Kits are available for this project from Talking Electronics for $10.00 plus postage.
Plus you will need:
6pin to 5pin adapter @ $2.50

You will also need:
Chip Programmer - PICkit2 from Modtronix
(MPASM and MPLAB come with PICkit2)
and it includes USB lead

PIC12F629 Data Sheet (.pdf  4,926KB)
Instruction Set for PIC12F629
blank12F629.asm template


See more projects using micros:
Elektor,EPE,Silicon Chip

Notepad2.zip     Notepad2.exe 
Library of Sub-routines "Cut and Paste
Library of routines:   A-E   E-P    P-Z 


Why spend $2 on a "Whistle Key Finder" when you can spend $10.00 on producing your own design?


Because you don't learn anything when you buy the $2.00 device.

Whistle Key Finder on prototype board
The piezo has been moved slightly to show the surface-mount components.
The 5 pins on the left are for In-Circuit Programming.
The coin holder positive has been bent to hold 3 button cells
The LED on the lower corner was used to test the chip.

This project uses one of the smallest chips in the PIC microcontroller range, the PIC12F629 and you can learn to program it and experience the thrill of making something yourself and see what goes into writing a program.
Even a program as simple as this one is not easy to put together and if you are starting from scratch, you will need a programmer (a "burner") and all the data that goes with "burning" and creating a program for the micro. We use the PICkit-2 as it is the cheapest and best. It comes with USB cable and 2 CD's containing the programs needed to "burn" the chip. You will also need NotePad2 to write your .asm program
(use Whistle.asm or Whistle.txt as a template for your program).

The PC board includes 5 pins for "In Circuit Programming" via PICkit-2 and you will be encouraged to use surface-mount components to interface the piezo diaphragm to the chip.
One of the clever parts of the circuit is the piezo is used to detect the sound and then produce the beep-beep-beep reply.
Be reminded that not all piezo diaphragms are the same. Some are very sensitive when detecting audio and others are not sensitive at all.
Ours produces an output of about 20mV to 50mV when whistling up-close, while an insensitive diaphragm will produce only a few millivolts.

The circuit consists of two common-emitter stages with enough gain to produce a rail-to-rail signal when the piezo detects a whistle.
We are not concerned about distortion or over-driving the chip as we want a fairly square wave.
A super-alpha arrangement was tried using two transistors but it did not work at all.
It is surprising how "theory" does not always work in practice and that's why you must try everything before settling on a result. Each stage has a gain of approx 70, making the total approx 5,000. This allows a 1mV signal from the piezo to produce a rail-to-rail waveform.
As we mentioned, the interesting feature of the circuit is the use of the piezo to detect a signal and then produce a beep. This has been done by making the piezo "float."
It is not connected to any rail and although it is connected to pins of the chip, these can be made "inputs" and thus become high impedance.
The 4k7 on the base of the transistor allows the piezo to be driven by the chip in "bridge-mode" where the pins are alternately made high then low so that twice the supply voltage is effectively delivered across the piezo to increase its output.
Without the 4k7, the lead of the piezo would not rise above 0.6v due to the base-emitter voltage limitation.
When the piezo is required to detect a signal, one lead is connected to 0v via a pin of the chip and the other lead connects to the base via the 4k7. The pin on the chip is changed to "input" during this operation.
When the piezo is activated, the signal is also amplified through the transistors but the chip is not in detection-mode and this signal is not detected.

To keep in line with miniaturisation, we have used surface-mount components. Once you start using surface-mount components, you get hooked. Through-hole components seem enormous. You will need fine tweezers to hold them in place while one end is soldered.
Always use very fine solder as you only need very little for each component and the main reason for adding extra is to take advantage of the flux to clean the connection. Always solder resistors with the value showing. Capacitors don't have values marked on them and you cannot work out the value by the size of the component.
That's why you have to know the value before taking them out of their "carrier."

You can build the circuit on any type of PC board and we have used a small prototype board that needs some of the tracks cut to suit the placement of the 8 pin IC socket.
The kit of components comes with all the parts you need to get the project working, including a pre-programmed chip and a prototype PC board that needs some tracks cut.
We will not describe any construction details as most constructors will be adept in placing components. The only thing to remember is to cut the tracks before fitting the IC socket as some tracks run under the socket.
To modify the program you will need a PICkit-2 programmer and this comes with 2 CD's containing all the software needed for In-Circuit Programming.
You will also need a lead to connect the programmer to your lap top via the USB port (comes with PICkit-2) and an adapter we call a 6pin to 5 pin Adapter to connect the PICkit-2 to your project. (The photo below shows the prototype 6pin to 5 pin Adapter. A PC board is now available for the adapter.)

