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

Page 256 · What’s a Microcontroller?

•Constant and variable declarations

•DATA declarations

•READ commands

•IF…ELSE…ENDIF blocks

•DO…LOOP both with and without WHILE and UNTIL

•Subroutines with GOSUB, labels, and RETURN

•FOR…NEXT loops

•LOOKUP and LOOKDOWN commands

•The FREQOUT and PAUSE commands

•SELECT…CASE

Your Turn – Different Tunes

√Try replacing the RTTTL_File DATA directive in MicroMusicWithRTTTL.bs2 with each of the five different music files below.

Only one RTTTL_File DATA directive at a time! Make sure to replace, not add, your new RTTTL_File DATA directive.

√Run MicroMusicWithRTTTL.bs2 to test each RTTTL file.

RTTTL_File DATA "TwinkleTwinkle:d=4,o=7,b=120:c,c,g,g,a,a,2g,f,", "f,e,e,d,d,2c,g,g,f,f,e,e,2d,g,g,f,f,e,e,2d,c,c,", "g,g,a,a,2g,f,f,e,e,d,d,1c"

RTTTL_File DATA "FrereJacques:d=4,o=7,b=125:c,d,e,c,c,d,e,c,e,f", ",2g,e,f,2g,8g,8a,8g,8f,e,c,8g,8a,8g,8f,e,c,c,g6", ",2c,c,g6,2c"

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

RTTTL_File DATA "ForHe'sAJollyGoodFellow:d=4,o=7,b=320:c,2e,e,e,", "d,e,2f.,2e,e,2d,d,d,c,d,2e.,2c,d,2e,e,e,d,e,2f,", "g,2a,a,g,g,g,2f,d,2c"

RTTTL_File DATA "TakeMeOutToTheBallgame:d=4,o=7,b=225:2c6,c,a6,", "g6,e6,2g.6,2d6,p,2c6,c,a6,g6,e6,2g.6,g6,p,p,a6", ",g#6,a6,e6,f6,g6,a6,p,f6,2d6,p,2a6,a6,a6,b6,c,", "d,b6,a6,g6"

Chapter #8: Frequency and Sound · Page 257

Downloading RTTTL Files: There are lots of RTTTL files available for download from various sites on the World Wide Web. These files are contributed by ring-tone enthusiasts, many of whom are not music experts. Some phone tones are pretty good, others are barely recognizable. If you want to download and play some more RTTTL files, make sure to remove any spaces from between characters, then insert the text file between quotes.

Page 258 · What’s a Microcontroller?

SUMMARY

This chapter introduced techniques for making sounds and musical tones using the BASIC Stamp and a piezoelectric speaker. The FREQOUT command can be used to send a piezoelectric speaker high/low signals that cause it to make sound effects and/or musical notes. The FREQOUT command has arguments that control the I/O Pin the signal is sent to, the Duration of the tone, the frequency of the tone (Freq1). The optional Freq2 argument can be used to mix tones.

Sound effects can be made by adjusting the frequency and duration of tones and the pauses between. The value of the frequency can also be swept across a range of values or mixed to create a variety of effects.

Making musical notes also depends on frequency, duration, and pauses. The value of the FREQOUT command’s Duration argument is determined by the tempo of the song and the duration of the note (whole, half, quarter, etc.). The Freq1 value of the note is determined by the note’s letter and octave. Rests between notes are used to set the duration of the PAUSE command.

Playing simple songs using the BASIC Stamp can be done with a sequence of FREQOUT commands, but there are better ways to store and retrieve musical data. DATA directives along with their optional Symbol labels were used to store byte values using no prefix and word values using the Word prefix. The READ command was used to retrieve values stored by DATA directives. The READ command’s Address argument always used the DATA directive’s optional Symbol label to differentiate between different types of data. Some the symbol labels that were used were Notes, Durations, Dots, and Octaves.

Musical data can be stored in formats that lend themselves to translation from sheet music. The sheet music style data can then be converted into Frequency using the LOOKUP and LOOKDOWN commands. Mathematic operations can also be performed on variable values to change the octave of a note by dividing its frequency by a power of two. Mathematic operations are also useful for note durations given either the tempo or the duration of a whole note.

SELECT…CASE was introduced as a way of evaluating a variable on a case by case basis. SELECT…CASE is particularly useful for examining characters or numbers when there are many choices as to what the variable could be and many different sets of actions that

Chapter #8: Frequency and Sound · Page 259

need to be taken based on the variable’s value. A program that converts strings of characters that describe musical tones for cell phones (called RTTTL files) was used to introduce a larger program that makes use of all the programming techniques introduced in this text. SELECT…CASE played a prominent role in this program because it is used to examine characters selected in an RTTTL file on a case-by-case basis.

Questions

1.What causes a tone to sound high-pitched? What causes a tone to sound lowpitched?

2.What does FREQOUT 15, 1000, 3000 do? What effect does each of the numbers have?

3.How can you modify the FREQOUT command from Question 2 so that it sends two frequencies at once?

4.If you strike a piano’s B6 key, what frequency does it send?

