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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 10:19:45 GMT
Date: Wed, 23 Oct 2002 10:19:45 GMT
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.
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