Alt-BEAM Archive
Message #10070
To: beam@sgiblab.sgi.com
From: "Sathe Dilip" sathe_dilip@bah.com
Date: Fri, 11 Feb 2000 12:41:37 -0500
Subject: [alt-beam] Re: condenser mics
They should work fine with amplification. Electret microphones need
bias & amplification to be useful. The bias is required because usually
the can also includes a FET. If you are using it in a low voltage
circuit (say 1.5 to 3 volts), use a two transistor amplifier (I am not
sure how much gain you need). If using in a higher voltage circuit (5V
& above), you can use an Opamp. You should be able to find suitable
circuits in many places. Look for circuit archives on the web.
An ohm meter won't help you because 1) Electret element is like a
capacitor (very low value - in pFs) but with permanently polarized
plates. You could say electret is the electrostatic equivalent of a
magnet. and 2) because you are most likely looking at the drain &
source ends of a FET anyway - the actual electret element being
internally connected between the source & the gate with a biasing
resistor to the drain.
To make them directional, you will have to mount the mic inside a tube
or something.
Hope this helps
Dilip
Kelly Petriew wrote:
>
> Are tiny condenser mics (found in computer microphones) good enough to
> use? Would they be sensitive enough? I haven't actually checked to
> resistance of one yet (I don't have a good ohmmeter at work)..
>
> Thanks in advance
>
> --
> Kelly Petriew
>
> Systems Support Analyst
> The StarPhoenix
> 204 5th Avenue North
> Saskatoon, Saskatchewan
> Canada
> S7K 2P1
> 306-664-8250 extension 569
--
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The early bird may get the worm, but the second mouse gets the cheese.
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10071 Fri, 11 Feb 2000 10:40:02 -0800 (PST) [alt-beam] Re: ...yes, two more new questions..... "BEAM Mailing List (E-mail)" "J. Parks" From Bothell, eh? Hey, I'm right down the street in Kirkland!
Anyhoo, increasing the voltage source to the capacitor does not change the
maximum charging time of the capacitor. It will charge up more quickly,
but since the charge rate is proportional to the voltage source, time
won't decrease.
The time to charge up to some constant threshold voltage (like for
switching a diode), _will_ decrease, because the cap charging rate is
faster with higher source voltages. If you want to increase the voltage
source, and also maintiain the same diode switching time, then you have to
increase the capacitance.
However, you increase capacitance by combining them in parallel. Capacitance
DECREASES if you add them in series. It's the opposite of the resistor
convention.
-Jake
On Fri, 11 Feb 2000, Scolman,Jim wrote:
> Good morning, assuming a functioning circuit, if I increase the size of the
> solar cell, to I use Ohms Law to keep the circuit in balance, i.e.,
> functioning? Would connecting, say three caps of n value, in series have
> better performance than one cap of 3n value? .......I'm very sure no one
> has thought of these ideas before..........Thanks......JWS.
>
> Jim Scolman
> AMS Services, Inc.
> Bothell, WA
> 425-402-1000 x353
> 206-910-6095
> scolmaji@amsworld.com
> Network Administrator
>
>
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