atmega-geiger/src/high_voltage.c

/**
 * High voltage source control logic
 */

#include "high_voltage.h"
#include "iopins.h"
#include "global_state.h"
#include <stdbool.h>
#include <avr/interrupt.h>
#include <util/atomic.h>

static volatile bool is_pwm_on = false;

// tube starting voltage is 350V
#define TURN_ON_VOLTAGE 355.0
#define TURN_OFF_VOLTAGE 380.0
#define MINIMAL_VOLTAGE 350.0

// sensing via resistive divider
#define VREF 1.1

// in kiloohms
#define R_UPPER 10000.0
#define R_LOWER 27.0

#define ADC_MAXVAL 1023

#define RDIV_FACTOR   (R_LOWER / (R_UPPER + R_LOWER))

/// ADC input voltage that's too low - PWM must start
#define VSEN_TURN_ON  (TURN_ON_VOLTAGE  * RDIV_FACTOR)
/// ADC input voltage that's too high - PWM must stop
#define VSEN_TURN_OFF (TURN_OFF_VOLTAGE * RDIV_FACTOR)
/// ADC input voltage that's lowest possible for the geiger tube to function
#define VSEN_MINIMAL  (MINIMAL_VOLTAGE  * RDIV_FACTOR)

// the above, but converted to ADC word
#define ADCVAL_TURN_ON  ((uint16_t) (ADC_MAXVAL * (VSEN_TURN_ON  / VREF)))
#define ADCVAL_TURN_OFF ((uint16_t) (ADC_MAXVAL * (VSEN_TURN_OFF / VREF)))
#define ADCVAL_MINIMAL  ((uint16_t) (ADC_MAXVAL * (VSEN_MINIMAL  / VREF)))

/// Channel used to measure VSEN
#define VSEN_ADC_CHANNEL 0


/// when capacitor was last fully charged
static volatile uint16_t ts_cap_charged = 0;

static void pwm_on()
{
    TCCR0A |= _BV(COM0B1);
    is_pwm_on = true;
}

static void pwm_off()
{
    TCCR0A &= ~_BV(COM0B1);
    is_pwm_on = false;
}


ISR(ADC_vect)
{
    // Service the boost converter
    uint16_t analog = ADCW;

    if (is_pwm_on) {
        if (analog >= ADCVAL_TURN_OFF) {
            pwm_off();
            ts_cap_charged = timestamp_100ms;
        } else {
            // If fail to reach target voltage in reasonable time,
            // show weak battery icon and stop trying.
            if ((timestamp_100ms - ts_cap_charged) > 10 && analog < ADCVAL_MINIMAL) {
                is_weak_battery = true;
            }
        }
    } else if (analog < ADCVAL_TURN_ON) {
        pwm_on();
    }
}


static void init_pwm_out()
{
    // Output is OC0A
    as_output(D5);

    // initialize the timer
    // Fast PWM mode, Output to OC0A

    // clock is 16MHz, presc /64, counting to 80 -> freq 3125Hz
    // Duty cycle = appx. 60%

    OCR0A = 80;
    OCR0B = 46;
    TCCR0A = _BV(WGM00) | _BV(WGM01);
    TCCR0B = _BV(CS01) | _BV(CS00) | _BV(WGM02);
}


static void init_adc()
{
    ADCSRA =
            // 128 prescaler -> 125 kHz
            _BV(ADPS2) | _BV(ADPS1) | _BV(ADPS0)
            // auto trigger
            | _BV(ADATE)
            // interrupt enable
            | _BV(ADIE);

    ADCSRB = 0; // free-running
    DIDR0 = ADC0D; // disable the digital input buffer on the pin

    ADMUX =
            // internal ref 1.1V
            _BV(REFS0) | _BV(REFS1)
            // select channel
            | VSEN_ADC_CHANNEL;

    sbi(ADCSRA, ADEN);  // Enable ADC
    sbi(ADCSRA, ADSC);  // Start
}


void init_high_voltage()
{
    init_pwm_out();
    init_adc();
}

void hv_disable()
{
    ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
        // if ADC is disabled, the IRQ never fires and it won't be turned on
        cbi(ADCSRA, ADEN);
        // Turn it off
        pwm_off();
    }
}