Why this strange piezo-buz circuit?

F

flat5

Member

• Feb 24, 2009

• #1

What is the reason for doing the circuit this way?

 

Attachments

• piezo-buz 1.gif

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A

ataul

Member

• Feb 24, 2009

• #2

buzzer use as a simple feedback for oscillation.

 

F

flat5

Member

• Feb 24, 2009

• #3

That occurred to me but I thought the feedback was negative.

 

U

Ubergeek63

Well-Known Member

• Feb 24, 2009

• #4

flat5 said:

That occurred to me but I thought the feedback was negative.

Click to expand...

the piezo is a reactive element that introduces phase shift.

 

Hero999

Banned

• Feb 24, 2009

• #5

I can't see it working, not without something to bias the transistor on slightly.

 

Roff

Well-Known Member

• Feb 24, 2009

• #6

Hero999 said:

I can't see it working, not without something to bias the transistor on slightly.

Click to expand...

That's what I thought. Either the piezo element has a shunt resistive component, or bias current is provided through the jumper.

EDIT: Figure 9 in **broken link removed** from Murata has a similar circuit.

 

Last edited: Feb 24, 2009

F

flat5

Member

• Feb 25, 2009

• #7

The circuit was taken from the Proteus v7 samples.
Here is an excerpt from the Murata PDF.
Thanks Roff and et al

 

Attachments

• Self Drive piezoe buz 2.gif

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audioguru

Well-Known Member

Most Helpful Member

• Feb 25, 2009

• #8

Murata's schematic of the oscillator for a piezo beeper uses a piezo with a 3rd electrode, the feedback electrode. The feedback electrode is out-of-phase to the main electrode (it is a Hartley oscillator) so the transistor has positive feedback.
I think it automatically oscillates at the loudest frequency of the piezo/helmholtz cavity.