Frequency and Sound

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Chapter 8

• Frequency and Sound
• only covers through Twinkle Twinkle Little Star
• (opt)can skip to boe bot at this point

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Electric Beeps

• From your alarm clock to microwave to automobiles
  and ATM machines your day is full of devices
  sounding beeps to alert you or indicate actions
  to be taken.
• Microcontrollers produce sounds by sending
  high/low signals very quickly to a speaker. The
  rate at which the signal repeats is called
  frequency and is measured in cycles per second or
  Hertz (Hz) which produce the desired tone or
  pitch.

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How conventional speakers work

• http//electronics.howstuffworks.com/speaker6.htm
• See function generator and speaker demonstration

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Piezoelectric Speaker

• The piezoelectric speaker is a common, small and
  inexpensive speaker used in many devices though
  it lacks in audio quality.

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How Piezoelectric Materials Work

• In a crystal microphone, air pressure deforms the
  crystal enough to cause very small voltage
  changes in the crystal. These voltage changes are
  amplified and used to record or transmit sounds.
• Piezoelectric materials also work the other way.
  If you apply a voltage across the crystal, the
  crystal will change shape. The change is very
  slight in most cases, but it is enough to drive
  small speakers.

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ACTIVITY 1 Building and Testing the Speaker
Build the circuit below
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Enter, Run, and Save the code below

• The FREQOUT command sends high/low signals to the
  specified pin at the frequency and for the
  duration defined.FREQOUT Pin, Duration, Freq1,
  Freq2
• To play a note at 2000Hz which lasts 1.5 seconds
  (1500ms)

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Your turnadjusting frequency and duration

• Save the program under a new name
• Try some different values for Duration and Freq1
• Notice as the frequency gets higher so does the
  pitch observed

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Some interesting sounds can be done with for next
loops

• Run RAY GUN on the next slide

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Use the Reset button for your trigger
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Enter, Run, and Save Actiontones.bs2 on the next
slide (page 222 of your text)
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• In ActionTones.bs2 a variety of tones are played.
  Alarm and Robot Reply are a sequence of tones
  sent to the speaker.
• In Hyperspace, a nested loop is used where
  FREQOUT cycles through durations from 15 to 1.
  For each duration it cycles through frequencies
  from 2000 to 2500 in increments of 20.

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Nested Loops
Inner Loop
Outer Loop
The inner loop is performed fully
everyrepetition of the outer loop.
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What follows are some sound effects that are
based on nested loops
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Enter, Run, and Save the code below (PROGRAM 3)

• Use your eyes and ears to verify that
• Duration changes each pass through the outer loop
• Frequency changes each pass through the inner loop

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Enter, Run, and Save the code below under the
name actiontonesyourturn.bs2
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Beats

• Produced by two slightly different frequencies
  played at the same time
• Beat Frequency difference between the
  frequencies
• http//www.walter-fendt.de/ph14e/beats.htm

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Two Frequencies at Once

• The FREQOUT command has an optional parameter
  called Freq2. This allows playing 2 frequencies
  simultaneously.
• At times the frequencies will be in phase and at
  other times be out of phase creating a beat
  frequency. This rate of being in then out of
  phase difference in frequencies
• FREQOUT 9, 5000, 2000, 2005

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Enter, Run, and save mixingtones.bs2 below
(page 226 of your text)

• Note a beat frequency is the rate at which the
  two frequencies fade in and out
• Beat frequency difference in frequencies
• BF 2 Hz produced by mixing 2000 Hz with 2002 Hz
• BF 4 Hz produced by mixing 2000 Hz with 2004 Hz

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This code is inefficient and we can do better

• Modify the code, so the same task is done using a
  word variable and a loop
• MY SOLUTION IS ON THE NEXT SLIDE

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ACTIVITY 3 Musical Notes and Simple Songs

