Tutorial 2 Timer and Music Examples

Task 1. Complete the music note spreadsheet and play them with two buttons. (30 points)

The goal of this tutorial is to output a sound when a button is pressed. The strategy is when the button is pressed (slow compared to a computer system), the timer will count, overflow, and reset for many times, each time it overflows (as a flag), the digital I/O is toggled. The counts in a timer can be modified so the time it takes to overflow a timer is customizeable. In this case, it creates a certain frequency at the I/O which becomes a certain tone for a music note.

Let's calculate the TIMER1 counts first.

Duplicate the following tabel into a excel spreadsheet.

Index	Note	Freq (Hz) 3 sig figs	Period (ms) 3 sig figs	Half period (ms) 3 sig figs	TMR1 cnts
0	A4	440
1	A#4	466
2	B4	494
3	C4	523
4	C#4	554
5	D4	587
6	D#4	622
7	E4	659
8	F4	698
9	F#4	740
10	G4	784
11	G#4	831
12	A5	880
13	A#5	932
14	B5	987
15	C5	1046
16	C#5	1108
17	D5	1174
18	D#5	1244
19	E5	1318
20	F5	1396
21	F#5	1479
22	G5	1567
23	G#5	1660
24	A6	1759
25	A#6	1864
26	B6	1975
27	C6	2092
28	C#6	2216
29	D6	2348
30	D#6	2488
31	Ultrasonic	31,000

Music scale has the following properties:





This is how Column C were calculated.





Apply the function shown in the following snapshot. It is basically 1.059453^1, and rounded to 0 number of digits after the decimal points (intergers only).



For column D, find the periods in mlli seconds.



In column E, find the half peiod in milli seconds.



Timers 0 and 2 are 8-bit timers; Timers 1, 3, 4, and 5 are 16-bit timers.
Here is the example code for this tutorial.

Given that the prescaler is set at 1:1 which will be counted 16x10^6 per second (16 MHz). The TIMER1 counts should be calculated as follows:

For example 3 ms is the half period, counts should be 3*16000000/1000, it oscillates 16M times a second to counts to 3/1000 second, it should count up to 16M * 3/1000
Timer1 is 16 bits so if it counts from 0, it will count for 2^16 times until overflow occurs. When the counter is up, the speaker pin toggles once.
In column F, find the counts needed within this half period using this timer.

Here are the relevant registers for this example.









Here is the demo video:



Task 2. Play a longer song automatically (70 points)

From the kid songs website you can select the song you prefer. 
The goal of this task is to play longer music notes automatically. Since no one is going to press a button to play a note so certain time intervals must be defined.

Program requirements:

• Have a 32nd rest between notes.
• 0.5 second for note durations.
• Use Timer 3 with a 1:1 prescaler to generate the note frequencies
• Use Timer 1 with a 1:256 prescaler to generate the note durations,
• The array storing the notes of the song should have the index of the scale of each note. For example, my code which plays Twinkle Twinkle Little Star, has the following declaration:

uint16_t scale[6] = {9088, 8112, 7232, 12144, 10816, 9632};  // Frequencies as timer counts
uint8_t notes[14] = {E4, E4, B5, B5, C_5, C_5, B5, A5, A5, G_4, G_4, F_4, F_4, E4};//The song

C_5 means C#5 in the spreadsheet.

The symbols in the notes array "B5", "A5", etc. are #defined to index in the scale array which contains the half period of that note. For example, since the half period of a E4 note is 12144 timer 3 counts (which is index 4 in the scale array defined above), my code contains the following #define at the top of the program:
            #define E4 3

The 1:256 prescaler will slow down the 16MHz clock by 256 times for TIMER1. Which gives you 16000000/256 = 62500 Hz. 62500 counts/s * 0.5 seconds gives you 31250 counts.

Play the first two lines of the song Twinkle Twinkle Little Star



The demo video: