ESP8266 NodeMCU Heartbeat File Monitor - note that LED pin is reversed here

blink_perl_wifi.ino

/*
 * Heartbeat File Meter
 * by truckershitch
 *
 * Added blink limit to prevent runaway blinking on boot
 * Cleaned up loop and variables
 * 11/22/17
 * Appended Wifi code for esp8266 module
 * 04/19/18
 * 
 * based on
 * Numerical Echo
 * by Martijn
 * 22 Nov 2008
 *
 * and
 * WiFi UDP Send and Receive String
 * created 30 December 2012
 * by dlf (Metodo2 srl)
*/


#include <SPI.h>
#include <ESP8266WiFi.h>
#include <WiFiUdp.h>

int status = WL_IDLE_STATUS;
char ssid[] = "<ssid>"; //  your network SSID (name)
char pass[] = "<password>";    // your network password (use for WPA, or use as key for WEP)
//int keyIndex = 0;            // your network key Index number (needed only for WEP)

unsigned int localPort = 2390;      // local port to listen on

char packetBuffer[255]; //buffer to hold incoming packet
//char  ReplyBuffer[] = "acknowledged";       // a string to send back

WiFiUDP Udp;

const int blinkOn = 250;  // timeframe that the LED is switched ON
const int ASC_ZERO = 48; // ASCII for 0 (zero)

void setup() {
  //Initialize LED
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH); // strangely this is off
  
  //Initialize serial and wait for port to open:
  Serial.begin(115200);
  //while (!Serial) {
  //  ; // wait for serial port to connect. Needed for native USB port only
  //}

  // attempt to connect to Wifi network:
  while (status != WL_CONNECTED) {
    Serial.print("Attempting to connect to SSID: ");
    Serial.println(ssid);
    // Connect to WPA/WPA2 network. Change this line if using open or WEP network:
    status = WiFi.begin(ssid, pass);

    // wait 10 seconds for connection:
    delay(10000);
  }
  Serial.println("Connected to wifi");
  printWifiStatus();

  Serial.println("\nStarting connection to server...");
  // if you get a connection, report back via serial:
  Udp.begin(localPort);
}

void blink_led(int value) {
  int count = value - ASC_ZERO; // number of beats
  if (count <= 15) { // validate input
    for (int i = 1; i <= count; i++) {
      digitalWrite(LED_BUILTIN, LOW);    // LED on
      delay(blinkOn);
      digitalWrite(LED_BUILTIN, HIGH);    // LED off
      delay(blinkOn);
    }
    digitalWrite(LED_BUILTIN, HIGH); // LED off
    delay(4 * blinkOn); // LED off - pausing here
  }
}

void loop() {

  // if there's data available, read a packet
  int packetSize = Udp.parsePacket();
  if (packetSize) {
    Serial.print("Received packet of size ");
    Serial.println(packetSize);
    Serial.print("From ");
    IPAddress remoteIp = Udp.remoteIP();
    Serial.print(remoteIp);
    Serial.print(", port ");
    Serial.println(Udp.remotePort());

    // read the packet into packetBufffer
    //int len = Udp.read(packetBuffer, 255);
    int len = Udp.read(packetBuffer, 1);
    if (len > 0) {
      packetBuffer[len] = 0;
    }
    Serial.println("Contents:");
    Serial.println(packetBuffer);

    int val = int(packetBuffer[0]);
    Serial.print("Value of buffer: ");
    Serial.println(val);
    if (val > 0) {
      blink_led(val); // blink away
    }

    // send a reply, to the IP address and port that sent us the packet we received
    //Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());
    //Udp.write(ReplyBuffer);
    //Udp.endPacket();
  }
}


void printWifiStatus() {
  // print the SSID of the network you're attached to:
  Serial.print("SSID: ");
  Serial.println(WiFi.SSID());

  // print your WiFi shield's IP address:
  IPAddress ip = WiFi.localIP();
  Serial.print("IP Address: ");
  Serial.println(ip);

  // print the received signal strength:
  long rssi = WiFi.RSSI();
  Serial.print("signal strength (RSSI):");
  Serial.print(rssi);
  Serial.println(" dBm");
}