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From: firstname.lastname@example.org (carltons)
Subject: Re: Loudspeaker and microcontroller
References: <email@example.com> <3DB65042.66FB6FCB@scazon.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Wed, 23 Oct 2002 10:43:13 GMT
Date: Wed, 23 Oct 2002 10:43:13 GMT
firstname.lastname@example.org (carltons) wrote:
> In article <3DB65042.66FB6FCB@scazon.com>, Paul Burke wrote:
> > jools wrote:
> > >
> > > Hi
> > >
> > > Im trying to create a door sensor and door bell configuration using a
> > > PIC and loudspeaker.
> > >
> > > The problem is making the sound loud enough to hear, a peizo is not
> > > really loud enough to hear so a small speaker is going to be used. The
> > > problem is can I drive is directly from the uC pin? Or does it require
> > > more current than this can supply?
> > >
> > Just a FET buffer (see thread on output buffers - I used a BSS138) with
> > a 100k pulldown on the gate (not strictly de rigeur), and a 50-75 ohm
> > coil speaker up to the power supply (don't forget parallel diode). I did
> > this recently for fun, quite enough noise for a doorbell.
> > Paul Burke
> Questions should be how much sound do you need? Speaker impedance is
> meaningless when it comes to how "loud" a speaker is. Different speakers
> have different efficiencies. If you look around you can probably find a
> 16 ohm 40mm diameter speaker which can be driven with a bridge audio
> amplifier using a power supply of 7.5vdc or so at some fairly low power
> levels (~ 500 mW) which should give you about 90 dbSPL. If the signal is
> a tone or a sort of tone, this will definitely get your attention. There
> are three important parameters here, speaker efficiency, speaker
> impedance, and supply voltage. You have to drive the speaker to the power
> level necessary to get the sound level you need.
> Steve WB4CZR
Follow up to my above message. If all you want is a big buzzing noise to
get your attention then many of the piezo's will give you this. I would
caution, however, if this is going to be a door bell, that you should
consider whether you want this to be buzz or something more pleasing to
the ear. For example, you are working on your computer or doing some
other task and all of a sudden you get this annoying sound in your ear.
Yes, you know its the doorbell and you need to answer, but think about the
mood it has now put you in, especially when you get to the door only to
find out it's some religious group come to give you "the word of God".
You could easily lose it and go off the deep end with very little nudging
in this condition. I would suggest a simple kind of tone which will get
your attention without annoying the hell out of you. Take it from a guy
that has gone to the door in his underwear with a hangover only to find
someone in a white starched shirt with a satchell and a pile of "Watch
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