• Each key on a piano is a specific frequency
  corresponding to a note. There are 12 groups of
  notes, each at a higher octave. An octave is a
  doubling of frequency, so C7 is double the
  frequency of C6. C8 2 x C7etc

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DO RE ME FA SO LA TI DO (C6) (D6) (E6) (F6) (G6) (
A6) (B6) (C7) THIS IS DONE BY PLAYING JUST THE
WHITE OR NATUARL KEYS
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• The black keys are called sharps or flats
• C6 D6b
• A6 B6b

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See if you can make your microcontroller play do
re me fa so la ti dowith a 500 ms pause between
each note. Save your code as doremefasolatido.bs2

• Use page 229 for help if you like

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Try some modifications

• Try Including the sharp and flat notes in your
  song
• Next play the song at the next octave up
• Freq2 might save you some time

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Storing and Retrieving Data

• The DATA command allows us to save musical or any
  other type of data in the bs2 EEPROM.
• The syntax is as follows
• Symbol DATA Word DataItem1,DataItem2,
• For exampleNotes DATA "C","C","G","G","A","A","G
  "Stores the characters in EEPROM, with the 1st
  location called Notes. Each subsequent address
  is Notes an index value.0,1,2,3 etc

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Notes DATA "C","C","G","G","A","A","G"

• The first letter C is at notes 0
• The second letter C is at notes 1
• G is at notes 2
• etc

Note When storing letters, you must place
quotations around the letters. This is not
necessary for numbers
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Using memory map

• Each location on the memory map can store one
  byte (8 bits) (8 digits) so up to a decimal
  value of 255
• Two bytes would be a word value (256 to 65535)
  and would take up two locations on the memory map
• The memory map uses a grid in hex to mark the
  location of each of these registers
• Lets enter some numbers in the eeprom with the
  data command.
• Note that when entering word values, two
  registers are taken instead of just one
• See next slide

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• Notice only five registers in EEPROM are taken
  up.starting with register 0

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• However, here 6 registers in EEPROM are taken
• NOTE you must tell eeprom if you plan on
  storing a value greater than 255 by stating that
  this data piece is a word

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Pulling the stored data from the EEPROM with
READ

• Lets say we want to pull the data out of eeprom
  that we stored in it with
• Notes DATA "C","C","G","G","A","A","G"
• SYNTAX
• READ Notes 6,noteletter
• This means find the data stored in the 6 th
  register of EEPROM and store it under the
  variable noteletter
• If you like, you can now debug the value of
  noteletter to see if it is correct
• Try this71 is ascii for the letter G

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Reading words from EEPROM

• Remember, data stored as word variables take up
  two registers in eeprom
• Lets say we have
• Numbers DATA word 2000, word 3000
• Now lets display the second stored number in the
  debug terminal
• READ numbers 2,Word value
• DEBUG ?value
• ..2000 takes up registers 0 and 13000 takes up
  registers 2 and 3..also notice the presence of
  word in front of value!!!!

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Store a song in memory

• Use two Data commands to store
• The letters in doremefasolatido
• The frequencies in doremefasolatido
• Your program should
• Display the noteletters and the frequencies in
  the debug terminal while the song is played

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Enter, Run, and Save the code on the next slide
(page 231 of your text)
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TwinkleTwinkle.bs2 Abbreviated version
When index 0
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• Verify that the notes sound like the song Twinkle
  Twinkle Little Star
• Use the Debug terminal to verify that it works as
  expected by accessing and displaying values from
  the three DATA directives

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• Now modify the song, so it plays the second part
  of the tune
• As in the first phrase the last note is held
  twice as long as the others
• You will need to expand each data directive
• You will need to change the FORNEXT loop so it
  goes from 0 to 13 instead of 0 to 6.
• TRY IT!!

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A HELPFUL WEB SITE FOR THE PROJECTS THAT FOLLOW

• THE ONLINE KEYBOARD
• http//www.pianoworld.com/fun/javapiano/javapiano.
  htm