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ESP-NOW is a wireless communication protocol based on the data-link layer that enables the direct, quick, and low-power control of smart devices without the need for a router. Espressif defines it and can work with Wi-Fi and Bluetooth LE. ESP-NOW provides flexible and low-power data transmission to all interconnected devices. It can also be used as an independent protocol that helps with device provisioning, debugging, and firmware upgrades.

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ESP-NOW is a connectionless communication protocol developed by Espressif that features short packet transmission. This protocol enables multiple devices to talk to each other in an easy way. It is a fast communication protocol that can be used to exchange small messages (up to 250 bytes) between ESP32 or ESP8266 boards. ESP-NOW supports the following features: Encrypted and unencrypted unicast communication; Mixed encrypted and unencrypted peer devices; Up to 250-byte payload can be carried; Sending callback function that can be set to inform the application layer of transmission success or failure.

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How is it different from existing protocols?

ESP-NOW is a wireless communication protocol that is different from Wi-Fi and Bluetooth in that it reduces the five layers of the OSI model to only one1. Additionally, ESP-NOW occupies fewer CPU and flash resources than traditional connection protocols while co-exists with Wi-Fi and Bluetooth LE.

Bluetooth is used to connect short-range devices for sharing information, while Wi-Fi is used for providing high-speed internet access2. Wi-Fi provides high bandwidth because the speed of the internet is an important issue.

Max Distance:

The range of ESP-NOW is up to 480 meters when using the ESP-NOW protocol for bridging between multiple ESP32s1. The range can be further increased by enabling long-range ESP-NOW. When enabled, the PHY rate of ESP32 will be 512Kbps or 256Kbps.

Maximum nodes:

ESP-NOW supports various series of Espressif chips, providing a flexible data transmission that is suitable for connecting “one-to-many” and “many-to-many” devices.

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Applications:

ESP-NOW is widely used in

  • smart-home appliances,
  • remote controlling,
  • sensors, etc.

In this tutorial, will see how to implement a basic ESP NOW communication between ESP32 Microcontrollers.

Step: 1

ESPNOW communication works based on the MAC address of the nodes. So, we need to find the Mac address of our slave or receiver node.

]For that just upload the following sketch to the ESP32 board and look for the Mac address in the serial monitor.

#include "WiFi.h"
 
void setup(){
  Serial.begin(115200);
  WiFi.mode(WIFI_MODE_STA);
  Serial.println(WiFi.macAddress());
}
 
void loop(){
}
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Once you uploaded the code, press the EN button and wait for the serial monitor results. It will show you the Mac address. Note that.

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Step-2:

Next, we need to prepare the transmitter, for that use this example sketch which can send multiple data types of data to the particular slave node.

#include <esp_now.h>
#include <WiFi.h>

// REPLACE WITH YOUR RECEIVER MAC Address
uint8_t broadcastAddress[] = {0x94, 0xB5, 0x55, 0x26, 0x27, 0x34};

// Must match the receiver structure
typedef struct struct_message {
  char a[32];
  int b;
  float c;
  bool d;
} struct_message;

// Create a struct_message called myData
struct_message myData;

esp_now_peer_info_t peerInfo;

// callback when data is sent
void OnDataSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("\r\nLast Packet Send Status:\t");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Delivery Success" : "Delivery Fail");
}
 
void setup() {
  // Init Serial Monitor
  Serial.begin(115200);
 
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);

  // Init ESP-NOW
  if (esp_now_init() != ESP_OK) {
    Serial.println("Error initializing ESP-NOW");
    return;
  }

  // Once ESPNow is successfully Init, we will register for Send CB to
  // get the status of Trasnmitted packet
  esp_now_register_send_cb(OnDataSent);
  
  // Register peer
  memcpy(peerInfo.peer_addr, broadcastAddress, 6);
  peerInfo.channel = 0;  
  peerInfo.encrypt = false;
  
  // Add peer        
  if (esp_now_add_peer(&peerInfo) != ESP_OK){
    Serial.println("Failed to add peer");
    return;
  }
}
 
void loop() {
  // Set values to send
  strcpy(myData.a, "I'm alive");
  myData.b = random(1,20);
  myData.c = 1.2;
  myData.d = false;
  
  // Send message via ESP-NOW
  esp_err_t result = esp_now_send(broadcastAddress, (uint8_t *) &myData, sizeof(myData));
   
  if (result == ESP_OK) {
    Serial.println("Sent with success");
  }
  else {
    Serial.println("Error sending the data");
  }
  delay(2000);
}
Note: Change the Mac Address here

Here are the serial monitor results, it show sent success but not delivered. Because we don't have the receiver.

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Let's try to implement the receiver.

Step-3:

Step-3:d example sketch which can receive the data from the master and it will print that into the serial monitor.

#include <esp_now.h>
#include <WiFi.h>

// Structure example to receive data
typedef struct struct_message {
    char a[32];
    int b;
    float c;
    bool d;
} struct_message;

// Create a struct_message called myData
struct_message myData;

// callback function that will be executed when data is received
void OnDataRecv(const uint8_t * mac, const uint8_t *incomingData, int len) {
  memcpy(&myData, incomingData, sizeof(myData));
  Serial.print("Bytes received: ");
  Serial.println(len);
  Serial.print("Char: ");
  Serial.println(myData.a);
  Serial.print("Int: ");
  Serial.println(myData.b);
  Serial.print("Float: ");
  Serial.println(myData.c);
  Serial.print("Bool: ");
  Serial.println(myData.d);
  Serial.println();
}
 
void setup() {
  // Initialize Serial Monitor
  Serial.begin(115200);
  
  // Set device as a Wi-Fi Station
  WiFi.mode(WIFI_STA);

  // Init ESP-NOW
  if (esp_now_init() != ESP_OK) {
    Serial.println("Error initializing ESP-NOW");
    return;
  }
  
  // get recv packer info
  esp_now_register_recv_cb(OnDataRecv);
}
 
void loop() {

}

Serial monitor results.

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Wrap Up:

We have seen how to implement the ESP NOW in ESP32 microcontroller, in upcoming tutorials will see how to transmit sensor data via ESPNOW.

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