Specs for Murata piezo-speaker

[Arild P.]

I'm trying to create an audio line-output from a Texas instruments
"Speak & Spell compact" (educational talking toy) from the 80s which
uses a piezo-speaker.

The piezo device is no longer available, and Murata (the manufacturer)
can't supply me with the specs (which I need in order to create that
line-output, replacing the speaker).
The component name is: VSB41D25-07AR

It looks similar to this:
http://www.mcld.co.uk/oddmu/tincanbass/piezotransducer.jpg

Does anyone know the specifications (capacitance, resistance etc.) of
it?

 

[mc]

Try putting a 1k resistor in place of it, and see what you get. It won't
cause any harm.

 

[Arild P.]

Try putting a 1k resistor in place of it, and see what you get. It won't
cause any harm.

I'll give it a go, but regarding the specs I became aware of
capacitance playing a major role in such a component. So with the aid
of my digital multimeter I measures 133 nF across the piezo speaker.

When it comes to resistance across it there's something strange going
on which I can't explain.
The piezo speaker has two wires soldered to it (red and black, which I
assume means that it has a +/- polarity). If I measure the resistance
the "wrong" way round (e.g. the + probe of the multimeter to the black
wire and the - probe to the red wire) no value is displayed in any
range.
However, if I measure the resistance the other way round I get a
reading, but .... this is odd. I have to have the range of the
multimeter set to 40 MOhms, and the reading quickly fluctuates
-something like: 1, 2, 5, 19, 22 MOhms until I get an "OL" (overload)
meaning the range is exceeded.

So what does this mean?
Specs for this component would really help

 

[mc]

What you are observing, I think, is that it has some internal capacitance
and is holding a charge for a brief time.

But I think you will find that it is driven with a pulsating DC voltage
which you can feed to an audio amplifier. Its capacitance is not important
for operation.

Maybe, instead of a 1k resistor, use a 10k resistor.

 

[Franc Zabkar]

I'm trying to create an audio line-output from a Texas instruments
"Speak & Spell compact" (educational talking toy) from the 80s which
uses a piezo-speaker.

The piezo device is no longer available, and Murata (the manufacturer)
can't supply me with the specs (which I need in order to create that
line-output, replacing the speaker).
The component name is: VSB41D25-07AR

It looks similar to this:
http://www.mcld.co.uk/oddmu/tincanbass/piezotransducer.jpg

Does anyone know the specifications (capacitance, resistance etc.) of
it?

See http://www.thedigitalshop.net/techdocs/piezo.pdf

Refer to Fig 70.3 for an equivalent circuit, and page 15 for the specs
of your speaker.

- Franc Zabkar

 

[Eeyore]

I'll give it a go, but regarding the specs I became aware of
capacitance playing a major role in such a component. So with the aid
of my digital multimeter I measures 133 nF across the piezo speaker.

Sounds plausible.

When it comes to resistance across it there's something strange going
on which I can't explain.
The piezo speaker has two wires soldered to it (red and black, which I
assume means that it has a +/- polarity)

No it hasn't.

. If I measure the resistance
the "wrong" way round (e.g. the + probe of the multimeter to the black
wire and the - probe to the red wire) no value is displayed in any
range.
However, if I measure the resistance the other way round I get a
reading, but .... this is odd. I have to have the range of the
multimeter set to 40 MOhms, and the reading quickly fluctuates
-something like: 1, 2, 5, 19, 22 MOhms until I get an "OL" (overload)
meaning the range is exceeded.

So what does this mean?

It means you're discharging the capcitamce via the meter and charging it up
again with the reverse polarity you just put there when measuring the other way
round. Try doing the same with a 100n cap.

Specs for this component would really help

It has capacitance ( as dio all piezos ). Seems like 133n in fact.

Graham

 

[Arild P.]

On 23 Jun 2006 03:45:37 -0700, "Arild P." <[email protected]> put
finger to keyboard and composed:

See http://www.thedigitalshop.net/techdocs/piezo.pdf

Thanks! Much appreciated.

Refer to Fig 70.3 for an equivalent circuit, and page 15 for the specs
of your speaker.

Interesting! So if I make that circuit then connect it across the two
places where the speaker should go, the toy should act as if the
speaker is still connected, and I can then connect it to an amplifier,
my computer for recording or whatever?
In other words, I should do it like this:


speaker-out Line-out
from
toy
--------->-------------------------------->
| |
----- |
----- C1 |
| |
o |
o L1 -----
o ----- C0
| |
x |
x R1 |
| |
--------->---------------------------------->

(I hope that comes out right -I'm having trouble getting a fixed font
to display it).
If the above is the way to go, which values should the components have?
I don't have too much knowledge in the theoretical area of electronics,
so although I've read the documentation in that PDF document I couldn't
quite understand why there aren't any specific values, or at least
values directly related to the specs of the piezo element.
I don't understand what the talk about "resonant frequency" is either.
Isn't it enough to know the specs of the piezo speaker to build this
circuit, or are there other things I need to find out about the circuit
of the toy itself?