Oscilloscope help

[Megahertz]

This is neither an IR nor an RF signal. I put the scope directly to the uC pin outputting this signal. This is the waveform which creates an alarm like noise when fed to the base of the npn transistor on which a coil and a piezo buzzer are connected on the collector side in parallel to each other. But since the pulses are changing so quick, visually I can only make out that the minimum pulse is 150uS and MAX is 250uS. These pulses are increasing from 150 to 250 in some number of steps. I tried replicating this in equal 10 increments of 10uS but it does not match as it does not produce the same sound effect. So I logged the data, but need someone to explain me what the two long rows mean. To me it seems some values (between 150uS - 250uS) are repeated more than once, I am hoping the correct interpretation of the logged data will make it more clear.

[kellyseye]

Looks like 'swept' signal.

The square wave frequency is being increased (swept) from x(Hz) to y(Hz) by a modulating waveform. It 'looks' like it's sweeping from around 2kHz to 3kHz by a low (250Hz???) signal.

Configure an output to a 2kHz square wave and arrange for it to increase by 4Hz every 4uS until it reaches 3kHz then repeat.

[Megahertz]

Hello kellyseye, I tried the following, but no sucess:

while 1
		Pulsout PortC.0,25
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,24
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,23 
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,22
@	NOP
@	NOP
@	NOP
@	NOP		
		Pulsout PortC.0,20 
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,19
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,18 
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,17
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,16 
@	NOP
@	NOP
@	NOP
@	NOP
		Pulsout PortC.0,15
@	NOP
@	NOP
@	NOP
@	NOP

Wend

[Megahertz]

Here I have recorded the sound produced by the buzzer. Please rename the attachment to "Memo.m4a" from ".pdf" as I could not upload it in its original format.

[Darrel Taylor]

Try this ...
You'll need to put the piezo circuit on a CCP pin.

Freq  VAR WORD

Main:
    FOR Freq = 3000 TO 4000 STEP 10    
        HPWM 1, 127, Freq
        PAUSE 1 
    NEXT Freq
GOTO Main

It should sound something like this ... http://support.melabs.com/DT/Piezo.wma

[Megahertz]

Thanks Darrel, I will try it tomorrow with 16f877A which I have. But I would like to ask if this task can be made possible using a smaller PIC without an HPWM, I would like to use 16F676 if possible as it is very easily available and where I am and if this takes off then it will be economical as well.

In the mean time I am attaching the datasheet of the Chinese uC which is controlling the base of the NPN transistor connected to the piezo & coil. The signal comes out from PIN 2, which to me seems just an I/O pin.

Thanks

[Darrel Taylor]

Yes, of course it can.
It's only 3-4 khz. You can generate that in software easily.

But see if it drives your piezo first.
I was assumming your piezo has a resonant frequency of ~3.5khz.