🌡️ Sensor Interfacing dengan Microcontroller

// Kalibrasi pH meter dengan 2 titik referensi
// Larutan buffer pH 4.0 dan pH 7.0

class PHSensor {
private:
    int _pin;
    float _acidVoltage;    // Voltage di pH 4.0
    float _neutralVoltage; // Voltage di pH 7.0
    float _slope;
    float _intercept;

public:
    PHSensor(int pin) {
        _pin = pin;
        _acidVoltage = 1.650;    // Default, harus dikalibrasi
        _neutralVoltage = 1.250;  // Default, harus dikalibrasi
        _calculateCoefficients();
    }

    // Kalibrasi dengan 2 titik
    void calibrateTwoPoint(float ph1, float voltage1,
                           float ph2, float voltage2) {
        // ph1 = 7.0 (neutral), voltage1 = voltage saat pH 7.0
        // ph2 = 4.0 (acid), voltage2 = voltage saat pH 4.0
        _neutralVoltage = voltage1;
        _acidVoltage = voltage2;
        _calculateCoefficients();
        Serial.printf("Kalibrasi: slope=%.4f, intercept=%.4f\n",
                      _slope, _intercept);
    }

    void _calculateCoefficients() {
        // Linear: pH = slope * voltage + intercept
        _slope = (7.0 - 4.0) / (_neutralVoltage - _acidVoltage);
        _intercept = 7.0 - _slope * _neutralVoltage;
    }

    float readVoltage() {
        long sum = 0;
        for (int i = 0; i < 40; i++) {
            sum += analogRead(_pin);
            delay(10);
        }
        float avg = sum / 40.0;
        return (avg / 4095.0) * 3.3;
    }

    float readPH() {
        float voltage = readVoltage();
        float ph = _slope * voltage + _intercept;
        return constrain(ph, 0.0, 14.0);
    }
};

// Setup kalibrasi
PHSensor phSensor(34);

void setup() {
    Serial.begin(115200);
    delay(3000);

    // Mode kalibrasi
    Serial.println("=== KALIBRASI pH METER ===");
    Serial.println("Celupkan ke larutan pH 7.0, lalu ketik 'ok'");
    while (!Serial.available()) {}
    float voltage7 = phSensor.readVoltage();
    Serial.printf("Voltage pH 7.0: %.4f V\n", voltage7);

    Serial.println("Celupkan ke larutan pH 4.0, lalu ketik 'ok'");
    while (!Serial.available()) {}
    float voltage4 = phSensor.readVoltage();
    Serial.printf("Voltage pH 4.0: %.4f V\n", voltage4);

    phSensor.calibrateTwoPoint(7.0, voltage7, 4.0, voltage4);
    Serial.println("Kalibrasi selesai!");
}

void loop() {
    float ph = phSensor.readPH();
    Serial.printf("pH: %.2f\n", ph);
    delay(2000);
}

// NTC Thermistor dengan Steinhart-Hart equation
// Lebih akurat dari linearisasi sederhana

#include <math.h>

#define THERMISTOR_PIN 34
#define R_FIXED 10000.0     // Resistor tetap 10KΩ
#define R_NTC_25 10000.0    // Resistansi NTC pada 25°C
#define B_COEFFICIENT 3950  // Beta coefficient dari datasheet

float readNTCTemperature() {
    // Baca ADC
    int raw = analogRead(THERMISTOR_PIN);

    // Hitung resistansi NTC
    // Voltage divider: Vout = Vcc * R_fixed / (R_ntc + R_fixed)
    float voltage = (raw / 4095.0) * 3.3;
    float r_ntc = R_FIXED * (3.3 / voltage - 1.0);

    // Steinhart-Hart (simplified with B coefficient)
    // 1/T = 1/T0 + (1/B) * ln(R/R0)
    float tempK = 1.0 / (
        (1.0 / 298.15) +                    // 1/T0 (T0=25°C=298.15K)
        (1.0 / B_COEFFICIENT) * log(r_ntc / R_NTC_25)
    );

    float tempC = tempK - 273.15;

    // Atau gunakan persamaan Steinhart-Hart penuh (3 titik kalibrasi):
    // 1/T = A + B*ln(R) + C*(ln(R))^3
    // Perlu mengukur resistansi pada 3 suhu berbeda

    return tempC;
}

void setup() {
    Serial.begin(115200);
}

void loop() {
    float suhu = readNTCTemperature();
    Serial.printf("Suhu: %.2f °C\n", suhu);
    delay(1000);
}