am_radio.c

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/******************************************************************************
 @copyright Copyright © 2022 by Jason Duffy.
 
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/**
 * @file am_radio.c
 * @ingroup am_radio
 * @author Jason Duffy
 * @date 10th September 2022
 * @brief Driver for a small, low power AM radio transmitter, to broadcast
 * monophonic square wave tones over a short distance. 
 */
 
#include <avr/power.h>
#include <avr/interrupt.h>
#include <util/delay.h>
 
#include "am_radio.h"
#include "pin_defines.h"
 
 
// Set default values based on 120BPM tempo. 
static uint16_t duration[6] = {2000,1000,500,250,125,62};
 
 
/*
 * Initialises timer/counter for radio transmission at a specified carrier frequency.
 */
void init_am_radio(frequency_khz_t carrier_freq)
{
    cli();
    // ----------------- TIMER 0 setup ------------------ //
    TCCR0A |= (1 << WGM01); // Timer 0 in CTC mode. 
    TCCR0A |= (1 << COM0B0); // Toggle OC0B on compare match.
    TCCR0B |= (1 << CS00); // Prescaler of 1.
 
    // F_CPU / (2 * 1 * (1 + 3)) = Carrier_freq
    // 8,000,000 / (2 * 1 * (1 + 3)) = 1,000,000
    uint8_t count_value = (((F_CPU / carrier_freq) / 2) - 1); // calculate count value. 
    OCR0A = count_value; // Set the carrier frequency.
 
    // ----------------- TIMER 1 setup ------------------ //
 
    // TODO: Make this setup dependant on F_CPU and carrier_freq_khz.
 
    TCCR1B |= (1 << WGM12); // Timer 1 in CTC mode.
    TCCR1B |= (1 << CS11); // Prescaler of 8.
    TIMSK1 |= (1 << OCIE1A); // Enable output compare match interrupt.
    sei();
}
 
 
ISR(TIMER1_COMPA_vect)
{
    ANTENNA_DDR ^= (1 << ANTENNA); // Toggle carrier on and off.
}
 
 
/*
 * Sets tempo for musical tones to be transmitted (in BPM).
 */
void am_radio_set_tempo(uint8_t bpm)
{
    duration[SEMIBREVE] = (60000 / bpm) * 4;
    duration[MINIM] = (duration[SEMIBREVE] >> 1); // Div by 2
    duration[CROTCHET] = (duration[MINIM] >> 1); // Div by 2
    duration[QUAVER] = (duration[CROTCHET] >> 1); // Div by 2
    duration[SEMIQUAVER] = (duration[QUAVER] >> 1); // Div by 2
    duration[DEMISEMIQUAVER] = (duration[SEMIQUAVER] >> 1); // Div by 2
}
 
 
/*
 * Transmits a square wave, monophonic note for the specified duration.
 */
void am_radio_transmit_note(note_pitch_t pitch, note_duration_t note_length)
{
    // Set pitch. 
    OCR1A = pitch;
 
    // Enable interrupts. 
    sei();
 
    // Wait for specified time. 
    for (uint16_t count = 0; count < duration[note_length]; ++count)
    {
        _delay_ms(1);
    }
 
    // Disable interrupts. 
    cli();
 
    // Back to full carrier freq. 
    ANTENNA_DDR |= (1 << ANTENNA);
}
 
 
/*
 * Waits a specified duration before playing the next note. 
 */
void am_radio_rest(note_duration_t rest_length)
{
    // Wait for specified time. 
    for (uint16_t count = 0; count < duration[rest_length]; ++count)
    {
        _delay_ms(1);
    }
}
 
 
/*
 * Test sequence, transmits an arpeggio scale in C major. 
 */void arpeggio_in_c_test(void)
{
    am_radio_transmit_note(C2, CROTCHET);
    am_radio_rest(QUAVER);
    am_radio_transmit_note(E2, CROTCHET);
    am_radio_rest(QUAVER);
    am_radio_transmit_note(G2, CROTCHET);
    am_radio_rest(QUAVER);
    am_radio_transmit_note(C3, CROTCHET);
    am_radio_rest(QUAVER);
    am_radio_transmit_note(G2, CROTCHET);
    am_radio_rest(QUAVER);
    am_radio_transmit_note(E2, CROTCHET);
    am_radio_rest(QUAVER);
}
 
 
 
/*** end of file ***/