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5x7 Display
Piezo Experiments
Page1
EXPERIMENT-1P
Making a Tone
This experiment demonstrates how to
create a tone from a piezo. A Piezo is very similar to a 22n capacitor as
far as the circuit is concerned and the micro sees the piezo as a capacitor.
In other words it does not see it a resistive load. In fact it is not a load
but a small amount of effort is required to send energy into the capacitor
and then "drain it out." When this is done thousands of times a
second, the end result is small amount of energy is required. When a voltage is delivered to the piezo, a thin white crystal substance
between two plates sees this voltage and expands. Since it is glued to one
side of a thin sheet of metal, it make the side of the metal expand and this
"dishes" the metal. When the crystal substrate sees no voltage or
a reverse voltage, it shrinks and this flattens or reverses the metal disk.
If this is repeated fast enough, the result is a horrible, tinny sound that
we have come to know as a "piezo squeal." As the pulse-rate
increases, the output frequency of the piezo increases and a point is
reached when the output increases enormously. This is the "resonant
frequency" of the piezo and that is why some piezos give an extremely loud
output. They are not only "good quality" piezos but are operating
at their optimum frequency.
The program below produces a tone of approx 500Hz from the piezo.
The delay routine consists of 255 loops of decrementing file 1A. This file
does not have to be loaded with a value if you want 255 decrements as the
file is decremented first then tested and thus it starts at 255 at the
beginning of decrementing.
The circuit for "5x7 Display" is shown below:
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Experiment-1P
for "Piezo on 5x7 Display" Project
;PIC16F84 and only F84 chip
;Creating a tone
Start ORG 0x00
BSF 03,5
;Go to page1 for setting-up the ports
MOVLW 00h
;Put 00 into W
MOVWF 05h
; to make all RA lines output
MOVWF 06h
;to make all RB lines output
BCF 03,5
;Go to Page0 for programming
Tone1 BSF 06,7
;this is the piezo line. Turn it ON
CALL Delay
;Call Delay
BCF 06,7
;Turn off the piezo
CALL Delay
;Call Delay
GOTO Tone1
;Repeat the routine
Delay DECFSZ 1Ah,1
;Delay for tone
GOTO Delay
RETURN
END
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| The block of
numbers below is the HEX file for Experiment-1P. Copy and paste
it into a text program such as TEXTPAD or NOTEPAD and call it: Expt-1P.hex
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:100000008316003085008600831286170A20861327
:0A0010000A2005289A0B0A280800B0
:00000001FF |
EXPERIMENT-2P
Producing
a beep
This experiment produces a beep. It
is repeated every second.
One of the biggest problems with
creating a tone or a beep is the computer-time taken up. As you can see from the
program, a tone (or beep) is created by turning ON an output, calling a
delay routine, then turning the piezo OFF. Even though it takes only one
instruction to turn the piezo on or off, the delay between each operation
is fairly short and quite often the program is required to concentrate on
producing the beep. This is ok if the beep is very short as the routine
can be hidden inside a longer delay that may be displaying a column of LEDs,
for example, or during the time when the screen is blanked.
If you want to scan the screen while producing a tone tone at the same time,
you have to integrate two routines and execute them at the same time. This is
very difficult to do as you must know exactly the length of the second
routine so that the tone has the correct frequency. The second routine
cannot have any variation in its length as this will alter the frequency.
The routine below produces a beep . . . beep . . .beep . . beep . . .
from the piezo.
4 loops i.e: 4 delay routines are needed to produce the effect. The first
delay routine is needed after the piezo has been turned on. The second delay
routine is needed after the piezo has been turned off. This action has to be
repeated to actually produce a tone as the operation of turning the piezo on
and then off does not produce a tone. It's only when this is repeated many
times in a short period of time that the sound is generated.
The piezo is connected to the micro via a buffer transistor so that a choke
can be added to the circuit to increase the sound output. The piezo-circuit
must not be left ON after a tone is emitted as the circit takes a very high
current in the ON condition.
If you want the piezo to be louder, a choke can be added to the board as marked, in
place of the 1k resistor.
