Six-Product Smart Refill Vending Machine

#include <Arduino.h>
#include <Wire.h>
#include <SPI.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <WiFiClientSecure.h>
#include <Adafruit_GFX.h>
#include <Adafruit_ILI9341.h>
#include <XPT2046_Touchscreen.h>
#include <HX711.h>
#include <OneWire.h>
#include <DallasTemperature.h>

constexpr int I2C_SDA = 8, I2C_SCL = 9;
constexpr int TFT_CS = 10, TFT_DC = 21, TFT_RST = 38, TOUCH_CS = 39;
constexpr int HX_WATER_DT = 1, HX_MILK_DT = 2, HX_OIL_DT = 3, HX_DET_DT = 4, HX_DISH_DT = 5, HX_HAND_DT = 6;
constexpr int HX_WATER_SCK = 18, HX_MILK_SCK = 40, HX_OIL_SCK = 41, HX_DET_SCK = 42, HX_DISH_SCK = 47, HX_HAND_SCK = 18; // shared electrical clock net with water HX711
constexpr int MILK_TEMP_PIN = 14, ESTOP_PIN = 15, LEAK_PIN = 16, FRIDGE_ENABLE_PIN = 17;
constexpr uint8_t PUMP_DRIVER = 0x20, VALVE_DRIVER = 0x21;
constexpr float MILK_MAX_C = 4.0f, LOW_STOCK_G = 1000.0f;
constexpr char WIFI_SSID[] = "";          // provision during commissioning
constexpr char WIFI_PASSWORD[] = "";
constexpr char BACKEND_URL[] = "";        // e.g. https://your-server.example
constexpr char DEVICE_TOKEN[] = "";       // short-lived device credential, never an M-Pesa secret

Adafruit_ILI9341 tft(TFT_CS, TFT_DC, TFT_RST);
XPT2046_Touchscreen touch(TOUCH_CS);
OneWire oneWire(MILK_TEMP_PIN);
DallasTemperature milkThermometer(&oneWire);
HX711 scales[6];
const int dtPins[6] = {HX_WATER_DT,HX_MILK_DT,HX_OIL_DT,HX_DET_DT,HX_DISH_DT,HX_HAND_DT};
const int sckPins[6] = {HX_WATER_SCK,HX_MILK_SCK,HX_OIL_SCK,HX_DET_SCK,HX_DISH_SCK,HX_HAND_SCK};
const char *names[6] = {"Water","Milk","Cooking oil","Detergent","Dishwash","Handwash"};
// Replace each factor during the calibration procedure; units are grams per displayed value.
float calibration[6] = {1,1,1,1,1,1};
float stockG[6] = {0,0,0,0,0,0};
int selectedProduct = 0;
int selectedQtyMl = 500;
float milkC = NAN;
bool dispensing = false;
uint8_t pumpBits = 0, valveBits = 0;
uint32_t lastUiMs = 0, lastSensorMs = 0;

void mcpWrite(uint8_t address, uint8_t reg, uint8_t value) {
  Wire.beginTransmission(address); Wire.write(reg); Wire.write(value); Wire.endTransmission();
}
void setOutputs(uint8_t &bits, uint8_t address, uint8_t newBits) {
  bits = newBits; mcpWrite(address, 0x00, 0x00); mcpWrite(address, 0x14, bits);
}
void allOff() { setOutputs(pumpBits, PUMP_DRIVER, 0); setOutputs(valveBits, VALVE_DRIVER, 0); dispensing = false; }
bool emergencyActive() { return digitalRead(ESTOP_PIN) == HIGH; } // NC contact opens when pressed
bool leakActive() { return digitalRead(LEAK_PIN) == LOW; }       // dry contact closes when wet
bool milkSafe() { return !isnan(milkC) && milkC >= 0.0f && milkC <= MILK_MAX_C; }
bool safeToDispense(int product) {
  return !emergencyActive() && !leakActive() && (product != 1 || milkSafe()) && stockG[product] > LOW_STOCK_G;
}

void drawUi() {
  tft.fillScreen(ILI9341_BLACK);
  tft.setTextSize(2); tft.setTextColor(ILI9341_WHITE); tft.setCursor(8, 6); tft.print("Household Refill");
  tft.setTextSize(1); tft.setCursor(8, 28); tft.print("Milk: "); tft.print(milkC, 1); tft.print(" C  ");
  if (emergencyActive()) tft.setTextColor(ILI9341_RED); else if (leakActive()) tft.setTextColor(ILI9341_RED); else tft.setTextColor(ILI9341_GREEN);
  if (emergencyActive()) tft.print("EMERGENCY STOP"); else if (leakActive()) tft.print("LEAK LOCKOUT"); else tft.print("SAFE");
  for (int i=0;i<6;i++) {
    int y = 45 + i*28; uint16_t color = (i == selectedProduct) ? ILI9341_BLUE : ILI9341_DARKGREY;
    tft.fillRect(4,y,210,24,color); tft.setTextColor(ILI9341_WHITE); tft.setCursor(8,y+7); tft.print(names[i]);
    tft.setCursor(135,y+7); tft.print(stockG[i]/1000.0f,1); tft.print("kg");
  }
  tft.fillRect(220,45,96,38,ILI9341_DARKCYAN); tft.setTextColor(ILI9341_WHITE); tft.setCursor(228,55); tft.print("-100 ml");
  tft.fillRect(220,90,96,38,ILI9341_DARKCYAN); tft.setCursor(228,100); tft.print("+100 ml");
  tft.fillRect(220,140,96,42,ILI9341_GREEN); tft.setTextColor(ILI9341_BLACK); tft.setCursor(232,151); tft.print("PAY");
  tft.setTextColor(ILI9341_WHITE); tft.setCursor(224,195); tft.print(selectedQtyMl); tft.print(" ml");
  tft.setCursor(224,215); tft.print("Backend verifies"); tft.setCursor(224,226); tft.print("M-Pesa payment");
}

