# very basic doorbell

Discussion in 'Electronic Design' started by [email protected], Sep 24, 2007.

1. ### Guest

Hi all,
I'm designing a very simple doorbell circuit. I am very new to
electronics, so I'd really like to verify my idea with someone.
I'll get a 10mA, 12 volt piezo buzzer from Radio Shack and plan on
running a 12 volt battery in series with a 1200 ohm resistor to the
buzzer from a push button.
I'm using 1200 ohm resistor based on R = V / I, that is 12
volts / .01 amps = 1200 ohms.
I have a paranoia about starting a fire -- under what conditions,
if any, could a circuit like this start a fire?
Thanks so much if anyone wants to indulge in such an elementary
post....

2. ### Jan PanteltjeGuest

That likely means it uses 10mA when it is connected to 12 V.
You do not need and do not want the resistor.
The thing itself is about 1200Ohm

and plan on
A battery with enough Ah and a low enough Ri together with a short in the
buzzer *could* do it.
If you are paranoid use a 50mA fuse in series.

3. ### Guest

thanks for the response. I just realized I should have posted in

4. ### Tam/WB2TTGuest

What you calculated is the total resistance; that is the value of the
external resistor, plus the resistance of the buzzer As somebody poined out,
the buzzer is probably about 1200 Ohms by itself. That would be how they got
the 10 ma.

Tam

5. ### Guest

cool - got it.
One more question, how is a 50mA fuse determined? That is, why a 50mA,
not 40, etc.

thanks a lot...

6. ### Peter BennettGuest

The fuse value is not particularly critical - you want it large enough
that the fuse will not blow during normal operation, but small enough
that a true fault will blow it. You also want a
commercially-available value, which may be why 50 mA was suggested,
rather than 40 mA.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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7. ### neon

1,325
0
Oct 21, 2006
POWER is the key 12v and 50ma is nothing. the transformer will open up with a short and that is the wost case scenario.

8. ### Rich GriseGuest

Apology accepted.

Everybody makes mistakes - that's how we learn stuff.

Cheers!
Rich