What is a Microcontroller (Paralax, v2.2, student guide, 2004)

Chapter #8: Frequency and Sound · Page 243

Depending on the octave, we want to divide noteFreq by either 1, 2, 4, or 8. That means that the goal is really to divide by 20 = 1, 21 = 2, 22 = 4, or 23 = 8. The statement below takes the value of noteOctave, which could be a value between 5 and 8, and subtracts that value from 8. If noteOctave was 8, now it’s 0. If noteOctave was 7, now it’s 1. If noteOctave was 6, now it’s 2, and if noteOctave was 5, now it’s 3.

noteOctave = 8 - noteOctave

Now, noteOctave is a value that can be used as an exponent of 2, but how do you raise 2 to a power in PBASIC? One answer is to use the DCD operator. DCD 0 is 1, DCD 1 is 2, DCD 2 is 4, and DCD 3 is 8. Dividing noteFreq by DCD noteOctave means you are dividing by 1, 2, 4, or 8, which divides noteFreq down by the correct value. The end result is that noteFreq is set to the correct octave. You will use the Debug Terminal in the Your Turn section to take a closer look at how this works.

noteFreq = noteFreq / (DCD noteOctave)

How am I supposed to know to use the DCD operator? Keep learning and practicing. Every time you see a new command, operator, or any other keyword used in an example, look it up in the BASIC Stamp manual. Read about it, and try using it in a program of your own design. Get in the habit of periodically reading the BASIC Stamp Manual and trying the short example programs. That’s the best way to get familiar with the various commands and operators and how they work. By doing these things, you will develop a habit of always adding to the list of programming tools you can use to solve problems.

The first two lines of code for determining the note duration are about the same as the code from the previous example program. Now, however, any note could be dotted, which means the duration might have to be multiplied by 1.5. A READ command is used to access values stored in EEPROM by the Dots DATA directive. An IF…THEN statement is used to multiply by 3 and divide by 2 whenever the value of the noteDot variable is 1.

READ Durations + index, noteDuration noteDuration = WholeNote / noteDuration

READ Dots + index, noteDot

IF noteDot = 1 THEN noteDuration = noteDuration * 3 / 2

Page 244 · What’s a Microcontroller?

Integer math The BASIC Stamp does not automatically process a number like 1.5. When performing math, it only works with integers: …, -5, -4, -3, -2, -1, 0, 1, 2, 3, … The best solution for multiplying by 1.5 is to multiply by 3/2. First, multiply by 3, and then divide by 2.

There are many ways to program the BASIC Stamp to handle fractional values. You can program the BASIC Stamp to use integers to figure out the fractional portion of a number. This is introduced in the Basic Analog and Digital Student Guide. There are also two operators that make fractional values easier to work with, and they are: ** and */. These are explained in detail in the Applied Sensors Student Guide and in the BASIC Stamp Manual.

The remainder of this example program works the same way that it did in the previous example program:

FREQOUT 9, noteDuration, noteFreq index = index + 1

LOOP

END

Your Turn – Playing a Tune with More than One Octave

MusicWithMoreFeatures.bs2 made use of rests, but it stayed in one octave. The tune “Take Me Out to the Ball Game” shown below plays most of its notes in the 6th octave. There are two notes in the 7th octave, and they make a big difference to the way it sounds.

√Save the example program under the name MusicWithMoreFeaturesYourTurn.bs2.

√Modify the program by replacing the four data directives and one constant declaration with these:

BeatsPerMin CON 240

√Run the program and verify that it sounds right.

Chapter #8: Frequency and Sound · Page 247

Example Program: SelectCaseWithValues.bs2

√Enter and run SelectCaseWithValues.bs2.

√Click the Debug Terminal’s Transmit Windowpane.

√Enter a value between 0 and 65535, and press the Enter key.

What happens if you enter a number larger than 65535? If you enter the number 65536, the BASIC Stamp will store the number 0. If you enter the number 65537, the BASIC Stamp will store the number 1, and so on. When a number is too large for the variable it fits into, it is called overflow.

√Use Table 2-2 to verify that the example program makes the right decisions about the size of the numbers you enter into the Debug Terminal.

Table 2-2: Variable Types and Values They Can Store

'What's a Microcontroller - SelectCaseWithValues.bs2

'Enter a value and see the minimum variable size required to hold it.

'{$STAMP BS2} '{$PBASIC 2.5}

DEBUG "Enter a value from", CR, "0 to 65535: "

DO

DEBUGIN DEC value

Page 248 · What’s a Microcontroller?

PAUSE 200

CASE 16 TO 255

DEBUG "Byte", CR

PAUSE 300

CASE 256 TO 65535

DEBUG "Word", CR

PAUSE 400

ENDSELECT

DEBUG CR, "Enter another value: "

LOOP

How SelectCaseWithValues.bs2 Works

A word variable is declared to hold the values entered into the Debug Terminal.

value VAR Word

The DEBUGIN command takes the number you enter and places it into the value variable.

