How to connect Buzzer to PIC?

[dompower]

Dear Melanie,
You forum has lots of interesting informations. Thanks for keeping upto-date information.
I have a problem. I got a piezo buzzer from a smoke detecting alarm.
I like to use it in my PIC based circuit.
This buzzer has three wires. (red, black & white)
Can you suggest why there are three wires. I guess red for +, and blank for -.
Since this one is sealed I am unable to go thru.

Please help me.

DOminic
Riyadh
Saudi Arabia

[Melanie]

First make sure it's the Piezo you've got - and not the Sensor.

The three wire devices usually employ the third wire to change the tone. When connected to Vdd you'll get one tone, and when connected to 0v you get another. That's the way they get the 'warbling' effect for the Alarm sound.

Other more sophisticated Piezo's allow the sychronisation of several sounders - and they use the third wire for that purpose. You'll know that is the type if the original smoke alarm had an additional conector for connecting to additional alarms.

Experiment and see what you get...

[mtripoli]

First make sure it's the Piezo you've got - and not the Sensor.

The three wire devices usually employ the third wire to change the tone. When connected to Vdd you'll get one tone, and when connected to 0v you get another. That's the way they get the 'warbling' effect for the Alarm sound.

Other more sophisticated Piezo's allow the sychronisation of several sounders - and they use the third wire for that purpose. You'll know that is the type if the original smoke alarm had an additional conector for connecting to additional alarms.

Experiment and see what you get...

Maybe... I'm guessing it's a "self-drive" piezo buzzer. It needs a transistor and a few resistors to make it work...

[Michael Wakileh]

Every so often I find myself buying products just to find out how they work... Recently I bought a cheap battery powered Piezo alarm...very small and quite loud...
(I believe it's sweeping btw. two frequencies to be even more
audible...so it's probably a piezo transducer.)

I'm looking for help in figuring out how they made it so loud.

(The audio jack is being used as a switch...alarm goes on when
pin is pulled out...pin is stopped from coming out via housing...nice hack)

I will draw up a schematic soon... here some pics

Unfortunately I've never seen the critical part in question (black with 3 pins).
I'm guess I'm looking at a transformer? inductor?

Can anyone give me hints towards reading material or electrical tests I can do to find out more...

[ScaleRobotics]

Looks like the large 3 pin part might have heat shrink around it. Is that the case? If so, can you cut it off, and see a part #?

[Michael Wakileh]

Unfortunately no part number... just a bunch or really fine coils... I tried to be careful but I cut through them.... Perhaps I'll buy another unit so I can find out how many coils etc... but I guess we have an answer. I am not familiar with transformers. Logic tells me this one has a comon ground...input is boosted drive the piezo at higher voltage... I did a very brief search of farnell but didn't find anything similar... Anyone know part numbers or supliers of small 3 pin tranformers?

[mtripoli]

It's a coil (inductor) to generate flyback voltage. There's a switching circuit that creates a high voltage to apply across the piezo element. Piezo elements are generally designed to be run at high voltage; 30-200V is not uncommon. In a really good design the piezo will also be in a Helmholtz enclosure as well to really get everything from the system as a whole. Years ago I designed these things for car alarms. 120dB was on the low end of what you could achieve...

Do some searching on piezo elements; off the top of my head I'd say have a look at Murata. I seem to recall that they have some pretty good doc's on these things.

Mike Tripoli

P.S. I found the doc I was talking about pretty quickly: http://www.murata.com/catalog/p15e6.pdf. It's a good starting point...