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'[EE] Driving piezo buzzers'
2005\11\17@213402 by Padu

face picon face
Probably this is a dumb question, but hey, I'm a specialist at dumb questions.

In a circuit I'm designing, I want to sound an audible alarm when a certain temp threshold is achieved. I'm going to control this alarm using a PIC. I want to be able to hear that alarm at a certain distance (20-30 meters for example), therefore it must make a good sound.

I was looking at some buzzers capable of producing 100dBA at 10cm, but they are rated at 12VDC. Their power consumption is low (8mA) therefore it is feasible to drive it directly from a PIC pin, but at only 5VDC I don't know if it will be loud enough. To speak truly, I don't even know what happens if I plug it to a 5VDC source. I'm guessing it will have a lower volume.

I think my main question is this: Do I really need to go the extra mile and chime in an NPN transistor to drive the buzzer? (I do have a 12V power rail on my circuit).

Right now I'm thinking about doing it (I mean installing the transistor). I've selected a MMBT123S-7 from diodes inc with a 2.2K between the pic pin and the transistor base. Is it a good selection?

Cheers

Padu

2005\11\17@222747 by Jinx

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> Probably this is a dumb question, but hey, I'm a specialist at
> dumb questions

Practise makes perfect. Just hold on to that dream of being
the best darned dumb question asker you can be ;-)

Higher voltage will produce more volume. To be audible at
20-30m I'd definitely use the 12V rail. Inside the buzzer will
probably be a DC-AC voltage multiplier (12VDC to 28-
30VAC maybe). If you wanted to get a little extra, use a FET
rather than a bipolar to switch the 12V

2005\11\18@073822 by olin piclist

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Padu wrote:
> I think my main question is this: Do I really need to go the extra mile
> and chime in an NPN transistor to drive the buzzer? (I do have a 12V
> power rail on my circuit).

Doesn't the buzzer cost 10x to 30x more than the transistor and resistor?
So let's see, for $2.00 it is out of spec and likely won't work, and for
$2.05 it is guaranteed to work.  Gee, I don't know, that's a tough call.


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2005\11\18@123509 by Padu

picon face
"Olin Lathrop"
> Padu wrote:
>> I think my main question is this: Do I really need to go the extra mile
>> and chime in an NPN transistor to drive the buzzer? (I do have a 12V
>> power rail on my circuit).
>
> Doesn't the buzzer cost 10x to 30x more than the transistor and resistor?
> So let's see, for $2.00 it is out of spec and likely won't work, and for
> $2.05 it is guaranteed to work.  Gee, I don't know, that's a tough call.


Yes, that makes perfect sense. The thing is that I had never used a buzzer
in my huge circuit design experience (this is the second one 8^D), and I
know I have a tendency to overcomplicate things...

2005\11\20@071053 by Steph Smith

flavicon
face
piezo buzzers come in two types,those WITH driver circuits built-in,and bare
buzzers,the driver type only need a power supply to make a (VERY) loud
noise,the bare ones must provide a square wave (ideally) pulse train at
supply voltage,so the supply available makes a big difference,my suggestion
is 'suck it and see';try it with what you have,this statement counts for all
experimental electronics.Some things work great,some things need
'adjustments',and some things (if you get the maths wrong) go BANG!.at least
you dont have to wait for slooow post to try an idea!enjoy experimenting at
120dB but try not to do it at 3in the morning ;^<
{Original Message removed}

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