Whats A Microcontroller v3

Frequency and Sound · Page 271

Those two notes in the 7th octave are essential for making the tune sound right. It’s interesting to hear what happens if those 7 values are changed to 6.

9Try changing the two 7 values in the Octaves DATA directive so that they are 6. Keep in mind, this will make “Take Me out to the Ball Game” sound weird.

9Run the program, and listen to the effect of the wrong octaves on the song.

9Change the Octaves DATA back to its original state.

9Run the program again and listen to see if it sounds correct again.

ACTIVITY #5: RINGTONES WITH RTTTL

Older cell phones used to play ringtones with a piezospeaker. Ringtones were downloaded from the web to a computer, and then uploaded from the computer to the cell phone’s microcontroller. At the time, one of the most widely used ways of composing, recording and posting ringtones was one that featured strings of text with characters that describe each note in the song. Here is an example of how the first few notes from “Beethoven’s 5th” look in one of these strings:

Beethoven5:d=8,o=7,b=125:g,g,g,2d#,p,f,f,f,2d

This format for storing musical data is called RTTTL, which stands for Ringing Tone Text Transfer Language. The great thing about RTTTL files at the time was that they were widely shared via the World Wide Web. Many sites had RTTTL files available for free download. There were also free software programs that could be used to compose and emulate these files as well as upload them to your cell phone. The RTTTL specification is still published online. Appendix C summarizes how an RTTTL file stores notes, durations, pauses, tempo, and dotted notes.

This activity introduces some PBASIC programming techniques that can be used to recognize different elements of text. The ability to recognize different characters or groups of characters and take action based on what those characters contain is extremely useful. In fact, it’s the key to converting an RTTTL format ringtone (like Beethoven5 above) into music. At the end of this activity, there is an application program that you can use to play RTTTL format ringtones.

Selecting which Code Block to Execute on a Case by Case Basis

The SELECT...CASE statement is probably the best programming tool for recognizing characters or values. Keep in mind that this is one of the tools used to convert an RTTTL ringtone into musical notes.

Page 272 · What’s a Microcontroller?

In general, SELECT...CASE is used to:

•Select a variable or expression.

•Evaluate that variable or expression on a case by case basis.

•Execute different blocks of code depending on which case that variable’s value fits into.

You can try the next two example programs to see how SELECT...CASE works. SelectCaseWithValues.bs2 takes numeric values you enter into the Debug Terminal and tells you the minimum variable size you will need to hold that value. SelectCaseWithCharacters.bs2 tells you whether the character you entered into the Debug Terminal is upper or lower case, a digit, or punctuation.

Remember to use the Transmit windowpane in the Debug Terminal to send the characters you type to the BASIC Stamp. The Transmit and Receive windowpanes are shown in Figure 8-5.

or characters you want to transmit to the BASIC Stamp.

Example Program: SelectCaseWithValues.bs2

9Enter and run SelectCaseWithValues.bs2.

9In the Debug Terminal, make sure that the Echo Off checkbox is clear (no checkmark).

Frequency and Sound · Page 273

9Click the Debug Terminal’s Transmit windowpane.

9Enter 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.

9Use Table 8-1 to verify that the example program makes the right decisions about the size of the numbers you enter into the Debug Terminal.

Table 8-1: 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}

DO

DEBUGIN DEC value

SELECT value

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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.

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

Frequency and Sound · Page 275

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).

9Enter and run SelectCaseWithCharacters.bs2.

9Make sure the Echo Off checkbox is clear (no checkmark).

9Click the Debug Terminal’s Transmit windowpane to place the cursor there.

9Enter characters into the Transmit windowpane and observe the results.

'What's a Microcontroller - SelectCaseWithCharacters.bs2

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

PAUSE 1000

DEBUG "Enter a character: ", CR

DO

DEBUGIN character

SELECT character

ENDSELECT

DEBUG CR, "Enter another character", CR

LOOP

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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. We can treat the following groups of characters and punctuation marks the same way as a range of numbers, since the BASIC Stamp recognizes them by their ASCII numeric equivalents—see the ASCII chart in the BASIC Stamp Editor Help.

SELECT character

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 Special Characters

9Modify the SELECT...CASE statement in SelectCaseWithCharacters.bs2 so that it displays “Special character” when you enter one of these characters: @, #, $, %, ’^’ , &, *, (, ), _, or +.

Frequency and Sound · Page 277

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 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/go/WAM page. 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.

9With the BASIC Stamp Editor, open your downloaded MicroMusicWithRtttl.bs2 file, or hand enter the example below very carefully.

9Run the program, and verify that the piece is recognizable as the Reveille bugle call.

9Go 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!"

duration = duration * 10 + char - 48