Smart Thermal Printing Calculator

#include <Arduino.h>
#include <Wire.h>
#include <WiFi.h>
#include <NimBLEDevice.h>
#include <Adafruit_MCP23X17.h>
#include <Adafruit_Thermal.h>
#include <Arduino_GFX_Library.h>
#include <lvgl.h>

#define LCD_B1 17
#define LCD_B2 18
#define LCD_B3 19
#define LCD_B4 20
#define LCD_G1 11
#define LCD_G2 12
#define LCD_G3 13
#define LCD_G4 14
#define LCD_G5 15
#define LCD_R1 2
#define LCD_R2 3
#define LCD_R3 6
#define LCD_R4 7
#define LCD_SPI_SCK 42
#define LCD_SPI_MOSI 47


// Forward declarations
void flushDisplay(lv_disp_drv_t *disp, const lv_area_t *area, lv_color_t *colorMap);
void initDisplay();
void initKeypad();
void printMockReceipt();
void onKeyPressed(uint8_t row, uint8_t col);
void scanKeypad();
void readFuelGauge();
void initConnectivityStubs();

constexpr int I2C_SDA = 8;
constexpr int I2C_SCL = 9;
constexpr int PRINTER_RX = 4;  // ESP32 input, connected after the 5 V-to-3.3 V divider.
constexpr int PRINTER_TX = 5;  // ESP32 output, connected to printer RX.
constexpr int LCD_DE = 38;
constexpr int LCD_VSYNC = 40;
constexpr int LCD_HSYNC = 39;
constexpr int LCD_PCLK = 21;
constexpr int LCD_R0 = 1, LCD_R1 = 2, LCD_R2 = 3, LCD_R3 = 6, LCD_R4 = 7;
constexpr int LCD_G0 = 10, LCD_G1 = 11, LCD_G2 = 12, LCD_G3 = 13, LCD_G4 = 14, LCD_G5 = 15;
constexpr int LCD_B0 = 16, LCD_B1 = 17, LCD_B2 = 18, LCD_B3 = 19, LCD_B4 = 20;
constexpr int LCD_SPI_CS = 41, LCD_SPI_SCK = 42, LCD_SPI_MOSI = 47;
constexpr uint16_t LCD_WIDTH = 320;
constexpr uint16_t LCD_HEIGHT = 960;
constexpr uint8_t MCP_ADDRESS = 0x20;
constexpr uint8_t MAX17049_ADDRESS = 0x36;
constexpr uint32_t PRINTER_BAUD = 19200;
constexpr uint32_t DEBOUNCE_MS = 30;

HardwareSerial printerSerial(1);
Adafruit_Thermal printer(&printerSerial);
Adafruit_MCP23X17 mcp;

// Replace these porch values with the timing table supplied for the exact panel glass.
Arduino_ESP32RGBPanel *rgbBus = new Arduino_ESP32RGBPanel(
  LCD_DE, LCD_VSYNC, LCD_HSYNC, LCD_PCLK,
  LCD_R0, LCD_R1, LCD_R2, LCD_R3, LCD_R4,
  LCD_G0, LCD_G1, LCD_G2, LCD_G3, LCD_G4, LCD_G5,
  LCD_B0, LCD_B1, LCD_B2, LCD_B3, LCD_B4,
  1, 40, 48, 40, 1, 13, 3, 29, 1, 16000000UL);
Arduino_ST7701_RGBPanel *gfx = new Arduino_ST7701_RGBPanel(
  rgbBus, GFX_NOT_DEFINED, 0, true, LCD_WIDTH, LCD_HEIGHT,
  st7701_type1_init_operations, sizeof(st7701_type1_init_operations), true,
  40, 48, 40, 13, 3, 29);

static lv_disp_draw_buf_t drawBuffer;
static lv_color_t *lvBuffer = nullptr;
static lv_disp_drv_t displayDriver;
static uint32_t lastTickMs = 0;
static uint8_t stableKeys[6][7] = {};
static uint8_t pendingKeys[6][7] = {};
static uint32_t changeTime[6][7] = {};

const char *const keyNames[6][7] = {
  {"C", "±", "%", "÷", "M+", "M-", "MC"},
  {"7", "8", "9", "×", "Tax", "Up", "Down"},
  {"4", "5", "6", "−", "Print", "WiFi", "BLE"},
  {"1", "2", "3", "+", "(", ")", "Back"},
  {"0", "00", ".", "=", "Subtotal", "Enter", "Mode"},
  {"F1", "F2", "F3", "F4", "F5", "F6", "F7"}
};

void flushDisplay(lv_disp_drv_t *disp, const lv_area_t *area, lv_color_t *colorMap) {
  const uint32_t width = area->x2 - area->x1 + 1;
  const uint32_t height = area->y2 - area->y1 + 1;
  gfx->draw16bitRGBBitmap(area->x1, area->y1, reinterpret_cast<uint16_t *>(colorMap), width, height);
  lv_disp_flush_ready(disp);
}

