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Sci.Electronics.Basics -> removing condenser mic from a PDA and modifying circuit for line-in ?
There are 5 messages in this thread.
You are currently looking at messages 1 to 5.
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Author: Mad Scientist JrDate: 13:33 28-08-08
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I have an old PDA that I would like to modify (if possible) by taking
out the built in condenser mic and replacing it with a 1/8" or 1/4"
jack that I can plug another device into. Mainly I want to plug a
standard stereo headphone output (from iPod/cellphone/walkman/etc)
although it would be cool to be able to connect a line-level out from
a mixer, or directly plug a guitar in. The latter ones would probably
require a different circuit so for simplicity I'll just stick to the
first scenario (headphones out). Assuming I successfully can de-solder
and remove the condenser mic from my PDA and have two leads (which
went to the mic) free to solder my new input to, what kind of circuit
do I need to place between the new jack and the leads, so the input
works? The PDA must have some kind of preamp built in to drive the
condenser mic, so I am thinking maybe some kind of resistor or volume
control to "step down" the signal strength before it goes into the
PDA's preamp? I suspect the audio fidelity won't be the greatest, but
as long as it's passable I would like to try. Any info would be most
appreciated... thanks.
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Author: jwvmDate: 15:04 28-08-08
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On Aug 28, 1:33=A0pm, Mad Scientist Jr <mad.scientist...@gmail.com>
wrote:
> I have an old PDA that I would like to modify (if possible) by taking
> out the built in condenser mic and replacing it with a 1/8" or 1/4"
> jack that I can plug another device into. Mainly I want to plug a
> standard stereo headphone output (from iPod/cellphone/walkman/etc)
> although it would be cool to be able to connect a line-level out from
> a mixer, or directly plug a guitar in. The latter ones would probably
> require a different circuit so for simplicity I'll just stick to the
> first scenario (headphones out). Assuming I successfully can de-solder
> and remove the condenser mic from my PDA and have two leads (which
> went to the mic) free to solder my new input to, what kind of circuit
> do I need to place between the new jack and the leads, so the input
> works? The PDA must have some kind of preamp built in to drive the
> condenser mic, so I am thinking maybe some kind of resistor or volume
> control to "step down" the signal strength before it goes into the
> PDA's preamp? I suspect the audio fidelity won't be the greatest, but
> as long as it's passable I would like to try. Any info would be most
> appreciated... thanks.
Lots of luck! The audio input circuitry is almost surely only intended
for dictation. To save memory, the audio is very likely heavily
compressed so artifacts will really destroy any semblance of fidelity.
It also has very aggressive AGC that is great for dictation and
horrible for music. There are probably five other issues that will
further degrade music quality. BTW, the condenser microphone might be
the highest fidelity component in the PDA. How does music sound that
has been recorded with the microphone? It probably won't sound any
better using a hacked line input. You will get much, much, much better
results (and multiple channels) using some like a Zoom.
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Author: Richard CrowleyDate: 17:45 28-08-08
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"Mad Scientist Jr" wrote ...
>I have an old PDA that I would like to modify (if possible) by taking
> out the built in condenser mic and replacing it with a 1/8" or 1/4"
> jack that I can plug another device into.
The PDA must be *really old* to have enough space for a 1/4"
jack! :-) OTOH, the smaller 1/8" jacks might fit in the space
occupied by the mic capsule. Note, however that most 1/8"
jacks are configured to plug into the *side*, so you may have
a mechanical puzzle on your hands if the mic capsule isn't at
the edge of the enclosure.
> Mainly I want to plug a
> standard stereo headphone output (from iPod/cellphone/walkman/etc)
> although it would be cool to be able to connect a line-level out from
> a mixer,
Headphone level and *consumer* line-level are effectively
the same thing. Pro line-level is considerably higher and
would require additional attenuation.
> or directly plug a guitar in.
