[Q] piezo transducer as "Beep" Generator / Receiver

[infantilo]

HI,
i've just an noob question about an piezo transducer.

I'd like to generate an 85dB "beep" with an piezo transducer; how pratical would it be to use the same piezo (on another arduino) to detect this beep?
(more detailed: one arduino generates the beep -> microphone -> loudspeaker -> another arduino should listen to beep)

The reason for asking is, that i'd like to build only one device (twice) that can work as Generator and Receiver.

I've read about the Problems using an piezzo as mic, but in my case i thought it could possibly usefull, as i nedd to detect the time when the beep begins ans so i won't have to care about a too large frequenzy range that could disturbe?!
Many thanks for advice!
 

[raschemmel]

Your project is possible but not trivial. If you rely on sound pressure level alone to detect the piezo, it may not be effective. If you design a circuit to detect that particular frequency band it is a bit complex because you either need one of these or a notch-pass filter that blocks all frequency bands except on. This is actually , the concept of how this works is simple if you look at the frequency response for a low pass (LP) filter and a high pass (HP) filter.

If you combine both LP & HP, there are two possibilities:
A- f_cutoffHP > f_cutoffLP  (called a Notch Filter)

Frequency response looks like this:
-----|        |-------
        |___|
and
B-  f_cutoffHP < f_cutoffLP (Called a NotchPASS Filter)

Frequency Response looks like this :
              ____
               |        |
______|         |______

If you combine the sound detector with the NotchPass Filter (B), then the detector only detects sound in that band (the band that the piezo sound falls in. You have to know what the piezo sound frequency is in order to design the LP and HP filters and they can be single order, second order , 4th order etc
each offering greater filtering characteristics. Which type you choose depends on your application and I couldn't tell you which one would work for you. Generally , you use the lowest order you can get away with and still have it work the way you want. If a first order doesn't work in your application then you would escalate to 2nd order and so forth. This may be more than you bargained for. Newbies tend to underestimate just about everything in electronics and uP. That's why we're here.

[Henry_Best]

85dB is mighty loud. (Rock concert/pneumatic drill/jet engine loud)
Do you have a piezo capable of making that much noise?
If you have, I'm glad that you don't live near me.

[infantilo]

First many thanks for your replys! (and i'm really sorry for my terrible english writing)

85dB is mighty loud

I only ment i need to generate an fairly loud beep, so it can be recorded in nature (e.g. ski slope or empty stadion) the 85dB were just an example value (sorry for that) 

@raschemmel:
I now understand that i have to use an Bandpass/Notch filter to respond "only" to the desired frequenzy.
This rules for both, an mic and an simple piezo.
But do you think an piezo transduce in an housing, mounted would be cappable to do the job?
Or will i need to use both , an piezo for generating and a mic for receiving?
The receiver will stand between 1 and 2 meters away from the loudspeakers.
(I'd like to measure delta time between / lip sync /av alignment instead of using the good old movie clapperboard (for personal use only), i did this by coding android app, but this had to be calibrated for each phone manually before. Everything under 1 frame would be fine to measure)
Maybe the FreqCounter library or the Yin Algorithm could be used for?

Once more thanks for any reply and help! This is really appreciate your help!   

[MarkT]

85dB is mighty loud. (Rock concert/pneumatic drill/jet engine loud)
Do you have a piezo capable of making that much noise?
If you have, I'm glad that you don't live near me.

No it isnt.  You are confusing 85dB with 140dB.  http://www.gcaudio.com/resources/howtos/loudness.html

[raschemmel]

First- It's NOTCHPASS filter NOT NOTCH filter (which is the exact opposite)

Second- It's customary for the vendor to list the piezo frequency when advertising the buzzerr,
85 dB Piezo

If you pay attention to what you are reading you may catch such details.

There is an Android phone Audio Spectrum Analyzer App that could be used to measure the frequency.
Alternately, it MIGHT be possible to use a microphone preamp circuit to capture the audio signal to view on an oscilloscope.