/*
 * MotionActivatedLightSwitch.c
 *
 * Created: 1/1/2013 3:57:11 PM
 *  Author: grist.carrigafoyl
 *  Target: ATtiny85

 Activate a pin when motion is detected via a PIR sensor on another pin. Checks
ambient light level via a photoresistor on an analog input.

Didn't implement TIMER_POT in this version.
 */

#define F_CPU           8000000UL  //  8Mhz
#define ADMUX_BITS      0b0000     // All default (VCC ref, ADLAR unset)
#define TIMER_POT       0b0001     // ADC1 PB2 (pin7)
#define PHOTORESISTOR       0b0011     // ADC3 PB3 (pin2)
#define PIR_PIN         PB0    // PCINT0 (pin5)
#define SWITCH_PIN      PB1    // pin6

// The light level below which the switch will trigger.
#define LOW_LIGHT_LEVEL     300 // Based on experimentation.

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

// Prototypes
int main(void);
int read_adc(char pin);

int main(void)
{
    char pir_state;
    int curr_light_level;

    // ADC settings. Check with data sheet that this is what you want
    ADCSRA |= _BV(ADEN) | // Enable ADC
        (_BV(ADPS1)) | // set pre-scaler to clock/128
        (_BV(ADPS0)) | // 8MHz/128 = 62.5Khz (aiming for 50 - 200)
        (_BV(ADPS2));  // so this is good.

    DDRB = _BV(SWITCH_PIN); // All input except the switch pin
    PORTB = _BV(PIR_PIN);  // Internal pullup for the PIR pin

    // How long the light stays on for. Simple constant for now
    int delay_time = 5000;
    for (;;) {
        pir_state = ~PINB & _BV(PIR_PIN);
        if (pir_state != 0) {  // Movement detected
            curr_light_level = read_adc(PHOTORESISTOR);
            if (curr_light_level < LOW_LIGHT_LEVEL) {
                PORTB |= _BV(SWITCH_PIN);  // On
                _delay_ms(delay_time);
            }
        }
        PORTB &= ~_BV(SWITCH_PIN); // Off
    }
    return 0; // Never going to happen
}

int read_adc(char pin)
{ // Read the analog value from the ADC input pin.
    // Code based on samples from http://avrbasiccode.wikispaces.com/
    int ret_val;

    // Assumes ADCSRA enabled and prescalars are set already
    // Set the input channel and other ADMUX bits
    ADMUX = (ADMUX_BITS << 4) | pin;

    // Discard the first reading in case it had its settings changed mid-conversion
    ADCSRA |= _BV(ADSC); // start a single conversion
    while (ADCSRA & _BV(ADSC)); // wait until conversion is done

    ADCSRA |= _BV(ADSC); // start a single conversion
    while (ADCSRA & _BV(ADSC)); // wait until conversion is done

    ret_val = ADCL; // Get ADCL first for 10bit and combine with ADCH
    return((ADCH << 8) | ret_val);
}