6pin to 5pin Adapter

PICkit-2 and Adapter connected for In-Circuit Programming

The program detects the signal from the diaphragm and only processes a waveform that falls in the 2kHz region. A 2kHz signal has a period of  1,000,000 / 2,000 = 500uS. The period of a waveform is the time taken to travel from the 0v level to the maximum (positive), then to the max negative and back to the 0v level. Of course this time is also the distance between two peaks but it is more convenient to describe it in our terms (starting at the 0v level).
This means the time when the signal will be HIGH will be 250uS and 250uS for a LOW.
If we take the HIGH portion, we can "open the gate of the chip" by making a pin INPUT and looking at that pin to see if it is HIGH. The signal will create a HIGH on the pin.
We create a very short-duration loop to look for a HIGH and when it is detected, we delay nearly 250uS and see if it is still HIGH.
A short time after this, the signal should be LOW and if this is the case, we look for a LOW of about 250us and see if the signal becomes HIGH just after 250uS.
This is the principle of looking for a 2kHz signal and we have allowed for a "look" just slightly before and after 250uS to cater for frequencies just slightly above and below 2kHz. Each time the micro detects a high and low, it increments a file called "count."
Now, there's what is also happening:
We are only looking for a signal for about 100mS (100,000uS) and this "time-delay" is done in the background via a set of registers that are incremented by the clock in the PIC chip.
When the registers fill and roll over, the micro leaves the section it is executing and goes to a sub-routine called "isr."  This is the Interrupt Service Routine and it tells the micro to go to Main2 where the number of cycles stored in the "count" file is released as beeps from the piezo.
But first, only values in the high nibble in the "count" file are used. The nibbles are swapped so that the value in the upper 4 bits will be used. The register is then shifted two places to the right so that the two top bits appear in the lowest places in the register. The register is then masked to get only the two lowest bits. This produces 1, 2, 3 or 4 beeps.
Finally, the program has a delay in the "isr" that makes the micro beep 3 times after approx 1-minute of non-detection.
The most difficult part of the program is detecting a narrow band of frequency. We have done this in the section "aa" to "dd" but it can be improved and it is your job to narrow this filter and only detect a whistle.

The micro loops around the instructions contained at "aa,"  "bb,"  "cc,"  "dd" and when the 131,072uS has been reached, the micro goes to address 4 where it finds the instruction to go to isr. This is how it gets out of the loop.

Another important feature of this program is the coverage of the INTERRUPT routine.
To enable the micro to count in the background then go to the interrupt location (address 4), requires a number of bits to be set in a number of files. The setting of these bits in the various files is shown in "Main."
When you are creating another project that requires similar "counting in the background," you will be able to "cut and paste" the code. (Point to remember: Timer0 does not produce a long delay, so Timer1 has to be used).

Here are the files you will need:


	;Whistle (Key Finder) 12F629.asm
	;  9-7-2009  

	list	p=12f629
	radix	dec
	include	"p12f629.inc"
	errorlevel	-302	; Don't complain about BANK 1 
				;  Registers during assembly

			& _WDT_OFF & _INTRC_OSC_NOCLKOUT  ;Internal osc.

	;Files for 12F629 start at 20h 
temp1	equ 	20h	
temp2	equ 	21h	
count	equ	22h	
beep	equ	23h		
timer	equ 	24h 	;beeps after 1 minute to let you know it's on 

	; globals

GPIO		equ	05h

status		equ	03h
option_reg	equ 	81h
TRISIO		equ	85h

						; bits 
pin7	equ	0	;GP0  
pin6	equ	1	;GP1
pin5	equ	2	;GP2 and T0CkI
pin4	equ	3	;GP3 input only
pin3	equ	4	;GP4 
pin2	equ	5	;GP5 

z	equ	2	;zero flag

rp0	equ	5	;bit 5 of the status register

Start	org	0x00	;program starts at location 000
	goto	SetUp
	nop		;NOPs to get past reset vector address
	org	4
	goto	isr			

SetUp	movlw   07h      ;Set up W to turn off Comparator ports
	movwf   CMCON    ;must be placed in bank 0   
	goto 	Main	;Main

_25uS	movlw	.7
	movwf	temp1
	decfsz	temp1,1			 
	goto 	$-1	 	
	retlw	00
_130uS	movlw	.45
	movwf	temp1
	decfsz	temp1,1			 
	goto 	$-1	 	
	retlw	00		
_250uS	movlw	.84
	movwf	temp1
	decfsz	temp1,1			 
	goto 	$-1	 	
	retlw	00	
_100mS	movlw	.100
	movwf	temp2
	decfsz 	temp1,1
	goto 	$-2
	decfsz 	temp2,1
	goto 	$-4	
	retlw 	00	
_250mS	movlw	0FFh
	movwf	temp2
	decfsz 	temp1,1
	goto 	$-2
	decfsz 	temp2,1
	goto 	$-4	
	retlw 	00	
	;interrupt service routine		

