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Protecting circuit from piezoelectric disc voltage spike

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I have a piezoelectric disc, and I’m trying to use to build a primitive sonar. I connected the disc to an oscilloscope and if I press very hard on the disc, I see that the voltage can spike pretty high. I’m not sure how much current there is.

In an application with a piezoelectric device, should I use a voltage regulator on the output of the piezo, and would that protect my circuit on the other side? I want to connect it to an ATTiny85 without frying the chip.voltage-regulatorattinypiezoattiny85shareedit  follow  flag asked 5 hours agomj_29922 silver badges77 bronze badges

  • 5No, you wouldn’t use a voltage regulator you’d use a series current limiting resistor. – Andy aka 5 hours ago
  • 1If you want to transmit a SONAR pulse to get the piezo to ring strong, you want to have a HV transistor to drive it high then open and ring then clamp shut to 0V to discharge the energy fast (blanking) pulse then the Rx echos can be measured except for the tbd xxx ns or us delay time to stop transmitting the ringing pulse. So adding a series resistor makes that less sensitive for the transmission pulse. otherwise a step up pulse transformer can be attempted for Tx with a high side PNP current source then an NPN clamp clamp to gnd with a small deadtime using a half bridge BJT driver. – Tony Stewart Sunnyskyguy EE75 4 hours ago 
  • 1If you define your design specs in good detail and any component spec links, then a good answer is possible – Tony Stewart Sunnyskyguy EE75 4 hours ago 
  • @mj_, the usual quick and dirty trick is to use a zener diode. But I found that zener is not very effective. – tlfong01 2 hours ago   
  • You might like to read my measurement of piezo spike with and without the protective zener: “Piezo sensor to pick up acoustic instrument signal using Rpi and ADC Asked 1 year ago Active 1 year ago Viewed 569 times”: raspberrypi.stackexchange.com/questions/103868/…. Cheers. – tlfong01 2 hours ago   

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2 Answers

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Question

Protecting circuit from piezoelectric disc voltage spike


Answer

The voltage spike might be as high as 30V. You can use a zener to clamp the spike. See appendices for more details.


References

(1) tlfong01’s piezo experiment, Rpi SE 2019

(2) Piezo Pickup Transducer 27mm Contact Microphone Trigger – Discs Elements for Acoustic Instrument: Guitar, Drum, CBG etc. with Leads $6.99/12Pcs

(3) MCP3008 SPI 8 Channel 10 Bit ADC Datasheet – MicroChip

(4) How to Build a Piezo Knock Sensor Circuit – Learning About Electronics 2013

(5) Piezo knock sensor circuit- Demo – Youtube 2013


Appendices

Appendix A – Characteristics of piezo used in this experiment

Piezo Pickup Transducer 27mm Contact Microphone Trigger – Discs Elements for Acoustic Instrument: Guitar, Drum, CBG etc. with Leads $6.99/12Pcs

Resonant frequency: ***4.6 +/- 0.5 KHz***

Resonant impedance (ohms): ***300Ω max***

Plate material: Brass

For: Acoustic Instrument Pickups, Stomp Boxes, Contact Mics, etc...


Appendix B – Piezo toy schematic

Errata and apology

My previous schematic has a typo error. The parallel resistor should read 1MΩ. Many thanks to @tomnexus for point out my silly mistake.


piezo cct

Appendix C – Voltage spike without Zener protection


zener protection

Appendix D – Detecting (Electromagnetic Buzzer) flyback voltage and current spike experiment


Detecting (Buzzer) flyback voltage and current spike experiment 1/2


Detecting (Buzzer) flyback voltage and current spike experiment 2/2


buzzer voltage spike

Appendix E – Buzzer Back EMF 30Vpp 100 ns Spike Wavelet Selfie

The voltage spike can be as scary high as 30Vpp, But the duration is small 100nS. If the human finger lightly taps/knocks the piezo disc, the mechanical energy transferred to the piezo disk should be of the same order of the 5V electromagnetic buzzer’s little hammer hitting the bouncing steel spring bar. It is tedious to use my scope’s one shot trigger to display my tapping of the disc. So I used the buzzer to display the repeatedly back EMF voltage spike. I did use my scope to zoom in the spike and found her a pretty little wavlet, so I took a selfie picture for her.

Warning to the OP:

(1) But if you are using a big hammer to hit a big disc which is part of a percussion musical instrument, then the spike might be as ridiculous high as 1000+ volts! and for pretty sure fry your ATTiny85.

(2) Me only a friendly electronics hobbyist. No guarantee no nothing won’t melt down or blow up, or electrocute a cat.

back emf selfie

shareeditdeleteflagedited 26 mins agoanswered 2 hours agotlfong011,18911 gold badge44 silver badges77 bronze badges

  • 1Could you please, please try to post straightforward answers that simply make your point without all this division into less relevant appendicies and links? – Chris Stratton 1 hour ago 
  • 2Uh, mΩ≠MΩmΩ≠MΩ – tomnexus 1 hour ago 
  • @tomnexus, Many thank for pointing out my silly mistake. My apologies for any confusion caused. Cheers. – tlfong01 1 hour ago   

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Please post a circuit when asking questions. A parallel resistor with a proper value is what you need. The current isn’t high. The first circuit is with Arduino. The second circuit is recommended.

enter image description here

The circuit shows a 1MR resistor.

More complex option:

enter image description here

And the best way, but you have to reduce the voltage to 5V or 3.3V, depending on your MCU. 

You can always use a standard sonar sensor, but they are expensive.

Sources: http://www.learningaboutelectronics.com/Articles/Piezo-knock-sensor-circuit.php http://www.robotoid.com/appnotes/sensors-piezo-disc-touch-bar.html https://www.homemade-circuits.com/simplest-piezo-driver-circuit-explained/ https://www.homemade-circuits.com/diy-contact-mic-circuit/shareedit  follow  flagedited 56 mins agoanswered 4 hours agoCFCBazar com44811 silver badge88 bronze badges

  • 1Parallel? No. Questions on Stack Exchange sites must have stand-alone value, they cannot rely on links for the entirety of any accurate content. – Chris Stratton 2 hours ago

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