/*
 * Electrical Conduction Tester  
 *
 * Created: 5/30/2022 5:35:20 PM
 *  Author: www.henteko.org
 */ 

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include <stdio.h>

#define cbi(addr, bit)     addr &= ~(1<<bit)
#define sbi(addr, bit)     addr |=  (1<<bit)
#define ADC_ENABLE	(_BV(ADEN)|_BV(ADIF)|0b111)
#define ADC_START	(ADC_ENABLE|_BV(ADSC))
unsigned int cnt;

// millisecond delay
void delay_ms(unsigned int t) {
	while(t--)
		_delay_ms(1);
}

// adc routine
unsigned int get_adc(unsigned char ch) {
	ADMUX = ch;			// Vref = Vcc
	ADCSRA = ADC_START;
	loop_until_bit_is_set(ADCSRA, ADIF);

	return ADCW;
}

// interrupt routine
ISR(TIMER1_OVF_vect) {
	TCNT1 = 12;
	cnt++;	// 1.024ms * (256 - 12) = 0.249856sec also 0.25sec
}

// power down
void powerdown() {
	cbi(PORTB, PB3);		// power down
}

int main(void) {
	unsigned int ad1, ad2;
	unsigned int pdown, poff;
	
	DDRB = _BV(PB0)|_BV(PB1)|_BV(PB3);	// PB0 led. PB1 sound(PWM). PB3 power on keep.

	TCCR0A = _BV(WGM01)|_BV(WGM00)|_BV(COM0B1);	// 8bit high speed PWM
	OCR0A = 160;	// 780Hz
	OCR0B = 80;		// duty 50%

	TCCR1 = 11;				// Timer1 prescaler 1/1024 .. 1.024ms
	TIMSK = _BV(TOIE1);		// Timer1 Overflow Interrupt Enable
	
	ADCSRA = ADC_ENABLE;
	
	cnt = 0;
	pdown = poff = 0;
	sbi(PORTB, PB3);		// power on hold
	sbi(PORTB, PB0);		// power indicator led on
	sei();
	
	while (1) {
		
		if(cnt > 1200)			// auto power off about 5 minute (0.25 * 1200)
			powerdown();

		ad1 = get_adc(1);		// sense battery
		if(ad1 < 620)			// under 2.0V
			poff++;
		else
			poff = 0;

		if(ad1 < 682)			// under 2.2V
			pdown++;
		else
			pdown = 0;
		
		if(poff > 20)			// powerdown
			powerdown();

		if(pdown > 20) {		// brink indicator by battery low 
			if(cnt % 2)
				sbi(PORTB, PB0);
			else
				cbi(PORTB, PB0);
		} else
				sbi(PORTB, PB0);

		ad2 = (get_adc(2) + get_adc(2) + get_adc(2)) / 3;		// sense conduction
		if(ad2 < 192) {
			TCCR0B = _BV(WGM02)|2;		// pwm on. highspeed PWM. prescaler 1/8
			cnt = 0;
		} else {
			TCCR0B = 0;					// pwm off.
		}
	}
}