Networking and Communications

Goals

For the group work this week, we have to:

Send a message between two projects. - Max Negrin, McKinnon Collins, and Yian Hu

To complete the assignment, we will be designing a telegraph using LEDs, buttons, and two ESP32-c3’s. Pressing the button on one ESP32 will light up the LEDs of both ESPs, allowing for transmission of text via Morse Code. Firstly, I have to find a protocol to enable communication between the two devices. I will be using the ESP-NOW protocol, and will follow this tutorial to establish communication, and Claude to generate the actual script that triggers the LEDs.

I used this script to find the MAC adress for each ESP32:

#include "WiFi.h"

void setup(){
 Serial.begin(115200);
 WiFi.mode(WIFI_MODE_STA);
 Serial.println(WiFi.macAddress());
}

void loop(){}

After connecting to the ESP32 via USB on the Arduino IDE and running this script, you should see something like this:

Then, I copied the MAC address from that MCU and put it in a google doc and labled it “1”. Then I ran it on the other ESP32, and also copied its MAC address. Now, with both of the addresses, I had Claude generate me the following script, which handles everything. You simply input the other ESP’s MAC address, and it will connect automatically. Then, when there is a signal in on the button’s GPIO, it sends a packet to the other ESP32 to tell it to light up its LED.

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

// --- Pin config ---
#define KEY_PIN   5    // Telegraph key (button), 3V3 to pin 5 (active HIGH)
#define LED_PIN   4    // LED, pin 4 to GND
#define BUZZ_PIN  6    // Buzzer, pin 6 to GND

// ESP 2's MAC address
uint8_t peerMAC[] = {0xE4, 0xB3, 0x23, 0xC6, 0xAD, 0x2C};

typedef struct {
  bool keyDown;
} TelegraphMsg;

TelegraphMsg outgoing;
TelegraphMsg incoming;
bool lastKeyState = false;

void onReceive(const esp_now_recv_info_t *info, const uint8_t *data, int len) {
  if (len == sizeof(TelegraphMsg)) {
    memcpy(&incoming, data, sizeof(TelegraphMsg));
    digitalWrite(LED_PIN, incoming.keyDown ? HIGH : LOW);
    digitalWrite(BUZZ_PIN, incoming.keyDown ? HIGH : LOW);
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(KEY_PIN, INPUT_PULLDOWN);  // Pull-down since button connects to 3V3
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZ_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  digitalWrite(BUZZ_PIN, LOW);

  WiFi.mode(WIFI_STA);
  WiFi.disconnect();

  Serial.print("My MAC: ");
  Serial.println(WiFi.macAddress());

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

  esp_now_register_recv_cb(onReceive);

  esp_now_peer_info_t peerInfo = {};
  memcpy(peerInfo.peer_addr, peerMAC, 6);
  peerInfo.channel = 0;
  peerInfo.encrypt = false;
  if (esp_now_add_peer(&peerInfo) != ESP_OK) {
    Serial.println("Failed to add peer");
  }
}

void loop() {
  bool keyDown = (digitalRead(KEY_PIN) == HIGH);  // Active HIGH

  if (keyDown != lastKeyState) {
    lastKeyState = keyDown;
    outgoing.keyDown = keyDown;
    esp_now_send(peerMAC, (uint8_t *)&outgoing, sizeof(outgoing));
  }

  delay(10);
}

Now that we got them connected to each other, we could start sending messages in Morse code. Mckinnon was sending me a message, and I had to decode it.

And here is another message, see if you can decode it.

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Last update: May 7, 2026