CSE466-03au Lab Assignment 5

This is a 3 part lab. In it, you will:

1. Add Envelope (amplitude) to your control of the piezoelectric transducer.
2. Parse MIDI-derived birdsongs.
3. Play the birdsongs through the piezoelectric transducer.

In this lab you will learn the following:

• how to program a timer pulse-width modulator output for pulse amplitude and frequency
• how to calculate frequencies and phase-increments of musical scales, based on the MIDI standard

Steps

Part 1

1. Sample code is provided as Birdie.c. Compile this file and load it. You need to connect your  piezoelectric transducer  directly to PD5 (pin 19) and to ground.
2. Listen to the output. Observe the PD5 output with your oscilloscope.  Determine the PWM frequency. Based on the data sheet, calculate the exact sample rate with a clock frequency of 7.3728MHz., and the PWM mode used.
3. Calculate an RC filter with a -3dB point at approximately 0.25 of the PWM frequency (using the nearest values you can find) and connect it to PD5. Connect your oscilloscope probes to the PD5 pin and to the output of the RC filter. Describe what you see for turn-in, and show your calculations.
4. Modify the program to read an ADSR envelope table to control amplitude, using timer/counter 2 for control. See comments in Birdie.c.  

5. Demonstrate your program to a TA, who will check your code for timer 2 usage.

End of part 1

Part 2

1. Add a phase accumulator to your code, that addresses a two-sample table, consisting of “upper” and “lower”. The waveshape is a square wave.
2. The table is accessed by the MSB of your phase accumulator, which is incremented each sample by a phase increment value. b’0 = upper, b’1 = lower.
3. phase_index = modL(previous_phase + increment)
4. increment = (TableLength x DesiredFrequency)/ SampleRate
5. Your program should output four notes,  corresponding to A5, 880Hz, A6, 1760Hz, A7, 3520Hz, and A8, 7040Hz. A push button should step between notes, with another button starting and stopping the pitch. Amplitude should be 127.
6. Observe the output with your oscilloscope. Your low-pass filter may need to be adjusted for smooth performance. We should be able to measure the frequencies.
7. Demonstrate your pitch generator to a TA.

End of part 2

Part 3

1. Birdsong MIDI files for listening are in Birdsongs.zip; the text versions are in birdsmidtxt.zip for adapting to your program.

Here is a sample birdsong in text format:

// \Birdsongs\btwa.mid

mthd

  version 0 // single multichanneltrack

  // 1 track

  unit 100 // is 1/4

end mthd

mtrk(1)  // track 1

 /* U0 */  /* 0ms */   trackname "BTWA.MID"

 /* U0 */  /* 0ms */   text "created from WAV file by WAV2MID (C) Tanager Productions"

 /* U0 */  /* 0ms */   beats 120.00000 /* 500000 microsec/beat */

 /* U0 */  /* 0ms */   program ChoirPd

  96; /* U96 */  /* 480ms */ +f#7 $64;

  6; /* U102 */  /* 510ms */ -f#7 $00;

  27; /* U129 */  /* 645ms */ +f#7 $64;

  17; /* U146 */  /* 730ms */ -f#7 $00;

  24; /* U170 */  /* 850ms */ +f#7 $64;

  31; /* U201 */  /* 1005ms */ -f#7 $00;

  38; /* U239 */  /* 1195ms */ +f#7 $64;

  27; /* U266 */  /* 1330ms */ -f#7 $00;

 /* U266 */  /* 1330ms */   +f7 $64;

  4; /* U270 */  /* 1350ms */ -f7 $00;

 /* U270 */  /* 1350ms */   +d#7 $64;

  10; /* U280 */  /* 1400ms */ -d#7 $00;

 /* U280 */  /* 1400ms */   +d7 $64;

  17; /* U297 */  /* 1485ms */ -d7 $00;

 /* U297 */  /* 1485ms */   +d#7 $64;

  7; /* U304 */  /* 1520ms */ -d#7 $00;

 /* U304 */  /* 1520ms */   +f#7 $64;

  10; /* U314 */  /* 1570ms */ -f#7 $00;

 /* U314 */  /* 1570ms */   +g7 $64;

  4; /* U318 */  /* 1590ms */ -g7 $00;

 /* U318 */  /* 1590ms */   +f#7 $64;

  3; /* U321 */  /* 1605ms */ -f#7 $00;

 /* U321 */  /* 1605ms */   +g7 $64;

  4; /* U325 */  /* 1625ms */ -g7 $00;

 /* U325 */  /* 1625ms */   -c-1 $00;

 /* U325 */  /* 1625ms */

end mtrk

MIDI unit position and time position are shown in comments before each command:

/* U7765 */ /* 34085ms */

Comments are inside /* ... */ or start with // till end of line.

Pauses are shown before commands either in MIDI units ( 47; )or musical notation ( 536/4; ).

MIDI notes consists of pairs of commands: Note on is displayed as + and Note off is displayed as -

MIDI channel are displayed in mtrk(channel number) or as [channel number] inside a track before a command.

Values are shown decimal (0-127) or hexadecimal ($00 - $7F).

Hint—use the lines with – notes (note off events); the first value is the number of milliseconds of duration of the event, in 5 millisecond steps.

Standard MIDI file format is here.

2. Construct a new program based on Birdie.c, with the following characteristics:

· Timer2 controls the tempo and the length of each tone.

· Timer1 with PWM gives the frequency.

· The program plays the 16 birdsongs, selected by a button

· One button selects which birdsong (displayed 1-16)

· One button is start/stop

· The output is a pulse wave to the transducer, amplitude controlled by an ADSR envelope, scaled to the note

3. Read the comments in Birdie.c for hints.
4. Demonstrate your birdie to a TA.
5. Turn in a hard copy of your code.

Deliverables

For all files turned in, the comments at the top of the file should contain:

• Both partners' full name, login and student number.
• The lab number and the part of the lab (e.g. Lab 4, part2 for the sine-wave generator).
• Any extra calculations or data that we've asked for.

Part 1:

1. Demonstrate your program and circuit to a TA. You can either do this during this lab, or during the first 1/2 hour of the next lab.
2. Turn in the requested calculations and descriptions.

Part 2:

1. Demonstrate your pitch generator to a TA. We should be able to measure the frequencies. You can either do this during this lab, or during the first 1/2 hour of the next lab.

Part 3:

1. Demonstrate your birdie to a TA. You can either do this during this lab, or during the first 1/2 hour of the next lab.
2. Turn in hardcopy of your commented C code.

End