3

I am using Falstad's circuit simulator to test a design of an Op-Amp based microphone-speaker system...kind of like a megaphone, but the speaker is going to be a piezo plate. Falstad does not have a speaker or piezo speaker component I can add. What resistor/capacitor/diode/inductor/etc. would properly simulate a piezo in the circuit?

Current circuit diagram for reference. The top right box is bandpass filter. Circuit diagram

traisjames
  • 199
  • 1
  • 11

2 Answers2

1

Sure you just have to know the RLC values and add a current limit to the OpAmp with a series Rout, inside the feedback loop for Isc = V+,-/Rout

enter image description here

If you choose to measure these values, sweep the piezo with a series R that attenuates roughly in half, then use a cap that does the same then plug these values and big values for L (mH) and match the Bode plot using Falstad http://www.falstad.com/circuit/e-filt-hipass-af.html

Tony Stewart EE75
  • 1
  • 3
  • 54
  • 182
  • Piezo electric tweeters for audio have a capacitance of 150nF. Some cheap amplifiers will become unstable with that much capacitive load. –  Apr 12 '18 at 04:25
  • What is Cop and Cos in your image? – traisjames Apr 12 '18 at 23:31
  • C {parallel and series} . All Xtal, ceramic, MEMS and piezo resonators have two (high Q) resonant frequencies close to each other. You can use either way and when done right with a high series R or better with current source ( collector out ) or tiny stepup transformer get voltage amplification in parallel mode and in series get current amplification with low impedance driver. – Tony Stewart EE75 Apr 13 '18 at 01:52
  • I suggest you do some reading before you commit to a design https://pdfs.semanticscholar.org/6cb8/30411d522dc503b251c73f193ef079650929.pdf Also Murata has useful info and Google https://www.google.com/search?q=piezoelectric+buzzer+impedance&num=30&client=firefox-b-ab&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjBw86IlbbaAhVH7IMKHfJjCEgQsAQITA&biw=1176&bih=903 – Tony Stewart EE75 Apr 13 '18 at 02:11
1

Piezo transduces have horribly (I'd say non linear) frequency responses; Tony Stewart answer is a good approximation (model) if you are running it near its resonance frequency. It all depends the reason for your simulation.

At a zero order approximation a piezo transducer is… a capacitor. The value is usually stated as C0 or base capacity; you could use some megaohm in parallel if the simulator chokes (I don't know Falstaff but SPICE happily converges with that). If you have a definite 'nominal' impedance you could use that.

An initial approximation adding an RLC tank covers the main resonance point and is mostly useful for single-tone circuits (like beepers).

The 'read' model would be something like an infinite series of RLC in parallel, each of these covering one oscillation mode of the piezo material. It's difficult to get these from the manufacturer, you'll need to do an impedence sweep and synthesize the 'major' resonances in your area of interest.

Do you have at least the frequency response of the transducer? If it's reasonably flat the RC model would be enough.

Lorenzo Marcantonio
  • 8,231
  • 7
  • 28