A library that provides automatic pairing functionality using ESP-NOW between ESP32 devices.

• Selectable Master/Slave roles at instantiation
• Automatic saving of pairing results to non-volatile memory (EEPROM)
• Functions for reading and clearing pairing data
• Simple API for ESP-NOW communication

1. Copy this library folder to the Arduino IDE libraries folder
2. Restart Arduino IDE

#include <ESPNowAutoPairing.h>

// For Master use
ESPNowAutoPairing espNow(MASTER);

// For Slave use
ESPNowAutoPairing espNow(SLAVE);

void setup() {
    Serial.begin(115200);
    espNow.begin();
}

ESPNowAutoPairing(DeviceRole role)

• role: Specify MASTER or SLAVE

Initialize the library. Call this in setup().

Start pairing mode.

Stop pairing mode.

Check if pairing is complete.

Return value:

• true: Paired
• false: Not paired

Get the paired MAC address.

Return value:

• Pointer to paired MAC address (6 bytes)

Clear saved pairing data.

Send data to paired device.

Parameters:

• data: Pointer to data to send
• len: Data size

Set user-defined receive callback function.

Parameters:

• callback: Function pointer called on data reception

1. Call startPairingMode() to enter pairing mode
2. Broadcast PAIR_REQUEST
3. Receive PAIR_RESPONSE from Slave
4. Send PAIR_CONFIRM to complete pairing

1. Call startPairingMode() to enter pairing mode
2. Wait for PAIR_REQUEST from Master
3. Send PAIR_RESPONSE when PAIR_REQUEST is received
4. Receive PAIR_CONFIRM from Master to complete pairing

typedef struct {
    uint8_t type;        // Message type
    uint8_t mac[6];      // Sender's MAC address
    uint8_t data[8];     // Additional data
} pairing_message_t;

• PAIR_REQUEST (0x01): Pairing request
• PAIR_RESPONSE (0x02): Pairing response
• PAIR_CONFIRM (0x03): Pairing confirmation
• NES_COMMAND (0x10): Normal data communication

⚠️ Important: Drawing operations with M5.Lcd inside ESP-NOW callback functions will cause memory violations.

• ESP-NOW callback functions execute in interrupt context
• M5.Lcd drawing operations internally perform task switching and memory allocation
• SPI communication conflicts may occur

// Manage data with global variables
pairing_message_t msg;
bool RCVD = false;

// Only minimal processing in callback function
void OnDataRecvUser(const uint8_t *mac_addr, const uint8_t *incomingData, int data_len) {
  if (data_len >= (int)sizeof(pairing_message_t)) {
    RCVD = true;
    memcpy(&msg, incomingData, sizeof(msg));
  }
}

// Safe drawing operations in main loop
void loop() {
  if(RCVD == true && PAIR_STATUS == PAIRED) {
    if (msg.type == NES_COMMAND) {
      // Safe drawing operations here
      M5.Lcd.printf("Received: %02X %02X...", msg.data[0], msg.data[1]);
    }
    RCVD = false;  // Reset flag
  }
}

See the examples folder for detailed usage examples:

• MasterAtomS3_M5Unified: Master side implementation using AtomS3
• SlaveM5StackS3_M5Unified: Slave side implementation using M5StackS3

• Appropriate screen display according to pairing status
• Screen clearing only on status changes (prevents flickering)
• Visual display of MAC addresses and transmitted/received data

• Master/Slave Common: Long press Button A (1 second) to start pairing mode
• Automatic pairing data clear function
• Real-time data transmission/reception display

• MAC address transmission every 2 seconds
• Communication in 8-byte data format
• Detailed logging via serial output

• Uses 7 bytes of EEPROM (6 bytes MAC address + 1 byte pairing status)
• Normal data communication is not performed during pairing mode
• Once pairing is complete, settings are retained even after power off
• Do not perform drawing operations in callback functions (causes memory violations)
• Tested with M5Unified library

This library is released under the MIT License.