Driver for a small, low power AM radio transmitter, to broadcast monophonic square wave tones over a short distance. This project was inspired by the book "Make: AVR Programming" by Elliot Williams. More...

#include <stdint.h>
#include "scale.h"

Enumerations
enum	frequency_khz_t { _500_KHZ = 500000 , _570_KHZ = 570000 , _670_KHZ = 670000 , _800_KHZ = 800000 , _1000_KHZ = 1000000 , _1333_KHZ = 1333000 }
	Enum to expose the predefined carrier frequency options. More...

enum	note_duration_t { SEMIBREVE , MINIM , CROTCHET , QUAVER , SEMIQUAVER , DEMISEMIQUAVER }
	Enum to expose the predefined duration options. More...

Functions
void	init_am_radio (frequency_khz_t carrier_freq)
	Initialises timer/counter for radio transmission at a specified carrier frequency. More...

void	am_radio_set_tempo (uint8_t tempo)
	Sets tempo for musical tones to be transmitted (in BPM). More...

void	am_radio_transmit_note (note_pitch_t pitch, note_duration_t note_length)
	Transmits a square wave, monophonic note for the specified duration. More...

void	am_radio_rest (note_duration_t rest_length)
	Waits a specified duration before playing the next note. More...

void	arpeggio_in_c_test (void)
	Test sequence, transmits an arpeggio scale in C major. More...

Detailed Description

Driver for a small, low power AM radio transmitter, to broadcast monophonic square wave tones over a short distance. This project was inspired by the book "Make: AVR Programming" by Elliot Williams.

Copyright: Copyright © 2022 by Jason Duffy.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Author: Jason Duffy

Date: 10th September 2022

Only tested with F_CPU = 8MHZ, but will build on this later to make it work with other CPU speeds.

Definition in file am_radio.h.

Enumeration Type Documentation

◆ frequency_khz_t

enum frequency_khz_t

Enum to expose the predefined carrier frequency options.

1000KHZ (1MHZ) is ideal, but may be taken in your locality so try another if there is too much interferance.

Definition at line 48 of file am_radio.h.

{   
    _500_KHZ = 500000,
    _570_KHZ = 570000,
    _670_KHZ = 670000,
    _800_KHZ = 800000,
    _1000_KHZ = 1000000,
    _1333_KHZ = 1333000,
}frequency_khz_t;

◆ note_duration_t

enum note_duration_t

Enum to expose the predefined duration options.

Definition at line 62 of file am_radio.h.

{
    SEMIBREVE,
    MINIM,
    CROTCHET,
    QUAVER,
    SEMIQUAVER,
    DEMISEMIQUAVER,
}note_duration_t;

Function Documentation

◆ init_am_radio()

void init_am_radio ( frequency_khz_t carrier_freq )

Initialises timer/counter for radio transmission at a specified carrier frequency.

Definition at line 47 of file am_radio.c.

{
    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();
}

◆ am_radio_set_tempo()

void am_radio_set_tempo ( uint8_t tempo )

Sets tempo for musical tones to be transmitted (in BPM).

Definition at line 80 of file am_radio.c.

{
    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
}

◆ am_radio_transmit_note()

void am_radio_transmit_note	(	note_pitch_t	pitch,
		note_duration_t	note_length
	)

Transmits a square wave, monophonic note for the specified duration.

Definition at line 94 of file am_radio.c.

{
    // 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);
}

◆ am_radio_rest()

void am_radio_rest ( note_duration_t rest_length )

Waits a specified duration before playing the next note.

Definition at line 119 of file am_radio.c.

{
    // Wait for specified time. 
    for (uint16_t count = 0; count < duration[rest_length]; ++count)
    {
        _delay_ms(1);
    }
}

◆ arpeggio_in_c_test()

void arpeggio_in_c_test ( void )

Test sequence, transmits an arpeggio scale in C major.

Definition at line 131 of file am_radio.c.

{
    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);
}

Enumerations

Functions