PIC sinking voltages higher that Vdd???

[manumenzella]

Hey. Sorry to bother you again.
I have just looked in Electrical Characteristics, but i cant seem to find my answer I think it might be the thing called "clamp current" or sth. but im not sure. I tried looking it up by Google without any luck, too.
Can you please tell me the parameter i should be looking for please???
Thanks in advance!!!!!!!!
Manuel

[Darrel Taylor]

Manuel,

All you need is a general purpose NPN transistor, and a 10k resistor.

10k from pic pin to the base, emitter to vss, collector to piezo, other side of piezo to +9V.

Setting the pin HIGH, will turn on the buzzer.

HTH,

[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.

[skimask]

Hey. Sorry to bother you again.
I have just looked in Electrical Characteristics, but i cant seem to find my answer I think it might be the thing called "clamp current" or sth. but im not sure. I tried looking it up by Google without any luck, too.
Can you please tell me the parameter i should be looking for please???
Thanks in advance!!!!!!!!
Manuel

1st page of that section, on the datasheets I've looked at so far, it's usually the 3rd parameter.

[malc-c]

Typing something like "driving piezo buzzer from pic micro" into Yahoo returned some interesting hits.

http://www.talkingelectronics.com/Pay/PIC/P6extra.html

I wouldn't expect the Piezo to draw much current, so a single transistor as DT suggested would be fine. If you want to drive things like motors then you could used an H-bridge or a Darlington power transistor.



For your Piezo you could omitt the 18R resistor and output transistor, and connect the buffer transistor's emmiter to the 12v (or 9v in your case) supply

More info can be found at http://www.talkingelectronics.com/Pa...PIC-Page3.html which explains the reason for using two or more transistors for high current loads.

Hope this helps