Cutdown_ADC.cpp

/* Author: Alex St. Clair
 * Filename: Cutdown_ADC.h
 * Created: 12-17-18
 * 
 * Defines a driver to use the SAMD21 ADC through the Arduino IDE
 */

#include "Cutdown_ADC.h"
#include "Cutdown_Logger.h"
#include "Cutdown_Configure.h"

// returns the temperature in celsius given the MCP9700A thermistor voltage
float calculate_temperature(float voltage)
{
    return (voltage - THERM_OFFSET) * THERM_COEFFICIENT;
}

// returns the temperature in fahrenheit given the MCP9700A thermistor voltage
float calculate_fahrenheit(float voltage)
{
    return ((voltage - THERM_OFFSET) * THERM_COEFFICIENT) * (1.8f) + 32;
}

// returns true if the squib is present and not fired (or shorted), false if not
bool check_squib(float voltage)
{
    return (voltage < SQUIB_THRESHOLD);
}

// ADC_Channel methods ------------------------------------------
ADC_Channel::ADC_Channel(float last, float divide, uint8_t pin)
{
    last_voltage = last;
    divider = divide;
    pin_number = pin;
}

float ADC_Channel::read(void)
{
    last_voltage = (float) analogRead(pin_number) / ADC_MAX * REFERENCE_VOLTAGE / divider;

    return last_voltage;
}

float ADC_Channel::check(void)
{
    return last_voltage;
}

// Cutdown_ADC methods ------------------------------------------
Cutdown_ADC::Cutdown_ADC() :
    thermistor  (0.0f,  THERM_DIVIDE, THERMISTOR),
    squib_pri   (0.0f,  SQUIB_DIVIDE, VMON_SQUIB_PRI),
    squib_bck   (0.0f,  SQUIB_DIVIDE, VMON_SQUIB_BCK),
    v_batt_pri  (12.0f, VBATT_DIVIDE, VMON_BATT_PRI),  // needs to start above low-battery threshold
    v_batt_bck  (12.0f, VBATT_DIVIDE, VMON_BATT_BCK)   // needs to start above low-battery threshold
{ }

void Cutdown_ADC::init(void)
{
    analogReference(AR_INTERNAL2V23); // internal 2.23V reference
    analogReadResolution(12); // 12-bit resolution
    last_temps[0] = cutdown_config.temp_set_point;
    last_temps[1] = cutdown_config.temp_set_point;
    last_temps[2] = cutdown_config.temp_set_point;
    last_temps[3] = cutdown_config.temp_set_point;
}

// TODO: add hysteresis!
void Cutdown_ADC::thermal_control(void)
{
    static bool heating = false;
    static uint8_t temp_num = 0;

    // get a new reading
    float temp = calculate_temperature(thermistor.read());
    cutdown_log(LOG_DEBUG, "temp ", temp);
    cutdown_log(LOG_DEBUG, "volt ", thermistor.check());

    // store the new temp in the circular bufferred array
    last_temps[temp_num] = temp;
    temp_num = (temp_num + 1) % 4;

    // update the running average
    float avg_temp = 0.0f;
    for (int i = 0; i < 4; i++) avg_temp += last_temps[i];
    avg_temp /= 4;

    // check if the heater state should change
    if (cutdown_config.temp_set_point > avg_temp && !heating) {
        digitalWrite(HEATER_GATE, HIGH);
        cutdown_log(LOG_DEBUG, "Heater on");
        heating = true;
    } else if (cutdown_config.temp_set_point < avg_temp && heating) {
        digitalWrite(HEATER_GATE, LOW);
        cutdown_log(LOG_DEBUG, "Heater off");
        heating = false;
    }
}