The output from a passive, high-impedance guitar pickup
may be too low (and the impedance too high) for the kind
of circuit typically used for built-in electret condenser mic
(ECM) capsules. OTOH, a single-transistor (FET) "preamp"
circuit could likely make it work. And it could be powered
from the same voltage already provided to run the FET in
the ECM. But the output from guitars with built-in buffer
amps (requiring a battery) would be closer to the level that
came out of the original ECM.
> The latter ones would probably
> require a different circuit so for simplicity I'll just stick to the
> first scenario (headphones out). Assuming I successfully can de-solder
> and remove the condenser mic from my PDA and have two leads (which
> went to the mic) free to solder my new input to,
Probably. But some ECM used three wires: ground, signal, and power.
> what kind of circuit
> do I need to place between the new jack and the leads, so the input
> works? The PDA must have some kind of preamp built in to drive the
> condenser mic, so I am thinking maybe some kind of resistor or volume
> control to "step down" the signal strength before it goes into the
> PDA's preamp?
Yes, you will almost certainly need to attenuate the signal so
it won't overload the existing input circuit. This can be as simple
as two very small resistors (an "L-pad").
> I suspect the audio fidelity won't be the greatest, but
> as long as it's passable I would like to try. Any info would be most
> appreciated... thanks.
That is a whole separate discussion and depends a lot on exactly
what old PDA you are talking about (undisclosed). But as others
have mentioned, likely none of them have any significant music-
quality performance.
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Author: whit3rdDate: 21:21 28-08-08
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On Aug 28, 10:33=A0am, Mad Scientist Jr <mad.scientist...@gmail.com>
wrote:
> I have an old PDA that I would like to modify (if possible) by taking
> out the built in condenser mic and replacing it with a 1/8" or 1/4"
> jack that I can plug another device into.
Why not just glue a bit of Velcro next to the microphone? A suitable
speaker-on-a-wire can be stuck on whenever you want. It can
be as simple as half a dead iPod earbud, or you can experiment with
matching transformers and/or amplifiers.
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Author: Bob MastaDate: 08:44 29-08-08
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On Thu, 28 Aug 2008 10:33:24 -0700 (PDT), Mad Scientist Jr
<mad.scientist.jr@gmail.com> wrote:
>I have an old PDA that I would like to modify (if possible) by taking
>out the built in condenser mic and replacing it with a 1/8" or 1/4"
>jack that I can plug another device into. Mainly I want to plug a
>standard stereo headphone output (from iPod/cellphone/walkman/etc)
>although it would be cool to be able to connect a line-level out from
>a mixer, or directly plug a guitar in. The latter ones would probably
>require a different circuit so for simplicity I'll just stick to the
>first scenario (headphones out). Assuming I successfully can de-solder
>and remove the condenser mic from my PDA and have two leads (which
>went to the mic) free to solder my new input to, what kind of circuit
>do I need to place between the new jack and the leads, so the input
>works? The PDA must have some kind of preamp built in to drive the
>condenser mic, so I am thinking maybe some kind of resistor or volume
>control to "step down" the signal strength before it goes into the
>PDA's preamp? I suspect the audio fidelity won't be the greatest, but
>as long as it's passable I would like to try. Any info would be most
>appreciated... thanks.
Fidelity will probably be poor by hi-fi standards, but fine for guitar. Mic
inputs typically include low-pass filtering to remove frequencies above 8k or 9k
or so (at least on laptops I've measured), but that's well above the guitar
range. The mic capsule has a single-FET "preamp" internally, powered either
by
a separate connection (3-connection capsule) or through a dropping resistor
(2-connection capsule). The case of the capsule is usually one of the
connections, and may go straight to the circuit ground. Or there may be a wire
to a pad on the capsule, with a very fine trace from the pad to the case. That
would be typical if the capsule is not mounted directly on a circuit board of
the PDA.
If you have the 3-connection style you can ignore the one going to the supply
voltage and feed your signal to the other 2. If you have the 2-connection style
with a dropping resistor, you will need to find the hot end of the resistor and
disconnect it before using the 2 leads.
Yes, you will probably need an attenuator, which can be a simple 2-resistor
divider.
Best regards,
Bob Masta
DAQARTA v4.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
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