# PC microphone in voltage

G

#### Guest

##### Guest

Hi,

I work in an electrophysiology lab. This means we record
voltage/current changes in electrically excitable tissues
(nerves/muscles). If we had infinite funds, we would have an electrode,
attatched to a preamp, passed through an analogue to digital converted,
and into the back of a PC. However, we don't.

What I'm wondering is, would it be possible to input the analoge signal
into the 'microphone in' port on the PC once it had been amplified to
5v? More specifically (as I assume that must be possible) is the
microphone in port (on a standard onboard sound card) 0v to 5v or -5v
to +5v? Finally, what would the result be if the voltage crept above
5v?

Thanks to anyone who answers these questions, if any of them make sense

G

#### Guest

##### Guest

"bilz0r" <bilz0r@hotmail.com> wrote in message
> Hi,
>
> I work in an electrophysiology lab. This means we record
> voltage/current changes in electrically excitable tissues
> (nerves/muscles). If we had infinite funds, we would have
an
> electrode, attatched to a preamp, passed through an
analogue
> to digital converted, and into the back of a PC. However,
we
> don't.
>
> What I'm wondering is, would it be possible to input the
> analoge signal into the 'microphone in' port on the PC
once it
> had been amplified to 5v?

Mic in ports don't require and can't handle that kind of
signal voltage.

A line in input might require 1 volt rms.

A mic in input is at least 10 times more sensitive - 100 mv.

G

#### Guest

##### Guest

"bilz0r" wrote ...
> I work in an electrophysiology lab. This means we record
> voltage/current changes in electrically excitable tissues
> (nerves/muscles). If we had infinite funds, we would have
> an electrode, attatched to a preamp, passed through an
> analogue to digital converted, and into the back of a PC.
> However, we don't.

Before going much farther, you must specify what frequency
range you are interested in recording. I suspect that you may
need good response down close to DC (0 Hz) This is well
outside the capacity of almost ANY "audio" recording
devices or methodology.

> What I'm wondering is, would it be possible to input
> the analoge signal into the 'microphone in' port on the
> PC once it had been amplified to 5v? More specifically
> (as I assume that must be possible) is the microphone in
> port (on a standard onboard sound card) 0v to 5v or -5v
> to +5v? Finally, what would the result be if the voltage
> crept above 5v?

Mic inputs expect something closer to 0.01V (10mV).
Even the "line-level" inputs are designed for something
less than 1V.

Note that there are products designed for computers that
are A/D converters with frequency response down to
DC. They are called PC oscilloscopes. They will display
the waveform on the screen and I believe that some will
allow you to record the waveform for later playback or
analysis.

G

#### Guest

##### Guest

On 19 Jul 2005 22:45:35 -0700, "bilz0r" <bilz0r@hotmail.com> wrote:

>Hi,
>
>I work in an electrophysiology lab. This means we record
>voltage/current changes in electrically excitable tissues
>(nerves/muscles). If we had infinite funds, we would have an electrode,
>attatched to a preamp, passed through an analogue to digital converted,
>and into the back of a PC. However, we don't.
>
>What I'm wondering is, would it be possible to input the analoge signal
>into the 'microphone in' port on the PC once it had been amplified to
>5v? More specifically (as I assume that must be possible) is the
>microphone in port (on a standard onboard sound card) 0v to 5v or -5v
>to +5v? Finally, what would the result be if the voltage crept above
>5v?
>
>Thanks to anyone who answers these questions, if any of them make sense

A Mic In typically accepts up to 100mv. If you have a Line In this is

What sort of frequency signal are you creating? These inputs expect
audio signals. Response to lower frequencies could be problematic.
But it shouldn't be too hard to arrange a suitable voltage. Try.

