Trouble reading frequency

alexb2

Hello, I've used stamps many times over the years and this is the first time posting on this forum. BTW I have searched this forum and the net for an answer before coming here and still cannot find what I am looking for.

I am having trouble reading frequencies with my bs2 using piezo film sensor that I purchased from Parallax. I used the same schematics listed in the pdf. http://www.parallax.com/Store/Sensors/PressureFlexRPM/tabid/177/CategoryID/52/List/0/Level/a/ProductID/89/Default.aspx?SortField=ProductName,ProductName

My problem is that it will only show a frequency in debug window when I shake the sensor or by moving/bending it. It will not register anything if I put a loud radio speaker near it and not when I slam my hand on the table. I have to really hit the table hard near the breadboard to get it to show anything.

Am I using the wrong sensor for the task? I basically want to measure small vibrations or sounds of multiple frequencies (one would be from a cars exhaust).

Here's the basic set up.

Same schematics listed in the pdf from above page.
sample code.


v0 VAR Word
v1 VAR Word
v VAR Word
F VAR Word

MAIN:
PULSIN 5, 1, v1
PULSIN 5, 0, v0

v = (v0 + v1)*2

f = (50000/v)*20

DEBUG DEC f, " Hz "
DEBUG DEC v, " V ", CR ' just to show small numbers

P.S. I have also tried using 'COUNT' instead of 'PULSIN'.

Thank you,

metron9

"My problem is that it will only show a frequency in debug window when I shake the sensor or by moving/bending it."

That is not a problem, that is what this sensor is designed for. moving and bending is the only way it can produce a voltage.

If you want to pick up sound from a piezo you need something like this http://parts.digikey.com/1/parts/33-buzzer-piezo-4-1khz-ext-drive-cep-1110.html

Or a standard transistor radio earphone also works as a microphone!

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Post Edited (metron9) : 1/28/2009 7:08:46 PM GMT

alexb2

Okay, thanks, I will use a speaker for the sound part and play a little more with the vibration part (I figured holding it in between my fingers would show some sort of freg but doesn't).

Jonathan

Another thing is for small vibrations, you might want to add an amplifier, like with an op-amp. Same apllies with a speaker. Remeber that the pulse has to go above ~ 1.7VDC to register as a "high".

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alexb2

Remeber that the pulse has to go above ~ 1.7VDC to register as a said...
igh".

That is one stupid thing that I did overlook.
Thank you,