isr	nop
	decfsz	timer,1		;creates 1 min delay to let you know it is on.
	goto	Main1
	movlw	03
	movwf	count
	goto	sss 		
Main	bsf	status,rp0 	;Bank 1			
	movlw	b'00100100'	;Set GP2 input  GP5 input
	movwf	TRISIO			
	movlw	b'10010100'
	movwf	OPTION_REG	; x000 0000 x=1= weak pull-ups disabled 
				; 0x00 0000 INTDEG Don't care
				; 00x0 0000  x=0 = internal instruction clock
				; 000x 0000 Count on falling edge - don't care
				; 0000 x000 0=prescaler assigned to timer0  
				; 0000 0xxx = 111 = 1:128  x100=1:32	
	bcf	status,rp0	;bank 0 		
	bcf	GPIO,4
	call	_100mS		;(settling time)		
	movlw	b'10100000'	;b'10100000'
	movwf 	INTCON		;,0  1=GP0,5 interrupt flag
				;,1  1=GP2 interrupt occurred
		;bcf	INTCON,2	;1=TMR0 overflowed. Clear overflow flag
		;bcf	INTCON,3	;1=enable GPIO port change interrupt
		;bcf	INTCON,4	;1=enable GP2 external interrupt
		;bsf	INTCON,5	;1=enable TMR0 overflow (interrupt)
		;bcf	INTCON,6	;1=enable all peripheral interrupts
		;bsf	INTCON,7	;1=enable all unmasked interrupts
	bcf	INTCON,5	;0=disables TMR0 interrupt
	bsf	INTCON,6	;1=enable all peripheral interrupts
	movlw	b'00010101'	;b'00110001'			
	movwf	T1CON		;,7  not used
				;,6 0=Timer1 is ON
				;,5,4  11=8 prescale (max) 01=1:2
				;,3 bit ignored
				;,2 This MUST BE SET!!!!!!
				;,1 0=int clock 
				;,0 1=enable timer 	
	bsf	status,rp0 	;Bank 1				
	bsf	PIE1,0		;,0 1=enables TMR1 interrupt		
	bcf	status,rp0	;bank 0 
	bcf	PIR1,0		;clear TMR1 overflow flag
	clrf	TMR1L		;clear the Timer1 low register
	clrf	TMR1H		;clear the Timer1 high register
	clrf	count		;count the number of cycles
				;Timer0 is not used 		
				; will go to isr when overflow occurs in TMR1
				;0.13 sec when prescaler=1:2  131,072uS	
				;input is LOW when no audio detected.	
aa	call	_25uS					
	btfss	GPIO,2		;Is input HIGH?  Start with a HIGH
	goto	aa						
bb	call	_250uS
	btfss	GPIO,2		;Is input LOW?   
	goto	cc
	goto	aa		;freq too low			
cc	call	_250uS
	btfsc	GPIO,2		;Is input LOW?
	goto	dd		
	goto	aa		;freq too low

dd	incf	count,1
	goto	bb

Main1	bcf	PIE1,0		;,0 0=disables TMR1 interrupt
	bcf	T1CON,0		;disable timer1
	bsf	status,rp0 	;Bank 1	
	bCf	INTCON,7	;disable all unmasked interrupts	
	bcf	INTCON,5	;disables TMR0 interrupt		
	bcf	status,rp0	;bank 0 		
	swapf	count,1
	rrf	count,1		;
	rrf	count,1		;only use top 2 bits
	movlw	b'00000011'
	andwf	count,1		;max 4 beeps			
	movf	count,1
	btfsc	status,z	;z flag will be SET if file is zero
	goto	Main
sss	bsf	status,rp0 	;Bank 1	
	movlw	b'00000100'	;Set GP4,5 output
	movwf	TRISIO	
	bcf	status,rp0	;bank 0 		
	call	_250mS
	movlw	0FFh
	movwf	beep		 		
	bsf	GPIO,4
	bcf	GPIO,5
	call	_130uS
	bcf	GPIO,4
	bsf	GPIO,5
	call	_130uS
	decfsz	beep,1
	goto	$-7
	decfsz	count,1
	goto	$-12		
	call	_250mS
	call	_250mS
	call	_250mS
	call	_250mS		
	goto	Main				


We have not produced the "Ultimate Key Finder" project. We have left some improvements for you to work on.
The detection software could be improved, the beep could be changed and the 1-minute alert could be lengthened. These are all things for you to try.
I don't think you will be able to turn the project into voice recognition but you will certainly be able to produce different tones or even a set of notes to indicate when a whistle is detected.
It's now up to you.

Parts List

Cost: au
$10.00 plus postage
Kits are available

1   -  4k7   SM resistor
2  -  68k    SM resistors
2  -  2M2   SM resistors

2  -  100n SM capacitors

2  -  BC 847 SM transistors (1F)

1  -  SPDT mini slide switch
1  -  22mm piezo diaphragm

20cm fine enamelled wire
30cm  - very fine solder 
1  -  8 pin IC socket 
5  - machine pins
1  -  PIC12F629 chip (with Whistle routine)
1  -  coin-cell holder
3  -  button cells
1  -  Prototype PC board