EE 476: Laboratory 3

One-octave keyboard.

You will construct a one-octave, single voice, square-wave output, keyboard synthesizer. The keyboard will produce the musical notes corresponding to:

        C4   262 Hz (middle C)
        D4   294
	E4   330
	F4   349
	G4   392
	A4   440
	B4   494
	C5   523
 

You will need to read a port (perhaps port0) to get key presses. Remember to use a 47k resistor pack with the switches as shown in Lab 2.

HSO.0 output can be programmed in a fashion similar to the code fragment given in Lab 2, but changing the variables "period" and "clear_t" for each different note. Unlike Lab 2, you will not be using timer2 as a time base in this lab.

HSO.0 can drive the earphone directly, but is somewhat loaded by the earphone. You can make it louder by using a 74xx driver or an op-amp.

Write a program which implements a one-octave keyboard synthesizer using eight switches connected to an input port and an earphone connected to HSO.0. HSO.0 should be programmed to produce a squarewave with a 50% dutycycle. The frequency of the notes should be accurate to better than 0.1%.

When you demonstrate the keyboard to a staff member, you will play a scale and a short melody of your choice. You may use the melody shown below. The keyboard needs to produce only one note at a time (single voice).

Notes: E  E  E  F  F   G  F  E  D  E  F   G  C  F  E   D   C   C
Play the hollow notes twice as long as the filled notes.

For extra credit do one of the following:

• construct a two voice synthesizer so that you can press two keys at once and hear two different notes. You may, of course, use external op-amps or other circuitry.
• Construct a playback feature to play a prestored melody.

Your written lab report should include:

• The scheme you used to detect the pushbutton state. (e.g. polling loop, interrupt)
• How you generated the freqencies and how you know they are accurate to 0.1%.
• Other design aspects of the assignment (e.g. did you use table lookup for the frequencies or did you hardcode them).
• An outline of how you would produce a second voice so that you could press two keys at once and hear two different notes.
• A heavily commented listing of your code.