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README.md

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+# Nodemcu NTP clock with Max7219 LED matrix
+
+## Hardware parts
+
+* [Nodemcu v3 board](https://www.aliexpress.com/item/32565317233.html)
+* [MAX7219 Dot Matrix Module For Microcontroller 4 In One Display with 5P Line](https://www.aliexpress.com/item/32616345083.html)
+
+## Software dependencies
+
+This uses the Arduino IDE with the [esp8266 core](https://arduino-esp8266.readthedocs.io/en/2.6.3/installing.html#boards-manager) and the following libraries, installed using the Libraries manager:
+* [ezTime](https://github.com/ropg/ezTime) 0.8.3, to get time from NTP pool, properly format it and take in account timezones
+* [MajicDesigns's MD_MAX72XX](https://github.com/MajicDesigns/MD_MAX72XX) library 3.2.1, to write hours on the Max7219 LED matrix (this builds mostly upon [the MD_MAX72xx_PrintText](https://github.com/MajicDesigns/MD_MAX72XX/blob/25da52707cd3bbcc2406b9984d694afabecf6002/examples/MD_MAX72xx_PrintText/MD_MAX72xx_PrintText.ino) sample)

nodemcu-max7219-clock.ino

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+#include <ESP8266WiFi.h>
+#include <ESP8266WiFiMulti.h>
+#include <ezTime.h>
+
+ESP8266WiFiMulti wifiMulti;
+
+#include <MD_MAX72xx.h>
+#include <SPI.h>
+
+// Define the number of devices we have in the chain and the hardware interface
+// NOTE: These pin numbers will probably not work with your hardware and may
+// need to be adapted
+#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
+#define MAX_DEVICES 4
+
+#define DATA_PIN  14  // or MOSI (D5 on NodeMCU)
+#define CS_PIN    12  // or SS  (D6 on NodeMCU)
+#define CLK_PIN   13  // or SCK (D7 on NodeMCU)
+
+// SPI hardware interface
+//MD_MAX72XX mx = MD_MAX72XX(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);
+// Arbitrary pins
+MD_MAX72XX mx = MD_MAX72XX(HARDWARE_TYPE, DATA_PIN, CLK_PIN, CS_PIN, MAX_DEVICES);
+
+// Text parameters
+#define CHAR_SPACING  1 // pixels between characters
+
+// Global message buffers shared by Serial and Scrolling functions
+#define BUF_SIZE  6
+char message[BUF_SIZE] = "00:00";
+
+void printText(uint8_t modStart, uint8_t modEnd, const char *pMsg)
+// Print the text string to the LED matrix modules specified.
+// Message area is padded with blank columns after printing.
+{
+  uint8_t   state = 0;
+  uint8_t   curLen;
+  uint16_t  showLen;
+  uint8_t   cBuf[8];
+  int16_t   col = ((modEnd + 1) * COL_SIZE) - 1;
+
+  mx.control(modStart, modEnd, MD_MAX72XX::UPDATE, MD_MAX72XX::OFF);
+
+  do     // finite state machine to print the characters in the space available
+  {
+    switch (state)
+    {
+      case 0: // Load the next character from the font table
+        // if we reached end of message, reset the message pointer
+        if (*pMsg == '\0')
+        {
+          showLen = col - (modEnd * COL_SIZE);  // padding characters
+          state = 2;
+          break;
+        }
+
+        // retrieve the next character form the font file
+        showLen = mx.getChar(*pMsg++, sizeof(cBuf) / sizeof(cBuf[0]), cBuf);
+        curLen = 0;
+        state++;
+      // !! deliberately fall through to next state to start displaying
+
+      case 1: // display the next part of the character
+        mx.setColumn(col--, cBuf[curLen++]);
+
+        // done with font character, now display the space between chars
+        if (curLen == showLen)
+        {
+          showLen = CHAR_SPACING;
+          state = 2;
+        }
+        break;
+
+      case 2: // initialize state for displaying empty columns
+        curLen = 0;
+        state++;
+      // fall through
+
+      case 3: // display inter-character spacing or end of message padding (blank columns)
+        mx.setColumn(col--, 0);
+        curLen++;
+        if (curLen == showLen)
+          state = 0;
+        break;
+
+      default:
+        col = -1;   // this definitely ends the do loop
+    }
+  } while (col >= (modStart * COL_SIZE));
+
+  mx.control(modStart, modEnd, MD_MAX72XX::UPDATE, MD_MAX72XX::ON);
+}
+
+void setWifi() {
+  Serial.print("Connecting to wifi: ");
+  printText(0, MAX_DEVICES - 1, "WiFi");
+  WiFi.mode(WIFI_STA);
+  wifiMulti.addAP("XXX", "XXX");
+  wifiMulti.addAP("XXX", "XXX");
+  wifiMulti.addAP("XXX ", "XXX");
+  while (wifiMulti.run() != WL_CONNECTED) { // Wait for the Wi-Fi to connect: scan for Wi-Fi networks, and connect to the strongest of the networks above
+    delay(1000);
+    Serial.print('.');
+  }
+  Serial.println();
+}
+
+Timezone myTZ;
+void setClock() {
+  printText(0, MAX_DEVICES - 1, "NTP");
+  // Make ezTime show us what it is doing
+  setDebug(INFO);
+  // Wait for ezTime to get its time synchronized
+  waitForSync();
+  // See if local time can be obtained (does not work in countries that span multiple timezones)
+  if (myTZ.setLocation()) {
+    Serial.println(myTZ.dateTime());
+  } else {
+    Serial.println(errorString());
+    myTZ.setPosix(F("CET-1CEST,M3.5.0,M10.5.0/3")); // Europe/Paris
+  }
+  myTZ.setDefault();
+  Serial.println(myTZ.dateTime());
+  // Set NTP polling interval to 1 hour.
+  setInterval(60 * 60);
+}
+
+void setup() {
+  mx.begin();
+
+  Serial.begin(115200);
+  Serial.println();
+  setWifi();
+  setClock();
+}
+
+bool showColon = true;
+void loop() {
+  // Register ezTime events
+  events();
+  if (secondChanged()) {
+    showColon = !showColon;
+    char dateFormat[BUF_SIZE] = "H:i";
+    if (!showColon) {
+      strcpy(dateFormat, "H i");
+    }
+    printText(0, MAX_DEVICES - 1, dateTime(dateFormat).c_str());
+  }
+}