DEBUGIN DEC value

The SELECT statement chooses the value variable as the one to evaluate cases for.

SELECT value

The first case is if the value variable equals either 0 or 1. If value equals either of those numbers, the DEBUG and PAUSE commands that follow it are executed.

CASE 0, 1

DEBUG "BIT", CR

PAUSE 100

The second case is if value equals any number from 2 to 15. If it does equal any of those numbers, the DEBUG and PAUSE commands below it are executed.

CASE 2 to 15

DEBUG "NIB (Nibble)", CR

PAUSE 200

When all the cases are done, the ENDSELECT keyword is used to complete the

SELECT..CASE statement.

ENDSELECT

Chapter #8: Frequency and Sound · Page 249

Example Program: SelectCaseWithCharacters.bs2

This example program evaluates each character you enter into the Debug Terminal’s Transmit Windowpane. It can recognize upper and lower case characters, digits, and some punctuation. If you enter a character the program does not recognize, it will tell you to try again (entering a different character).

√Enter and run SelectCaseWithCharacters.bs2.

√Click Debug Terminal’s Transmit Windowpane, enter characters and observe the results.

'What's a Microcontroller - SelectCaseWithCharacters.bs2

'Program that can identify some characters: case, digit, punctuation.

'{$STAMP BS2} '{$PBASIC 2.5}

DEBUG "Enter a character: ", CR

DO

DEBUGIN character

SELECT character

ENDSELECT

DEBUG CR, "Enter another character", CR

LOOP

Page 250 · What’s a Microcontroller?

How SelectCaseWithCharacters.bs2 Works

When compared to SelectCaseWithValues.bs2, this example program has a few differences. First, the name of the value variable was changed to character, and its size was changed from word to byte. This is because all characters in PBASIC are byte size. The SELECT statement chooses the character variable for case by case evaluation.

SELECT character

The quotation marks are used to tell the BASIC Stamp Editor that you are referring to characters.

SELECT character

CASE "A" to "Z"

DEBUG CR, "Upper case", CR

CASE "a" to "z"

DEBUG CR, "Lower case", CR

CASE "0" to "9"

DEBUG CR, "Digit", CR

CASE "!", "?", ".", ","

DEBUG CR, "Punctuation", CR

There is also one different CASE statement that was not used in the previous example:

CASE ELSE

DEBUG CR, "Character not known.", CR, "Try a different one."

This CASE statement tells the SELECT code block what to do if none of the other cases are true. You can get this case to work by entering a character such as % or $.

Your Turn – Selecting Based on Ranges

√Modify the SELECT…CASE statement in SelectCaseWithCharacters.bs2 so that it displays “Special character” when you enter one of these characters: @, #, $, %, ’^’ , &, *, (, ), _, or +.

RTTTL Ringtone Player Application Program

Below is the RTTTL file that contains the musical information used in the next example program. There are five more RTTTL_File DATA directives that you can try in the Your

Chapter #8: Frequency and Sound · Page 251

Turn section. This program plays a tune called Reveille, which is the bugle call played at military camps first thing in the morning. You may have heard it in any number of movies or television shows.

RTTTL_File DATA "Reveille:d=4,o=7,b=140:8g6,8c,16e,16c,8g6,8e,", "8c,16e,16c,8g6,8e,8c,16e,16c,8a6,8c,e,8c,8g6,", "8c,16e,16c,8g6,8e,8c,16e,16c,8g6,8e,8c,16e,", "16c,8g6,8e,c,p,8e,8e,8e,8e,g,8e,8c,8e,8c,8e,8c,", "e,8c,8e,8e,8e,8e,8e,g,8e,8c,8e,8c,8g6,8g6,c."

Example Program: MicroMusicWithRtttl.bs2

This application program is pretty long, and it’s a good idea to download the latest version from the www.parallax.com → Downloads → Educational Curriculum page. Look for a link named Selected Example Programs near the What’s a Microcontroller PDF downloads. Downloading the program and opening it with the BASIC Stamp Editor should save you a significant amount of time. The alternative, of course, is to hand enter and debug four pages of code.

√Use the BASIC Stamp Editor to open your downloaded MicroMusicWithRtttl.bs2 file, or hand enter the example below very carefully.

√Run the program, and verify that the piece is recognizable as the Reveille bugle call.

√Go to the Your Turn section and try some more tunes (RTTTL_File DATA directives).

'What's a Microcontroller - MicroMusicWithRtttl.bs2

'Play Nokia RTTTL format ringtones using DATA.

'{$STAMP BS2}

'{$PBASIC 2.5}

DEBUG "Program Running!"