5.How do you modify a DATA directive or READ command if you want to store and retrieve word values?

6.Can you have more than one DATA directive? If so, how would you tell a READ command to get data from one or the other DATA directive?

7.What’s an octave? If you know the frequency of a note in one octave, what do you have to do to that frequency to play it in the next higher octave?

8.What does SELECT…CASE do?

Exercises

1.Modify the “Alarm…” tone from ActionTones.bs2 so that the frequency of the tone it plays increases by 500 each time the tone repeats.

2.Explain how to modify MusicWithMoreFeatures.bs2 so that it displays an alert message in the Debug Terminal each time a dotted note is played.

Project

1.Build pushbutton controlled tone generator. If one pushbutton is pressed, the speaker should make a 2 kHz beep for 1/5 of a second. If the other pushbutton is pressed the speaker should make a 3 kHz beep for 1/10 of a second.

Page 260 · What’s a Microcontroller?

Solutions

Q1. Our ears detect changes in air pressure as tones. A high pitched tone is from faster changes in air pressure, a low pitched tone from slower changes in air pressure.

Q2. FREQOUT 15, 1000, 3000 sends a 3000 Hz signal out pin 15 for one second (1000 ms).

The effect of each number: 15 – pin number 15.

1000 – duration of tone equals 1000 ms or one second.

3000 – the frequency of the tone, in Hertz, so this sends a 3000 Hz tone.

Q3. Use the optional Freq2 argument. To mix 3000 Hz and say, 2000 Hz, we simply add the second frequency to the command, after a comma:

FREQOUT 15, 1000, 3000, 2000

Q4. 1975.5 Hz, see Figure 8-3 on page 228.

Q5. Use the optional Word modifier before each data item.

Q6. Yes. Each DATA directive has a different symbol parameter. To specify which DATA directive to get the data from, include the symbol parameter after the READ keyword. For example: READ Notes, noteLetter. In this example, Notes is the symbol parameter.

Q7. An octave is a group of 8 whole and 4 chromatic notes. To get a given note in the next higher octave, multiply the frequency by two.

Q8. SELECT...CASE selects a variable or expression, evaluates it on a case by case basis, and executes different blocks of code depending on which case the variable's value fits into.

E1. This problem can be solved either by manually increasing each tone by 500, or by utilizing a FOR...NEXT loop with a STEP value of 500.

E2. Modify the lines that check for the dotted note:

READ Dots + index, noteDot

Chapter #8: Frequency and Sound · Page 261

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

Add a DEBUG command to the IF...THEN. Don't forget the ENDIF.

READ Dots + index, noteDot IF noteDot = 1 THEN

noteDuration = noteDuration * 3 / 2 DEBUG "Dotted Note!", CR

ENDIF

P1. Use the piezospeaker circuit from Figure 8-2, p. 220; pushbutton circuits from Figure 4-20, p. 129.

'What's a Microcontroller - Ch8Prj01_PushButtonToneGenerator.bs2

'P4 Pressed: 2 kHz beep for 1/5 second. 2 kHz = 2000 Hz.

'1/5 s = 1000 / 5 ms = 200 ms

'P3 Pressed: 3 kHz beep for 1/10 second. 3 kHz = 3000 Hz.

'1/10 s = 1000 / 10 ms = 100 ms

'{$STAMP BS2}

'{$PBASIC 2.5}

DEBUG "Program Running!"

Further Investigation

“Applied Sensors”, Student Guide, Version 2.0, Parallax Inc., 2003

More sound effects, clicks, crickets are introduced using the piezoelectric speaker. The pentatonic and equal temperament scale are the basis for discussion of math fractions. The speaker is also used as feedback for a variety of sensor measurements.

“Basic Analog and Digital”, Student Guide, Version 2.0, Parallax Inc., 2003

The speaker is used to make a frequency generated by a 555 timer audible. The BASIC Stamp measures the frequency of the tone with a COUNT command.

“Understanding Signals”, Student Guide, Version 1.0, Parallax Inc., 2003

You can use this book to view the output of the FREQOUT command, both as digital pulses, and as sine waves.

Chapter #9: Electronic Building Blocks · Page 263

Chapter #9: Electronic Building Blocks

THOSE LITTLE BLACK CHIPS

You need look no further than your BASIC Stamp (see Figure 9-1) to find examples of “those little black chips”. Each of these chips has a special function. The upper-right chip is the voltage regulator. This chip takes the battery voltage and converts it to almost exactly 5.0 V, which is what the rest of the components on the BASIC Stamp need to run properly. The upper-left chip is the BASIC Stamp module’s EEPROM. PBASIC programs are condensed to numbers called tokens that are downloaded to the BASIC Stamp. These tokens are stored in the EEPROM, and you can view them by clicking Run and then Memory Map in the BASIC Stamp Editor. The largest chip is called the Interpreter chip. It fetches the tokens from the EEPROM and then interprets the PBASIC command that the token represents. Then, it executes the command, fetches the next token, and so on. This process is called “fetch and execute”.

Figure 9-1

Integrated

Circuits on the

BASIC Stamp