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Experiment-2P
for Piezo on "5x7 Display" Project
;PIC16F84 and only F84 chip
;Creating a beep - beep - beep
Start ORG 0x00
BSF 03,5
;Go to page1 for setting-up the ports
MOVLW 00h
;Put 00 into W
MOVWF 05h
; to make all RA lines output
MOVWF 06h
;to make all RB lines output
BCF 03,5
;Go to Page0 for programming
Beep MOVLW 40h
MOVWF 1Bh
Beep1 BSF 06,7
;This is the piezo line. Turn it ON
CALL Delay
;Call Delay
BCF 06,7
;Turn off the piezo
CALL Delay
DECFSZ 1Bh,1
;Repeat for 40h cycles
GOTO Beep1
CALL LongDel
;Call Long Delay
GOTO Beep
;Repeat the routine
Delay
MOVLW 40h
MOVWF 1Ah
Delay1 DECFSZ 1Ah,1
;Delay for Beep
GOTO Delay1
RETURN
LongDel MOVLW 04
;Long delay between beeps
MOVWF 1Ch
Del2 DECFSZ 1Ah,1
GOTO Del2
DECFSZ 1Bh,1
GOTO Del2
DECFSZ 1Ch,1
GOTO Del2
RETURN
END
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| The block of
numbers below is the HEX file for Experiment-2P. Copy and paste
it into a text program such as TEXTPAD or NOTEPAD and call it: Expt-2P.hex
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:100000008316003085008600831240309B008617DF
:100010000F2086130F209B0B072814200528403043
:100020009A009A0B1128080004309C009A0B16289D
:0A0030009B0B16289C0B16280800F5
:00000001FF |
EXPERIMENT-3P Beep after
Button A, B and C
This experiment produces a beep after button A is pressed two beeps
after button B is pressed, and three beeps for button C. (The program
would be much simpler if only a single beep is required.)
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Experiment-3P
for Piezo on "5x7 Display" Project
;PIC16F84 and only F84 chip
;Beep after
Button A, B and C
Start ORG 0x00
BSF 03,5
;Go to page1 for setting-up the ports
MOVLW 00h
;Put 00 into W
MOVLW 1C
;Put 0001 1100 into W
MOVWF 05h
;make RA2, RA3 and RA4 input
MOVLW 00h
MOVWF 06h
;make all RB lines output
BCF 03,5
;Go to Page0 for programming
GOTO Main
SwA BTFSS 05,2
;Is switch A pushed?
GOTO SwA2
;YES.
MOVF 11h,0
;NO. Copy 11h into W
XORLW 00h
;XOR W with 00
BTFSS 03,2
;Is file 11h=0?
GOTO SwA1
;NO.
RETURN
;YES.
SwA1 DECF 11h,1
;Decrement the debounce file
RETURN
SwA2 MOVF 11h,0
;11h is the debounce file
XORLW 00h ;
BTFSS 03,2
;Is file 11h=0?
RETURN
;NO.
CALL Beep1
;YES.
MOVLW 80h
;Load W with 80h loops
MOVWF 11h
;Put 80h into debounce file
RETURN
SwB BTFSS 05,3
;Is switch B pushed?
GOTO SwB2
;YES.
MOVF 12h,0
;NO. Copy 12h into W
XORLW 00h
;XOR W with 00
BTFSS 03,2
;Is file 12h=0?
GOTO SwB1
;NO.
RETURN
;YES.
SwB1 DECF 12h,1
;Decrement the debounce file
RETURN
SwB2 MOVF 12h,0
;12h is the debounce file
XORLW 00h ;
BTFSS 03,2
;Is file 12h=0?
RETURN ;NO.
CALL Beep2
;YES.
MOVLW 80h
;Load W with 80h loops
MOVWF 12h
;Put 80h into debounce file
RETURN
SwC BTFSS 05,4
;Is switch C pushed?
GOTO SwC2
;YES.
MOVF 13h,0
;NO. Copy 13h into W
XORLW 00h
;XOR W with 00
BTFSS 03,2
;Is file 13h=0?
GOTO SwC1
;NO.
RETURN ;YES.
SwC1 DECF 13h,1
;Decrement the debounce file
RETURN
SwC2 MOVF 13h,0
;13h is the debounce file
XORLW 00h ;
BTFSS 03,2
;Is file 1Dh=0?
RETURN ;NO.
CALL Beep3
;YES.
MOVLW 80h
;Load W with 80h loops
MOVWF 13h
;Put 80h into debounce file
RETURN
Beep1 MOVLW 40h
MOVWF 1Bh
Beepx BSF 06,7
;This is the piezo line. Turn it ON
CALL Delay
;Call Delay
BCF 06,7
;Turn off the piezo
CALL Delay
DECFSZ 1Bh,1
;Repeat for 40h cycles
GOTO Beepx
RETURN
Beep2 CALL Beep1
CALL LongDel
CALL Beep1
RETURN
Beep3 CALL Beep1
CALL LongDel
CALL Beep1
CALL LongDel
CALL Beep1
RETURN
Delay MOVLW 30h
MOVWF 1Ah
Delay1 DECFSZ 1Ah,1 ;Delay for Beep
GOTO Delay1
RETURN
LongDel MOVLW 01
MOVWF 1Ch
Del2 DECFSZ 1Ah,1
GOTO Del2
DECFSZ 1Bh,1
GOTO Del2
DECFSZ 1Ch,1
GOTO Del2
RETURN
Main CALL SwA
CALL SwB
CALL SwC
GOTO Main
END
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| The block of
numbers below is the HEX file for Experiment-3P. Copy and paste
it into a text program such as TEXTPAD or NOTEPAD and call it: Expt-3P.hex
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:10000000831600301C3085000030860083125C2887
:10001000051D11281108003A031D0F28080091033F
:1000200008001108003A031D08003B2080309100B1
:100030000800851D22281208003A031D2028080008
:10004000920308001208003A031D08004420803083
:1000500092000800051E33281308003A031D3128BA
:100060000800930308001308003A031D0800482005
:1000700080309300080040309B0086174E20861386
:100080004E209B0B3D2808003B2053203B200800BE
:100090003B2053203B2053203B20080030309A0067
:1000A0009A0B5028080001309C009A0B55289B0B96
:1000B00055289C0B55280800082019202A205C2868
:00000001FF |
EXPERIMENT-4P
Hee Haw
Siren
This experiment produces a Hee Haw siren suitable for an alarm. The
first column of LEDs flash in sequence with the sound.
