ESP-NOW Wireless Communication for ESP32

A minimal, production-ready implementation of ESP-NOW wireless communication using ESP-IDF v5.4.1 with FreeRTOS task architecture.

Overview

This repository contains two programs that demonstrate bidirectional struct-based data transmission between ESP32 devices using Espressif ESP-NOW protocol. ESP-NOW provides low-latency, connectionless communication without requiring WiFi router infrastructure.

Features

• Struct-based data transmission: type-safe communication using custom data structures
• Broadcast or direct transmission: support for both peer-to-peer and broadcast modes
• MAC address validation: automatic sender identification and packet validation
• Production-ready error handling: comprehensive logging and error reporting

Repository Structure

esp-now-communication/
├── transmitter/
│   ├── main/
│   │   └── main.c          # ESP-NOW transmitter with RTOS task
│   └── CMakeLists.txt
├── receiver/
│   ├── main/
│   │   └── main.c          # ESP-NOW receiver with RTOS task
│   └── CMakeLists.txt
└── README.md

Hardware Requirements

• 2x ESP32 development boards (ESP32, ESP32-S2, ESP32-S3, or ESP32-C3)
• USB cables for programming and power

Software Requirements

• ESP-IDF v5.4.1
• Python 3.x (for ESP-IDF tools)

Quick Start

1. Clone and Setup

git clone https://gitea.techquadbit.net/alex/ESP32_ESP-IDF_espnow.git
cd ESP32_ESP-IDF_espnow
. $IDF_PATH/export.sh  # Setup ESP-IDF environment

2. Flash Receiver

cd esp32_espnow_receive
idf.py set-target esp32  # or esp32s3, esp32c3, etc.
idf.py build flash monitor

Important: Note the MAC address printed in the monitor output.

3. Update Transmitter MAC Address

Edit esp32_espnow_transmit/main/main.c and replace the broadcast MAC address:

static uint8_t receiver_mac[] = {0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF}; // Your receiver's MAC from the Step #2

4. Flash Transmitter

cd ../esp32_espnow_transmit
idf.py set-target esp32
idf.py build flash monitor

Data Structure

The example transmits sensor data with the following data struct:

typedef struct {
    int node_id;
    float sensor1;
    float sensor2;
    uint32_t timestamp;
} data_t;

You may customize this structure for your specific application needs.

Configuration

Transmission Rate

Adjust the delay in espnow_send_task():

vTaskDelay(pdMS_TO_TICKS(2000)); // Send every 2 seconds

Queue Size

Modify queue depth in receiver for higher data rates:

espnow_queue = xQueueCreate(10, sizeof(espnow_event_t)); // 10 items

Task Priority

Change task priorities based on your system requirements:

xTaskCreate(espnow_send_task, "espnow_send", 4096, NULL, 5, NULL); // Priority 5

Communication Modes

Broadcast Mode (Default)

static uint8_t receiver_mac[] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};

Sends to all nearby ESP-NOW devices.

Direct Mode (Recommended)

static uint8_t receiver_mac[] = {0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF};

Sends to a specific device by MAC address.

Architecture

Transmitter Flow

• Initialize WiFi in Station mode
• Initialize ESP-NOW and add peer
• Create RTOS task for periodic transmission
• Send callback confirms delivery status

Receiver Flow

• Initialize WiFi in Station mode
• Initialize ESP-NOW with receive callback
• Create queue for ISR-to-task communication
• Receive callback validates and queues data
• RTOS task processes data from queue

Performance

Latency: < 10ms typical

Range: Up to 200m line-of-sight (environment dependent)

Data rate: Up to 250 packets/second

Payload: Up to 250 bytes per packet

Troubleshooting

No data received

Verify both devices are on the same WiFi channel

Check MAC address is correctly configured in transmitter

Ensure both devices use matching data structures

Packet loss

Reduce transmission rate

Increase queue size on receiver Check for WiFi interference

Build errors

Verify ESP-IDF version is v5.4.1 or later Ensure all components are properly linked in CMakeLists.txt

Contributing

Contributions welcome! Please submit pull requests or open issues for bugs and feature requests.