void initDisplay() {
  gfx->begin();
  gfx->fillScreen(BLACK);
  lv_init();
  const size_t pixels = LCD_WIDTH * 40;
  lvBuffer = static_cast<lv_color_t *>(heap_caps_malloc(pixels * sizeof(lv_color_t), MALLOC_CAP_SPIRAM));
  if (lvBuffer == nullptr) {
    Serial.println("Display buffer allocation failed");
    while (true) delay(1000);
  }
  lv_disp_draw_buf_init(&drawBuffer, lvBuffer, nullptr, pixels);
  lv_disp_drv_init(&displayDriver);
  displayDriver.hor_res = LCD_WIDTH;
  displayDriver.ver_res = LCD_HEIGHT;
  displayDriver.flush_cb = flushDisplay;
  displayDriver.draw_buf = &drawBuffer;
  lv_disp_drv_register(&displayDriver);

  lv_obj_t *title = lv_label_create(lv_scr_act());
  lv_label_set_text(title, "SMART DESKTOP CALCULATOR");
  lv_obj_set_style_text_color(title, lv_color_hex(0xFFFFFF), 0);
  lv_obj_set_style_text_font(title, &lv_font_montserrat_20, 0);
  lv_obj_align(title, LV_ALIGN_TOP_MID, 0, 28);
  lv_obj_t *total = lv_label_create(lv_scr_act());
  lv_label_set_text(total, "TOTAL  $123.45");
  lv_obj_set_style_text_color(total, lv_color_hex(0x44E3A3), 0);
  lv_obj_set_style_text_font(total, &lv_font_montserrat_28, 0);
  lv_obj_align(total, LV_ALIGN_TOP_MID, 0, 92);
  lv_obj_t *qr = lv_qrcode_create(lv_scr_act(), 210, lv_color_hex(0x111111), lv_color_white());
  lv_qrcode_update(qr, "CALC-RECEIPT:TOTAL=123.45", 25);
  lv_obj_align(qr, LV_ALIGN_TOP_MID, 0, 175);
  lv_obj_t *hint = lv_label_create(lv_scr_act());
  lv_label_set_text(hint, "Use keypad; press Print for a mock receipt");
  lv_obj_set_style_text_color(hint, lv_color_hex(0xB0B8C8), 0);
  lv_obj_align(hint, LV_ALIGN_TOP_MID, 0, 430);
}

void initKeypad() {
  if (!mcp.begin_I2C(MCP_ADDRESS, &Wire)) {
    Serial.println("MCP23017 not found at 0x20");
    return;
  }
  for (uint8_t row = 0; row < 6; ++row) {
    mcp.pinMode(row, OUTPUT);
    mcp.digitalWrite(row, HIGH);
  }
  for (uint8_t col = 0; col < 7; ++col) mcp.pinMode(8 + col, INPUT_PULLUP);
}

void printMockReceipt() {
  printer.wake();
  printer.setDefault();
  printer.justify('C');
  printer.boldOn();
  printer.println("SMART CALCULATOR");
  printer.boldOff();
  printer.println("------------------------------");
  printer.justify('L');
  printer.println("Mock transaction");
  printer.println("Items                 $123.45");
  printer.println("------------------------------");
  printer.boldOn();
  printer.println("TOTAL                 $123.45");
  printer.boldOff();
  printer.feed(3);
  printer.sleep();
}

void onKeyPressed(uint8_t row, uint8_t col) {
  const char *key = keyNames[row][col];
  Serial.printf("Key pressed: %s (row %u, column %u)\n", key, row, col);
  if (strcmp(key, "Print") == 0) printMockReceipt();
}

void scanKeypad() {
  const uint32_t now = millis();
  for (uint8_t row = 0; row < 6; ++row) {
    mcp.digitalWrite(row, LOW);
    delayMicroseconds(100);
    for (uint8_t col = 0; col < 7; ++col) {
      const bool pressed = (mcp.digitalRead(8 + col) == LOW);
      if (pressed != pendingKeys[row][col]) {
        pendingKeys[row][col] = pressed;
        changeTime[row][col] = now;
      }
      if ((now - changeTime[row][col] >= DEBOUNCE_MS) && stableKeys[row][col] != pendingKeys[row][col]) {
        stableKeys[row][col] = pendingKeys[row][col];
        if (stableKeys[row][col]) onKeyPressed(row, col);
      }
    }
    mcp.digitalWrite(row, HIGH);
  }
}

void readFuelGauge() {
  Wire.beginTransmission(MAX17049_ADDRESS);
  Wire.write(0x02);
  if (Wire.endTransmission(false) != 0 || Wire.requestFrom(MAX17049_ADDRESS, (uint8_t)2) != 2) return;
  const uint16_t raw = (Wire.read() << 8) | Wire.read();
  Serial.printf("Battery: %.2f V\n", raw * 78.125e-6f);
}

void initConnectivityStubs() {
  WiFi.mode(WIFI_STA);
  NimBLEDevice::init("SmartCalculator");
  NimBLEDevice::setPower(ESP_PWR_LVL_P3);
  Serial.println("Wi-Fi station and BLE stubs initialized");
}

void setup() {
  Serial.begin(115200);
  delay(300);
  Wire.begin(I2C_SDA, I2C_SCL);
  Wire.setClock(400000);
  printerSerial.begin(PRINTER_BAUD, SERIAL_8N1, PRINTER_RX, PRINTER_TX);
  initKeypad();
  initDisplay();
  initConnectivityStubs();
  readFuelGauge();
  lastTickMs = millis();
  Serial.println("Calculator hardware stack ready");
}

void loop() {
  const uint32_t now = millis();
  if (now - lastTickMs >= 5) {
    lv_tick_inc(now - lastTickMs);
    lastTickMs = now;
  }
  lv_timer_handler();
  scanKeypad();
  delay(2);
}