This is the simplest routine you can get for a Hee Haw effect. So, why is it so
complex?
Let's explain:
The Hee routine is exactly the same as the Haw routine except the length of
the ON and OFF time is longer so that the tone has a lower frequency.
If we take the Hee routine, we first have to turn ON all the LEDs. Next we
find a nested routine made up of two files (file 1C and 1B). We need two
files because one file will not produce a tone for a long enough period and
the final result is a very fast Hee Haw sound. With two files we can make a
very slow Hee Haw.
Next we come to two instructions that toggle the piezo line. It does not
matter if the line is originally HIGH or LOW. The two instructions change
the state of the line.
This means we can loop around these two instructions and each time the micro
passes, the piezo will turn ON or OFF.
After this we load the delay file with a value and call the delay so that
the piezo line is HIGH (or LOW) for quite a few thousand cycles. This will
produce the actual tone and the files around these instructions produce the
duration of the tone.
Once the duration of the LOW frequency (the Hee tone) has ended, the LEDs
are turned off and the Haw tone is executed.
Once you understand these basics, routines like this will be taken from a
Library of Routines and CALLed. But it's important to know how they work so
that individual features can be altered as necessary. You may require to
increase one of the tones, or produce the tone for 25 repetitions and STOP,
or call the routine when certain conditions have occurred.
Nothing is standard in programming. You are always required to meet certain
criteria with each program and you must know the absolute basics with
everything you write. And that's what we are doing in these
experiments.
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Experiment-4P
for Piezo on "5x7 Display" Project
;PIC16F84
;Hee Haw
Siren with flashing LEDs
Start ORG 0x00
BSF 03,5
;Go to page1 for setting-up the ports
MOVLW 00h
;Put 00 into W
MOVWF 05h
; to make all RA lines output
MOVWF 06h
;to make all RB lines output
BCF 03,5
;Go to Page0 for programming
;Hee - this is the LOW frequency
Hee MOVLW 0FFh
MOVWF 06
;Turn ON all LEDs
MOVLW 04
MOVWF 1C
Hee1 MOVLW 080h
MOVWF 1B
Hee2 MOVLW 80h
;Toggle the piezo line.
XORWF 06h,1
MOVLW 0B0h
MOVWF 1Ah
CALL Delay
;Call Delay
DECFSZ 1B,1
GOTO Hee2
;Repeat the routine as per file 1B
DECFSZ 1C,1
GOTO Hee1
;Haw - This is the HIGH frequency
Haw MOVLW 00
MOVWF 06
;Turn OFF all LEDs
MOVLW 04
MOVWF 1C
Haw1 MOVLW 0D0h
;Create D0 loops
MOVWF 1B
Haw2 MOVLW 80h
;Toggle the piezo line.
XORWF 06h,1
MOVLW 80h
MOVWF 1Ah
CALL Delay
;Call Delay
DECFSZ 1B,1
GOTO Haw2
;Repeat the routine as per file 1B
DECFSZ 1C,1
GOTO Haw1
GOTO Hee
Delay DECFSZ 1Ah,1
;Length of ON and OFF time for tone
GOTO Delay
RETURN
END
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| The block of
numbers below is the HEX file for Experiment-4P. Copy and paste
it into a text program such as TEXTPAD or NOTEPAD and call it: Expt-4P.hex
|
|
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:1000000083160030850086008312FF30860004309E
:100010009C0080309B0080308606B0309A002420FF
:100020009B0B0B289C0B09280030860004309C0099
:10003000D0309B008030860680309A0024209B0BB5
:0E0040001A289C0B182805289A0B2428080063
:00000001FF |
On the next page we show how to CALL the Hee Haw routine. Go
to the next page of experiments:
5x7 PIEZO
EXPERIMENTS: Page-2
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