Arduino and Python code to synchronize many hardware clients on a local LAN network via UDP broadcasts.

synchronize_ethernet_clients_arduino.ino

/*
// python code for sync command
// sends sync broadcast to the network to trigger all devices to synchronize

import socket
import time

UDP_IP = "255.255.255.255"  # Broadcast IP address
UDP_PORT = 8888  # UDP port

def send_sync_command():
    message = "sync"

    # Create a UDP socket
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # Enable broadcasting on this socket
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)

    # Send the "sync" command
    sock.sendto(message.encode(), (UDP_IP, UDP_PORT))

    # Close the socket
    sock.close()

# Send the "sync" command every second
send_sync_command()
*/

#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>

byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEF};

EthernetUDP Udp;
unsigned int localPort = 8888;

const int NTP_PACKET_SIZE = 48;
byte byteBuffer[NTP_PACKET_SIZE];

#define LED_PIN PC13
#define END_STOP_PIN PA3
#define ENABLE_PIN PB8


boolean outputState = false;

unsigned long lastSyncTime = 0;
unsigned long blinkOffset = 0;

void setup() {
  Ethernet.init(PB9);  // Use PB9 as CS pin for W5500

  Serial.begin(9600);
  while (!Serial);
  delay(250);

  
  pinMode(LED_PIN, OUTPUT);
  pinMode(END_STOP_PIN, OUTPUT);
  pinMode(ENABLE_PIN, OUTPUT);

  digitalWrite(ENABLE_PIN, HIGH);
  
  pinMode(10, OUTPUT);
  digitalWrite(10, HIGH);

  Serial.println("Initialize Ethernet with DHCP:");
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
    while (true) {
      delay(1);
    }
  }

  Udp.begin(localPort);
  Serial.println("Waiting for sync");
}

void loop() {
  checkUDP();
  synchronizeLED();
}

void checkUDP() {
  int packetSize = Udp.parsePacket();
  if (packetSize) {
    byteBuffer[packetSize];
    Udp.read(byteBuffer, packetSize);

    if (strcmp((char*)byteBuffer, "sync") == 0) {
      lastSyncTime = millis();
      //Serial.println("LEDs synchronized!");
      outputState = true;
      blinkOffset = 0; // Reset the blink offset on synchronization
    }
  }
}

void synchronizeLED() {
  // Calculate the adjusted blink time based on the offset
  unsigned long adjustedBlinkTime = lastSyncTime + blinkOffset;

  // Check if it's time to blink
  if (millis() >= adjustedBlinkTime) {
    // Save the next blink time
    lastSyncTime = millis();

    // Blink the LED
    //outputState = !outputState;
    //digitalWrite(LED_PIN, outputState);
    //digitalWrite(END_STOP_PIN, outputState);

    digitalWrite(LED_PIN, HIGH);
    digitalWrite(END_STOP_PIN, HIGH);
    delayMicroseconds(50);
    digitalWrite(LED_PIN, LOW);
    digitalWrite(END_STOP_PIN, LOW);
    

    // Update the blink offset for synchronization
    blinkOffset = 10; // Assuming the LED blinks every 1000ms
  }
}