LoRa IoT Node System

ESP32-S3 IoT system for long-range event detection and wireless transmission using LoRa protocol.

---

Overview

This project implements a complete IoT system using two Heltec WiFi LoRa 32 V3 modules (ESP32-S3 + SX1262) communicating over LoRa at 915 MHz. A transmitter node detects motion events via a PIR sensor and sends structured packets to a receiver node, which validates data integrity and displays results on the integrated OLED screen.

Built entirely from scratch without external LoRa libraries — all SPI communication, packet protocol, and CRC16 validation are custom implementations.

---

System Diagram

graph LR
    subgraph TX["TRANSMITTER NODE - Heltec V3"]
        PIR["HC-SR501 PIR\nGPIO 7"] --> ESP_TX["ESP32-S3\nFreeRTOS"]
        BAT["LiPo 3.7V\nADC CH0"] --> ESP_TX
        ESP_TX --> OLED_TX["OLED SSD1306\nI2C"]
        ESP_TX -->|SPI| SX_TX["SX1262\n20 dBm"]
    end

    SX_TX -.->|"LoRa 915 MHz\nSF7 / 125kHz\n9-byte pkt + CRC16"| SX_RX

    subgraph RX["RECEIVER NODE - Heltec V3"]
        SX_RX["SX1262"] -->|SPI| ESP_RX["ESP32-S3\nFreeRTOS"]
        ESP_RX --> OLED_RX["OLED SSD1306\nI2C"]
    end

Loading

Software Layer Diagram

graph TD
    subgraph APP["app_main.c"]
        MAIN["xTaskCreate x3 TX / x2 RX"]
    end

    subgraph SVC["SERVICES"]
        EVT["event_service\nPIR queue\npkt build"]
        LORA_S["lora_service\nserialize\nsend/recv"]
        DISP_S["display_service\nOLED screens"]
        PWR_M["power_manager\nsleep FSM\nbatt check"]
    end

    subgraph DRV["DRIVERS"]
        PIR_D["pir_driver\nGPIO ISR"]
        LORA_D["lora_driver\nSPI cmds"]
        OLED_D["oled_driver\nI2C cmds"]
        PWR_D["power_driver\nADC + sleep"]
    end

    subgraph PROTO["SHARED PROTOCOL"]
        PKT["packet.h/.c\nbuild / serialize\ndeserialize / validate"]
        CRC["crc16.h/.c\nCRC16-CCITT"]
    end

    subgraph HAL["ESP-IDF v5.x + FreeRTOS"]
        HW["SPI / I2C / GPIO / ADC HAL"]
    end

    APP --> SVC
    SVC --> DRV
    SVC --> PROTO
    DRV --> HAL

Loading

---

Hardware

Component	Model	Notes
MCU	Heltec WiFi LoRa 32 V3 (ESP32-S3)	Both nodes
Radio	SX1262	Integrated in module
Sensor	HC-SR501 PIR	Transmitter only
Display	OLED 0.96" SSD1306	Integrated in module
Antenna	915 MHz	Integrated in module

Transmitter GPIO Map

Signal	GPIO	Type
LoRa SCK	9	SPI
LoRa MOSI	10	SPI
LoRa MISO	11	SPI
LoRa CS	8	SPI
LoRa RST	12	GPIO
LoRa IRQ (DIO1)	14	GPIO
LoRa BUSY	13	GPIO
PIR Sensor	7	GPIO INPUT
Battery ADC	1	ADC
ADC Control	37	GPIO
Vext	36	GPIO
OLED SDA	17	I2C
OLED SCL	18	I2C
OLED RST	21	GPIO

Receiver GPIO Map

Signal	GPIO	Type
LoRa SCK	9	SPI
LoRa MOSI	10	SPI
LoRa MISO	11	SPI
LoRa CS	8	SPI
LoRa RST	12	GPIO
LoRa IRQ (DIO1)	14	GPIO
LoRa BUSY	13	GPIO
OLED SDA	17	I2C
OLED SCL	18	I2C
OLED RST	21	GPIO

---

Architecture

lora-iot-node/
├── transmitter/               # TX node - detects PIR events and transmits
│   ├── main/
│   │   └── app_main.c         # FreeRTOS tasks: event, lora_tx, power
│   └── components/
│       ├── drivers/
│       │   ├── lora_driver    # SPI communication with SX1262
│       │   ├── pir_driver     # GPIO interrupt service routine
│       │   └── power_driver   # ADC battery + light/deep sleep
│       └── services/
│           ├── event_service  # Event queue and packet building
│           ├── lora_service   # TX packet serialization
│           ├── power_manager  # Sleep state machine
│           └── display_service# OLED TX screen layouts
├── receiver/                  # RX node - receives, validates and displays
│   ├── main/
│   │   └── app_main.c         # FreeRTOS tasks: lora_rx, display
│   └── components/
│       ├── drivers/
│       │   └── lora_driver    # SPI communication with SX1262
│       └── services/
│           ├── lora_service   # RX packet deserialization + CRC check
│           └── display_service# OLED RX screen layouts
└── shared/                    # Code shared by both nodes
    ├── protocol/
    │   ├── packet             # lora_packet_t struct + serialize/deserialize
    │   └── crc16              # CRC16-CCITT algorithm from scratch
    └── drivers/
        └── oled_driver        # SSD1306 I2C driver from scratch

---

Packet Protocol

Custom 9-byte packet with CRC16-CCITT integrity check:

typedef struct {
    uint8_t  node_id;        // Unique transmitter node ID
    uint32_t timestamp;      // Milliseconds since boot
    uint8_t  event_type;     // PIR_MOTION | HEARTBEAT | LOW_BATTERY
    uint8_t  battery_level;  // 0-100 %
    uint16_t crc;            // CRC16-CCITT of 7-byte payload
} lora_packet_t;

Byte	Field	Size
0	node_id	1 byte
1–4	timestamp	4 bytes
5	event_type	1 byte
6	battery_level	1 byte
7–8	CRC16	2 bytes

---

FreeRTOS Tasks

Transmitter

Task	Priority	Description
event_task	5	Reads PIR queue, builds lora_packet_t
lora_tx_task	4	Serializes and transmits packets
power_task	3	Manages battery and sleep states

Receiver

Task	Priority	Description
lora_rx_task	5	Receives and validates CRC
display_task	4	Updates OLED with packet info

---

Power Management

State	Current	Wake Source
Active TX	~150 mA	—
Idle	~25 mA	—
Light Sleep	< 2 mA	PIR interrupt
Deep Sleep	~150 μA	PIR or timer

WiFi and Bluetooth are disabled at boot — not required for this application.

---

Radio Settings

Parameter	Value
Frequency	915 MHz
Spreading Factor	SF7
Bandwidth	125 kHz
TX Power	20 dBm
Sync Word	0x12
Estimated Range	~10 km

---

Getting Started

Requirements

• ESP-IDF v5.x
• Two Heltec WiFi LoRa 32 V3 modules (ESP32-S3)
• HC-SR501 PIR sensor

Flash Transmitter

cd transmitter
idf.py build
idf.py -p PORT flash monitor

Flash Receiver

cd receiver
idf.py build
idf.py -p PORT flash monitor

---

Author

ronmart17 Embedded Systems Developer