atmega-geiger/src/main.c

#include "twi.h"
#include "ssd1306.h"
#include "sevenseg.h"
#include "adc.h"
#include "iopins.h"
#include <avr/interrupt.h>
#include <util/atomic.h>

static void show_loading_icon();
static void show_empty_battery_icon();
static void shutdown_due_to_weak_battery();
static void show_current_radiation();

static void second_callback_irq();

// 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

static struct SevenSeg sseg = {
    .x0 = 0,
    .y0 = 0,
    .charwidth = 17,
    .thick = 3,
    //.charwidth = 16,
    //.thick = 1,
    .spacing = 4,
};

static volatile bool is_pwm_on = false;
static volatile bool req_update_display = false;
static volatile bool is_weak_battery = false;

#define MEAS_BIN_COUNT 120
typedef uint8_t meas_bin_t;
#define MEAS_MAX_COUNT 255

/// measurements in the last X seconds
static volatile meas_bin_t measurements[MEAS_BIN_COUNT];
/// Currently active measurement bin, increments once per second
static volatile uint8_t meas_bin = 0;

/// timestamp counted in units of 100ms
static volatile uint16_t timestamp_100ms = 0;
/// sub-second counter, counts 0-9 then overflows
static volatile uint16_t subsec_counter = 0;

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

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

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

// geiger tube pin change interrupt
ISR(INT0_vect)
{
    if (measurements[meas_bin] < MEAS_MAX_COUNT) {
        measurements[meas_bin]++;
    }
    req_update_display = true;
}

// 1 second counter
ISR(TIMER1_COMPA_vect)
{
    timestamp_100ms++;

    subsec_counter++;
    if (subsec_counter == 10) {
        subsec_counter = 0;
        second_callback_irq();
    }
}

static void second_callback_irq()
{
    meas_bin++;
    if (meas_bin >= MEAS_BIN_COUNT) {
        meas_bin = 0;
    }
    measurements[meas_bin] = 0;
    req_update_display = true;
}

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_pcisr() {
    as_input(D2);

    // using INT0 - arduino pin D2
    EICRA = _BV(ISC01) | _BV(ISC00); // rising edge
    EIMSK = _BV(INT0);
}

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_second_base() {
    // CTC & presc=256
   TCCR1B = (1 << WGM12) | (1 << CS12);
   TIMSK1 = (1 << OCIE1A); // Enable CTC interrupt
   OCR1A   = 6250; // 100ms
}

static void vsen_adc_init() {
    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 __attribute__((noreturn)) main() {
    // clear the measurement buffer
    memset((void*) measurements, 0, sizeof(measurements));

    TWI_Init();


    init_second_base();

    init_pwm_out();

    ssd1306_128x32_i2c_init();
    ssd1306_clearScreen();

    // TODO use ADC interrupt

    init_pcisr();

    // TODO show loading icon (can't show anything useful at least until the first tick arrives)
    show_loading_icon();

    // --- let's go ---
    sei();

    vsen_adc_init();

    for (;;) {
        _delay_ms(100);

        // check if redraw is needed
        bool update_display = false;
        ATOMIC_BLOCK(ATOMIC_FORCEON) {
            update_display = req_update_display;
            req_update_display = false;
        }

        if (update_display) {
            show_current_radiation();
        }

        if (is_weak_battery) {
            shutdown_due_to_weak_battery();
        }
    }
}

void show_current_radiation()
{
    // TODO
    sseg_number(&sseg, timestamp_100ms, 5, 0);
}

void __attribute__((noreturn)) shutdown_due_to_weak_battery()
{
    pwm_off();

    show_empty_battery_icon();

    cli();

    // try to preserve power; but the display will still drain the battery.
    // we should probably shut it off too.

    for(;;) {
        sleep_enable();
        sleep_cpu();
    }
}

void show_empty_battery_icon()
{
    // TODO
    sseg_number(&sseg, 9999, 5, 0);
}

void show_loading_icon()
{
    // TODO
    sseg_number(&sseg, 0, 5, 0);
}