#### gregs

##### Distinguished

In article <1121838335.262374.258060@g44g2000cwa.googlegroups.com>, "bilz0r" <bilz0r@hotmail.com> wrote:
>Hi,
>
>I work in an electrophysiology lab. This means we record
>voltage/current changes in electrically excitable tissues
>(nerves/muscles). If we had infinite funds, we would have an electrode,
>attatched to a preamp, passed through an analogue to digital converted,
>and into the back of a PC. However, we don't.
>
>What I'm wondering is, would it be possible to input the analoge signal
>into the 'microphone in' port on the PC once it had been amplified to
>5v? More specifically (as I assume that must be possible) is the
>microphone in port (on a standard onboard sound card) 0v to 5v or -5v
>to +5v? Finally, what would the result be if the voltage crept above
>5v?
>
>Thanks to anyone who answers these questions, if any of them make sense

A basic AD for a PC is quite cheap??
Your range of frequencies are likely to be very low, at near DC to some higher
value. I don't know the lower limit of sound cards. It would seem like your
specifying 0 to 5 v is for actual signal. Again, depending on your signal levels, a
differential amp signal conditioning circuit, along with a converter
to change signal to a higher modulation frequency might work. Demodulating
the signal for retrieval would be needed when playing back.!! ??
Many labs in the past, used to record DC through audio range by using old Sony PCM
to Beta recorders, by converting them for DC signals, by bypassing the coupling caps.

greg

G

#### Guest

##### Guest

Thanks for all the replies everyone.

Well, I would typically digitize at somewhere around 3-10kHz. We
wouldn't need to be able to pick up slow occilations (in fact it would
be good if it would ignore everything below 50Hz, but we have a 50Hz
filter inline anyway, but the AC coupling doesn't really matter (though
thanks for poitning that out)). The record doesn't need to be 100%
accurate anyway, as we would have a DAT recorder inline, picking up the
signal straight out of the preamp.

So when people are saying "respond down to DC" I don't quite
understand. Just low amplitude signals? Or DC voltage offsets?

So the conclusion is that the line-in port takes higher voltage values
(-1v to 1v) and the mic in port takes voltages some 100x lower (-10mV
to 10mV)? And what would the result of an input of a DC voltage above
those limits?

(to the person who mentioned a PC occiloscope, that is essentially what
I'm trying to achieve, without the purchase of any specially designed
cards)

> On 19 Jul 2005 22:45:35 -0700, "bilz0r" <bilz0r@hotmail.com> wrote:
>
> >Hi,
> >
> >I work in an electrophysiology lab. This means we record
> >voltage/current changes in electrically excitable tissues
> >(nerves/muscles). If we had infinite funds, we would have an electrode,
> >attatched to a preamp, passed through an analogue to digital converted,
> >and into the back of a PC. However, we don't.
> >
> >What I'm wondering is, would it be possible to input the analoge signal
> >into the 'microphone in' port on the PC once it had been amplified to
> >5v? More specifically (as I assume that must be possible) is the
> >microphone in port (on a standard onboard sound card) 0v to 5v or -5v
> >to +5v? Finally, what would the result be if the voltage crept above
> >5v?
>
> You would want to use the Line In, and it would vary in sensitivity
> based on the recordiig volume (double-click the speaker icon,
> options->properties->recording). If you want to put in more than 0 to
> 3V or so, you need an attentuator (and probably active electronics,
> depending on the impedance of what you want to measure). Also, as
> someone else mention, all soundcards are AC-coupled and won't give
> good response below 20Hz or so.
> Here's a few things from a seismology list (seismicnet.com): If
> your amount of funds is literally zero and you can handle a soldering
> iron, this (modifying a soundcard to respond down to DC) may be of
> interest:
>
> http/www.qsl.net/om3cph/sb/dcwithsb.htm
>
> But I think that's a dodgy kludge.
>
> This is a lot less than infinite funds, and is really cheap
> (pricewise) for anything labeled "Data Acquisition":
>
> http/sine.ni.com/nips/cds/view/p/lang/en/nid/14604
>
> >
> >Thanks to anyone who answers these questions, if any of them make sense
>
> -----

