRa RST
   |    GPIO26 (DIO0) ------------+----> LoRa DIO0
   |                              |
   |    GPIO17 -------------------+----> DS18B20 DATA
   |                              |
   |    GPIO32 -------------------+----> Buzzer +
   |                              |
   |    GND ----------------------+----> All GND pins
   '------------------------------'
          |         |           |
     DS18B20     OLED/LoRa   Buzzer
     (VCC/GND)   (VCC/GND)   (GND)

Setup

1. Flash each node with src/main.cpp.
2. Wire per the diagram.
3. Power up, connect to WiFi (default SSID: ESP32Probe, PASS: NodeID).
4. Access web UI at http://<device-ip>/.
5. Configure NodeID, WiFi, node list, time, alarms.
6. Add all expected NodeIDs to each node (via web UI, automatically syncs).
7. Each node broadcasts its temperature and listens for peers.

Web Interface

• Set NodeID, WiFi SSID/Password
• Add nodes to the peer list (syncs to all)
• Silence alarms for 1 hour
• Set system time (no Internet required)
• View current and peer temperatures
• REST API: /api/temps for JSON data

Alarms

• Node-down: If any peer fails to send heartbeat for 30s, alarm triggers.
• Check-in: If nobody has used the web UI in 24 hours, alarm triggers.
• Only buzzes during 8:00–20:00.
• All alarms can be silenced via web UI.

Timekeeping

• Set time manually via web UI or serial.
• ESP32 keeps time internally (millis + stored epoch).
• All alarm logic uses this local time.

Example Serial Commands

• SETNODEID:ABCDEF — Set NodeID
• SETWIFI:myssid,mywifipass — Set WiFi
• SETTIME:2025,09,11,14,00 — Set time (YYYY,MM,DD,HH,mm)

License

MIT