PIC sinking voltages higher that Vdd???

[mister_e]

Manuel what kind of piezo do you talk about? Those 'plug and play' or those you MUST produce a tone to hear something?

For high current, Darlington can be nice in some case, but they usually switch slowly and many have a BIG voltage loss between Collector and Emitter (few volts or so). I prefer MOSFET.

[malc-c]

Good comment regarding the MOSFET's, some of which have a low enough gate current so they can be driven direct from the PIC

[mister_e]

Depending of the load and frequency (if there's any), yes.

For much demanding stuff, there's still the MOSFET driver solution. Tons of different models and type available. Microchip TC1427 are not too bad.

[manumenzella]

Hey. Thanks for all the answers. I think im going to connect a npn transistor as most of you suggested. The probem is that, as it is battery powered, i need to keep the current draw very small. Do you know which will be (more or less) the current flowing from the IO to the base of the npn???
I was going to use the multimeter to measure it, but, after the cleaning lady came home, the screen was broken into pieces!!!
Well, thanks again for your help
Manuel

[skimask]

Hey. Thanks for all the answers. I think im going to connect a npn transistor as most of you suggested. The probem is that, as it is battery powered, i need to keep the current draw very small. Do you know which will be (more or less) the current flowing from the IO to the base of the npn???
I was going to use the multimeter to measure it, but, after the cleaning lady came home, the screen was broken into pieces!!!
Well, thanks again for your help
Manuel

Using a transistor instead of a MOSFET is going to cost you a few mA in base current right there. MOSFET's have practically no gate current, generally in the pico-amps (except when switching states due to gate capacitance). Use an N channel MOSFET, 2N7000. It'll easily handle 12v across the drain-source, and switch on/off with 5v logic levels on the gate.

[sougata]

Hi,

Some PICs have an open drain output (say PORTA.4). This means that it has only the lower side N-Channel MOSFET inside. And according to a Microchip FAE this can tolerate upto 8 volts safely. Hopefully it should not be a problem with your buzzer and 9v battery.

[Darrel Taylor]

And according to a Microchip FAE this can tolerate upto 8 volts safely.

You're right, it does say that. But it also says that PORTA.4 has protection diodes to VDD and VSS.

Which one are we supposed to believe?

I suppose a little testing would tell.
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