G

#### Guest

##### Guest

On 19 Jul 2005 22:45:35 -0700, "bilz0r" <bilz0r@hotmail.com> wrote:

>Hi,
>
>I work in an electrophysiology lab. This means we record
>voltage/current changes in electrically excitable tissues
>(nerves/muscles). If we had infinite funds, we would have an electrode,
>attatched to a preamp, passed through an analogue to digital converted,
>and into the back of a PC. However, we don't.
>
>What I'm wondering is, would it be possible to input the analoge signal
>into the 'microphone in' port on the PC once it had been amplified to
>5v? More specifically (as I assume that must be possible) is the
>microphone in port (on a standard onboard sound card) 0v to 5v or -5v
>to +5v? Finally, what would the result be if the voltage crept above
>5v?

You would want to use the Line In, and it would vary in sensitivity
based on the recordiig volume (double-click the speaker icon,
options->properties->recording). If you want to put in more than 0 to
3V or so, you need an attentuator (and probably active electronics,
depending on the impedance of what you want to measure). Also, as
someone else mention, all soundcards are AC-coupled and won't give
good response below 20Hz or so.
Here's a few things from a seismology list (seismicnet.com): If
your amount of funds is literally zero and you can handle a soldering
iron, this (modifying a soundcard to respond down to DC) may be of
interest:

http/www.qsl.net/om3cph/sb/dcwithsb.htm

But I think that's a dodgy kludge.

This is a lot less than infinite funds, and is really cheap
(pricewise) for anything labeled "Data Acquisition":

http/sine.ni.com/nips/cds/view/p/lang/en/nid/14604

>
>Thanks to anyone who answers these questions, if any of them make sense

-----

G

#### Guest

##### Guest

"bilz0r" wrote ...
> So when people are saying "respond down to DC" I don't quite
> understand. Just low amplitude signals? Or DC voltage offsets?

You clarified that the bandwidth of interest was 3-10KHz.
Some types of electrophysiology measurement may require
a lower frequency range but you didn't specify the range of

> So the conclusion is that the line-in port takes higher
> voltage values (-1v to 1v) and the mic in port takes
> voltages some 100x lower (-10mV to 10mV)? And what
> would the result of an input of a DC voltage above
> those limits?

Clipping distortion. In the input amplifier circuitry and/or
in the analog-to-digital converter circuit.

AC or DC, it makes no theoretical difference. In practice,
the AC-coupled sound cards will pretty much ignore most
of the DC.

> (to the person who mentioned a PC occiloscope, that is
> essentially what I'm trying to achieve, without the purchase
> of any specially designed cards)

There are several cheap-ware and free-ware PC oscilloscope
They use ordinary PC sound cards. From your clarification of
couple of them.

G

#### Guest

##### Guest

"bilz0r" <bilz0r@hotmail.com> wrote in message
> Hi,
>
> I work in an electrophysiology lab. This means we record
> voltage/current changes in electrically excitable tissues
> (nerves/muscles). If we had infinite funds, we would have an electrode,
> attatched to a preamp, passed through an analogue to digital converted,
> and into the back of a PC. However, we don't.

Can you describe the signals, and what data you are trying to capture?

There are low-cost programmable devices such as the PIC microconroller

http/www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=74

Tim

G

#### Guest

##### Guest

On Wed, 20 Jul 2005 19:27:02 GMT, Ben Bradley

> You would want to use the Line In, and it would vary in sensitivity
>based on the recordiig volume (double-click the speaker icon,
>options->properties->recording).

This control generally attenuates the level in digital domain, after
it has passed through the a>d convert or. It is no protection against

G

#### Guest

##### Guest

On 20 Jul 2005 18:17:19 -0700, "bilz0r" <bilz0r@hotmail.com> wrote:

>Well, I would typically digitize at somewhere around 3-10kHz.

