ESP32 LoRa Communication Module

#include <Arduino.h>
#include <SPI.h>
#include <Wire.h>
#include <LoRa.h>
#include <Keypad.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>


// Forward declarations
String shortNodeId();
String cropText(const String &text, uint8_t maxLength);
void drawComposer();
void commitPendingLetter();
String lettersForKey(char key);
void sendDraft();
void handleKey(char key);
void receiveMessages();

constexpr int LORA_SCK = 18;
constexpr int LORA_MISO = 19;
constexpr int LORA_MOSI = 23;
constexpr int LORA_NSS = 4;
constexpr int LORA_RESET = 27;
constexpr int LORA_DIO0 = 26;
constexpr int OLED_SDA = 21;
constexpr int OLED_SCL = 22;
constexpr int KEYPAD_R1 = 13;
constexpr int KEYPAD_R2 = 14;
constexpr int KEYPAD_R3 = 25;
constexpr int KEYPAD_R4 = 32;
constexpr int KEYPAD_C1 = 16;
constexpr int KEYPAD_C2 = 17;
constexpr int KEYPAD_C3 = 33;
constexpr long LORA_FREQUENCY_HZ = 865700000L;
constexpr uint8_t OLED_ADDRESS = 0x3C;
constexpr unsigned long MULTITAP_PAUSE_MS = 800UL;
constexpr uint8_t MESSAGE_LIMIT = 48;

Adafruit_SSD1306 display(128, 64, &Wire, -1);
const byte ROWS = 4;
const byte COLS = 3;
char keyMap[ROWS][COLS] = {
  {'1', '2', '3'},
  {'4', '5', '6'},
  {'7', '8', '9'},
  {'*', '0', '#'}
};
byte rowPins[ROWS] = {KEYPAD_R1, KEYPAD_R2, KEYPAD_R3, KEYPAD_R4};
byte colPins[COLS] = {KEYPAD_C1, KEYPAD_C2, KEYPAD_C3};
Keypad keypad = Keypad(makeKeymap(keyMap), rowPins, colPins, ROWS, COLS);

String draft;
String lastReceived = "No messages yet";
String statusText = "Type a message";
String pendingLetters;
char pendingKey = 0;
uint8_t pendingIndex = 0;
unsigned long lastKeyMs = 0;
uint32_t nodeId = 0;
bool screenDirty = true;

String shortNodeId() {
  return String(nodeId & 0xFFFF, HEX);
}

String cropText(const String &text, uint8_t maxLength) {
  if (text.length() <= maxLength) return text;
  return text.substring(text.length() - maxLength);
}

void drawComposer() {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("LoRa Chat  me:");
  display.println(shortNodeId());
  display.drawFastHLine(0, 10, 128, SSD1306_WHITE);
  display.setCursor(0, 15);
  display.print("Peer: ");
  display.println(cropText(lastReceived, 17));
  display.setCursor(0, 30);
  display.print("Write: ");
  display.println(cropText(draft, 18));
  display.setCursor(0, 45);
  display.println(statusText);
  display.setCursor(0, 56);
  display.print("*=erase  #=send");
  display.display();
  screenDirty = false;
}

void commitPendingLetter() {
  pendingKey = 0;
  pendingLetters = "";
  pendingIndex = 0;
}

String lettersForKey(char key) {
  switch (key) {
    case '1': return "1.,?";
    case '2': return "ABC2";
    case '3': return "DEF3";
    case '4': return "GHI4";
    case '5': return "JKL5";
    case '6': return "MNO6";
    case '7': return "PQRS7";
    case '8': return "TUV8";
    case '9': return "WXYZ9";
    case '0': return " 0";
    default: return "";
  }
}

void sendDraft() {
  commitPendingLetter();
  if (draft.length() == 0) {
    statusText = "Write something first";
    screenDirty = true;
    return;
  }

  String packet = "CHAT|" + shortNodeId() + "|" + draft;
  LoRa.beginPacket();
  LoRa.print(packet);
  int result = LoRa.endPacket();
  statusText = result == 1 ? "Sent" : "Send failed";
  draft = "";
  screenDirty = true;
}

void handleKey(char key) {
  if (key == '#') {
    sendDraft();
    return;
  }
  if (key == '*') {
    commitPendingLetter();
    if (draft.length() > 0) draft.remove(draft.length() - 1);
    statusText = "Erased";
    screenDirty = true;
    return;
  }

  String letters = lettersForKey(key);
  if (letters.length() == 0) return;
  unsigned long now = millis();
  if (key == pendingKey && now - lastKeyMs < MULTITAP_PAUSE_MS) {
    pendingIndex = (pendingIndex + 1) % letters.length();
    draft.setCharAt(draft.length() - 1, letters[pendingIndex]);
  } else {
    commitPendingLetter();
    if (draft.length() >= MESSAGE_LIMIT) {
      statusText = "Message is full";
      screenDirty = true;
      return;
    }
    pendingKey = key;
    pendingLetters = letters;
    pendingIndex = 0;
    draft += letters[0];
  }
  lastKeyMs = now;
  statusText = "Press again for letter";
  screenDirty = true;
}

void receiveMessages() {
  int packetSize = LoRa.parsePacket();
  if (packetSize == 0) return;

  String packet;
  while (LoRa.available()) packet += static_cast<char>(LoRa.read());
  if (!packet.startsWith("CHAT|")) return;

  int divider = packet.indexOf('|', 5);
  if (divider < 0) return;
  String sender = packet.substring(5, divider);
  String message = packet.substring(divider + 1);
  lastReceived = sender + ": " + message;
  statusText = "New message " + String(LoRa.packetRssi()) + "dBm";
  screenDirty = true;
}

void setup() {
  nodeId = static_cast<uint32_t>(ESP.getEfuseMac());
  Wire.begin(OLED_SDA, OLED_SCL);
  display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDRESS);
  drawComposer();

  SPI.begin(LORA_SCK, LORA_MISO, LORA_MOSI, LORA_NSS);
  LoRa.setPins(LORA_NSS, LORA_RESET, LORA_DIO0);
  if (!LoRa.begin(LORA_FREQUENCY_HZ)) {
    display.clearDisplay();
    display.setTextColor(SSD1306_WHITE);
    display.setTextSize(1);
    display.setCursor(0, 0);
    display.println("Radio not found");
    display.println("Check 3V3/GND and");
    display.println("radio signal wires");
    display.display();
    while (true) delay(1000);
  }
  LoRa.setTxPower(14);
  statusText = "Ready - type below";
  screenDirty = true;
}

void loop() {
  char key = keypad.getKey();
  if (key) handleKey(key);
  if (pendingKey && millis() - lastKeyMs >= MULTITAP_PAUSE_MS) commitPendingLetter();
  receiveMessages();
  if (screenDirty) drawComposer();
}