Group Assignment :

Link

I working with Blynk’s Virtual Pins for remote control.

Managing Wi-Fi and authentication for cloud connectivity.

Designing reliable cloud-to-device message systems.

Understanding real-time feedback and latency in IoT systems.

Individual Assignment :

Master and Slave

In a master-slave system, one device (the master) controls one or more other devices (the slaves), which respond to the master's commands but do not initiate communication on their own.

For this assignemnt I plan to develop a code for LED ON, whenever I give the switch on it will glow other than it will off.

Transmitter code

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

typedef struct {
  bool buttonPressed;
} joystickData;

joystickData dataToSend;

uint8_t receiverMAC[] = {0x18, 0x8B, 0x0E, 0x93, 0xA3, 0xC4};  // Replace with receiver MAC

const int swPin = 2;  // Joystick button pin

void onSent(const uint8_t *mac_addr, esp_now_send_status_t status) {
  Serial.print("Send Status: ");
  Serial.println(status == ESP_NOW_SEND_SUCCESS ? "Success" : "Fail");
}

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);

  pinMode(swPin, INPUT_PULLUP);  // Joystick button (active LOW)

  if (esp_now_init() != ESP_OK) {
    Serial.println("ESP-NOW init failed!");
    return;
  }

  esp_now_register_send_cb(onSent);

  esp_now_peer_info_t peerInfo = {};
  memcpy(peerInfo.peer_addr, receiverMAC, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;

  if (esp_now_add_peer(&peerInfo) != ESP_OK) {
    Serial.println("Failed to add peer");
    return;
  }
}

void loop() {
  // Button pressed = LOW → true
  dataToSend.buttonPressed = digitalRead(swPin) == LOW;

  Serial.print("Button: ");
  Serial.println(dataToSend.buttonPressed ? "PRESSED" : "NOT PRESSED");

  esp_now_send(receiverMAC, (uint8_t *)&dataToSend, sizeof(dataToSend));
  delay(200);
}

• esp_now.h is for ESP-NOW communication and WiFi.h is needed because ESP-NOW needs WiFi in station (STA) mode.

• uint8_t receiverMAC[] = {0x18, 0x8B, 0x0E, 0x93, 0xA3, 0xC4}; - This is the MAC address of the receiver ESP32. We should replace it with our receiver board’s MAC.

I upload this code to the Master microcontroller and check the serial monitor as well

Then write down the Recdeiver code for the output

Receiver code

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

typedef struct {
  bool buttonPressed;
} joystickData;

joystickData receivedData;

// List of LED pins
const int ledPins[] = {2,3,4, 5, 6,7,8,9,10, 20,21};  // GPIO4 = D2, GPIO5 = D3, GPIO10 = D10
const int numLeds = sizeof(ledPins) / sizeof(ledPins[0]);

void onReceive(const esp_now_recv_info_t *info, const uint8_t *incomingData, int len) {
  Serial.println("Data received");

  memcpy(&receivedData, incomingData, sizeof(receivedData));

  Serial.print("Button Status: ");
  Serial.println(receivedData.buttonPressed ? "PRESSED" : "NOT PRESSED");

  for (int i = 0; i < numLeds; i++) {
    digitalWrite(ledPins[i], receivedData.buttonPressed ? HIGH : LOW);
  }

  Serial.print("LEDs: ");
  Serial.println(receivedData.buttonPressed ? "ON" : "OFF");
}

void setup() {
  Serial.begin(115200);
  delay(1000);
  Serial.println("Receiver with multiple LEDs starting...");

  // Set all LED pins as output
  for (int i = 0; i < numLeds; i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], LOW);
  }

  WiFi.mode(WIFI_STA);

  if (esp_now_init() != ESP_OK) {
    Serial.println("ESP-NOW init failed!");
    return;
  }

  esp_now_register_recv_cb(onReceive);
  Serial.println("ESP-NOW Ready. Waiting for joystick button...");
}

void loop() {
  // Nothing here
}

After uploading it I check the status of Slave microcontroller

Conclusion

Learning outcomes

• Understood the concept of master-slave communication using ESP-NOW protocol with ESP32 boards.

• Successfully implemented the transmitter (master) to read a button press and send data wirelessly.

• Practiced struct-based data transfer over ESP-NOW, ensuring type-safe communication.

• Gained hands-on experience in wireless device-to-device communication without needing Wi-Fi networks.