73 lines
1.6 KiB
C
73 lines
1.6 KiB
C
/*
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* Use the timer to produce a sound in a speaker.
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*
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* Formular for the frequency:
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* (F_CPU/wanted_frequency*2*Prescaler)+1
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*
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* Cut off the decimal part and see which is
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* closer to the wanted frequency.
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*
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* Task: Sum at start with 440 Hz, when a button is pushed, sum at 264 Hz. The
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* other button reverses.
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*/
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#define F_CPU 16000000UL
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#define __AVR_ATmega328P__
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#include <avr/interrupt.h>
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#include <avr/io.h>
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#include <util/delay.h>
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#define SOUND_A 17
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#define SOUND_C 30
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#define MINUTE 60 * 1000
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const int TIME = 45 * MINUTE;
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int state = 0;
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// Timer0 interrupt
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ISR(TIMER0_COMPA_vect) {
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PORTB ^= (1 << PORTB5); // toggle the speaker
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}
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// code for INT0
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ISR(INT0_vect) {
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OCR0A = SOUND_A; // max value for timer
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}
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// code for INT1
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ISR(INT1_vect) {
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OCR0A = SOUND_C; // max value for timer
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}
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int main(void) {
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DDRB = 0xff; // write to B
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DDRD = 0; // read from D
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PORTD |= (1 << PORTD2) | (1 << PORTD3); // pull up D2 and D3
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PORTB = 0; // pull down PORT B
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// enable external interruprs
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EIMSK |= (1 << INT0);
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EIMSK |= (1 << INT1);
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// trigger when anything changes
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EICRA |= (1 << ISC00); // for INT0
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EICRA |= (1 << ISC10); // for INT1
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// Timer 0
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// Mode: Overflow, Interrupt
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// Prescaler: /1024
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// max: dynamic depending on pushed button
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TCCR0A |= (1 << WGM01); // CTC Mode
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OCR0A = SOUND_C; // max value for timer
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TIMSK0 |= (1 << OCIE0A); // enable interrupt ISR_COMPA_vect
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sei(); // magic interrupt macro
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TCCR0B |= (1 << CS02) | (1 << CS00); // enable with prescaler 1024
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while (1) {
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// do nothing
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}
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}
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