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:
Does anyone know the specifications (capacitance, resistance etc.) of it?
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
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, >> Try putting a 1k resistor in place of it, and see what you get. It won't
On 23 Jun 2006 03:45:37 -0700, "Arild P." put finger to keyboard and composed:
See
Refer to Fig 70.3 for an equivalent circuit, and page 15 for the specs of your speaker.
- Franc Zabkar
-- Please remove one 'i' from my address when replying by email.
Sounds plausible.
No it hasn't.
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.
It has capacitance ( as dio all piezos ). Seems like 133n in fact.
Graham
Thanks! Much appreciated.
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?
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