bool backendPaymentConfirmed(int product, int quantityMl) {
  // The backend owns M-Pesa consumer key, secret, OAuth token and STK callback verification.
  // An empty URL deliberately denies dispensing until commissioning has configured a backend.
  if (strlen(BACKEND_URL) == 0 || WiFi.status() != WL_CONNECTED) return false;
  WiFiClientSecure client; client.setInsecure(); // commissioning only: replace with backend CA validation before production
  HTTPClient http;
  String url = String(BACKEND_URL) + "/api/v1/vend/authorize";
  if (!http.begin(client, url)) return false;
  http.addHeader("Content-Type", "application/json"); http.addHeader("Authorization", String("Bearer ") + DEVICE_TOKEN);
  String body = String("{\"product\":\"") + names[product] + "\",\"quantity_ml\":" + quantityMl + "}";
  int status = http.POST(body); String reply = http.getString(); http.end();
  return status == 200 && reply.indexOf("\"verified\":true") >= 0;
}

void dispenseByMass(int product, int quantityMl) {
  // For this prototype 1 ml is treated as 1 g. During product calibration, use density-correct target grams for oil/detergents.
  float targetG = (float)quantityMl;
  float startG = stockG[product];
  if (!safeToDispense(product)) return;
  setOutputs(valveBits, VALVE_DRIVER, valveBits | (1 << product));
  setOutputs(pumpBits, PUMP_DRIVER, pumpBits | (1 << product));
  dispensing = true; uint32_t started = millis();
  while (dispensing && millis() - started < 120000UL) {
    if (!safeToDispense(product)) break;
    if (scales[product].is_ready()) stockG[product] = scales[product].get_units(3);
    if (startG - stockG[product] >= targetG) break;
    delay(20);
  }
  allOff();
}

void readSensors() {
  milkThermometer.requestTemperatures(); milkC = milkThermometer.getTempCByIndex(0);
  for (int i=0;i<6;i++) if (scales[i].is_ready()) stockG[i] = scales[i].get_units(3);
  // Closed contact requests refrigeration only while milk is too warm; technician must connect only to approved appliance input.
  digitalWrite(FRIDGE_ENABLE_PIN, (!isnan(milkC) && milkC > 3.0f) ? HIGH : LOW);
  if (emergencyActive() || leakActive() || !milkSafe()) allOff();
}

void handleTouch() {
  if (!touch.touched()) return;
  TS_Point p = touch.getPoint();
  // Calibrate these raw ranges after fitting the physical display.
  int x = map(p.x, 200, 3800, 0, 320); int y = map(p.y, 200, 3800, 0, 240);
  if (x < 215 && y >= 45 && y < 213) selectedProduct = constrain((y - 45) / 28, 0, 5);
  else if (x >= 220 && y >= 45 && y < 83) selectedQtyMl = max(100, selectedQtyMl - 100);
  else if (x >= 220 && y >= 90 && y < 128) selectedQtyMl = min(5000, selectedQtyMl + 100);
  else if (x >= 220 && y >= 140 && y < 182) {
    if (backendPaymentConfirmed(selectedProduct, selectedQtyMl)) dispenseByMass(selectedProduct, selectedQtyMl);
  }
  delay(180); drawUi();
}

void setup() {
  pinMode(ESTOP_PIN, INPUT_PULLUP); pinMode(LEAK_PIN, INPUT_PULLUP); pinMode(FRIDGE_ENABLE_PIN, OUTPUT); digitalWrite(FRIDGE_ENABLE_PIN, LOW);
  Wire.begin(I2C_SDA, I2C_SCL); allOff();
  for (int i=0;i<6;i++) { scales[i].begin(dtPins[i], sckPins[i]); scales[i].set_scale(calibration[i]); scales[i].tare(); }
  milkThermometer.begin();
  SPI.begin(12,13,11,10); tft.begin(); tft.setRotation(1); touch.begin(); touch.setRotation(1);
  if (strlen(WIFI_SSID)) { WiFi.mode(WIFI_STA); WiFi.begin(WIFI_SSID, WIFI_PASSWORD); }
  readSensors(); drawUi();
}
void loop() {
  uint32_t now = millis();
  if (now - lastSensorMs >= 1000) { lastSensorMs = now; readSensors(); }
  if (now - lastUiMs >= 1000) { lastUiMs = now; drawUi(); }
  handleTouch();
  delay(10);
}