On 10/18/05, Kevin <kben@universal.dca.net> wrote:
> A friend has a circuit that turns a pin hi 4.5V to low 0.1V,
> current is about 10ma. He has a piezo speaker connected to
> the pin and to ground. So when he sets the pin high
> he wants the piezo speaker to buzz, and when he sets
> it low he wants it off. However, when it goes low it's not
> at 0V so their is a noticable hum from the piezo. What's the
> easiest way to keep the pin at OV, to keep the piezo from
> humming when it should be off.
>
> Thanks for any suggestions,
> Kevin
>

This sounds like a ground problem.

But, if you can't fix that:
 Figure out how much current it takes to make 0.1 go to 0.0V, and add
a resistor across the piezo.
or (assuming you are taling about a piezo with a built-in driver
circuit, not a bare disc):
 Figure out what AC component is making the piezo hum, and add a
capacitor across the piezo.

Regards.
Mark
markrages@gmail
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