You know, it would have been REALLY useful to have stated this at the
outset

G

#### Guest

##### Guest

This may be of interest to you...

http/www,akrobiz,com/laserboy/

This is a DC modified cheapo sound card that I am using as an output device
to generate the signals necessary to control a color laser projector. The
outboard electronics sum a negative voltage with the output of the card to
bring the all positive signal back down to center over the zero volt line
and give the output enough voltage gain to drive the laser scanner amps and
color modulators.

If you short out the input decoupling caps, then you can record DC offsets
or AC signals that are not necessarily centered over the zero volt line. If
you exceed the recording input voltage limits, then your recorded data will
simply max out at either the positive or the negative extreme and your data
will not be accurate.

I also developed a method of measuring frequency vs. voltage and phase angle
over the entire audio spectrum using a sound card to play a mathematically
derived signal and simultaneously record it back in again and figure out the
difference in amplitude and phase. Getting the output to sync down to the
sample with the data coming back in was quite a trick.

I used this to measure all sorts of thing while I was designing these
speakers:
http/www.akrobiz.com/speakers/metal_index.html
http/www.akrobiz.com/speakers/metal-graphs.html

~James. )

"bilz0r" <bilz0r@hotmail.com> wrote in message
> Hi,
>
> I work in an electrophysiology lab. This means we record
> voltage/current changes in electrically excitable tissues
> (nerves/muscles). If we had infinite funds, we would have an electrode,
> attatched to a preamp, passed through an analogue to digital converted,
> and into the back of a PC. However, we don't.
>
> What I'm wondering is, would it be possible to input the analoge signal
> into the 'microphone in' port on the PC once it had been amplified to
> 5v? More specifically (as I assume that must be possible) is the
> microphone in port (on a standard onboard sound card) 0v to 5v or -5v
> to +5v? Finally, what would the result be if the voltage crept above
> 5v?
>
> Thanks to anyone who answers these questions, if any of them make sense
>

G

#### Guest

##### Guest

Oooops!
http/www.akrobiz.com/laserboy/

Freakin' comma!

"James Lehman" <james[remove]@akrobiz.com> wrote in message
> This may be of interest to you...
>
> http/www,akrobiz,com/laserboy/
>
> This is a DC modified cheapo sound card that I am using as an output
device
> to generate the signals necessary to control a color laser projector. The
> outboard electronics sum a negative voltage with the output of the card to
> bring the all positive signal back down to center over the zero volt line
> and give the output enough voltage gain to drive the laser scanner amps
and
> color modulators.
>
> If you short out the input decoupling caps, then you can record DC offsets
> or AC signals that are not necessarily centered over the zero volt line.
If
> you exceed the recording input voltage limits, then your recorded data
will
> simply max out at either the positive or the negative extreme and your
data
> will not be accurate.
>
> I also developed a method of measuring frequency vs. voltage and phase
angle
> over the entire audio spectrum using a sound card to play a mathematically
> derived signal and simultaneously record it back in again and figure out
the
> difference in amplitude and phase. Getting the output to sync down to the
> sample with the data coming back in was quite a trick.
>
> I used this to measure all sorts of thing while I was designing these
> speakers:
> http/www.akrobiz.com/speakers/metal_index.html
> http/www.akrobiz.com/speakers/metal-graphs.html
>
> ~James. )
>
>
>
> "bilz0r" <bilz0r@hotmail.com> wrote in message
> > Hi,
> >
> > I work in an electrophysiology lab. This means we record
> > voltage/current changes in electrically excitable tissues
> > (nerves/muscles). If we had infinite funds, we would have an electrode,
> > attatched to a preamp, passed through an analogue to digital converted,
> > and into the back of a PC. However, we don't.
> >
> > What I'm wondering is, would it be possible to input the analoge signal
> > into the 'microphone in' port on the PC once it had been amplified to
> > 5v? More specifically (as I assume that must be possible) is the
> > microphone in port (on a standard onboard sound card) 0v to 5v or -5v
> > to +5v? Finally, what would the result be if the voltage crept above
> > 5v?
> >
> > Thanks to anyone who answers these questions, if any of them make sense
> >
>
>

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