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'[OT] Recording to ISD-1400 Without a MIC?'
1998\06\20@154158 by Mark A Winters

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<DIV><FONT color=#000000 size=2>Hello All,</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Hopefully someone on this list has some experience with the
ISD audio recording/playback chips. If so, h</FONT><FONT color=#000000 size=2>as
anyone been successful recording to one of these chips directly using the
headphone output from a stereo or computer, rather than using a microphone as
input?</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>The circuit example that come with the datasheet
for the 1400 series shows a microphone input, though it also says that
&quot;...if the desired input is derived from a source other than a microphone,
the signal can be fed, capacitively coupled, into the ANA IN pin
directly.&quot;</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>Following this advice, I've hooked up the
negative headphone output from the stereo to the circuit ground, and have the
positive signal going through a .1uF capacitor and 100K pot (in series) to the
ANA IN pin on the 1400. When I attempt to record to the chip, I hear a loud
&quot;hum&quot; coming from the speaker. When I try to play it back, I don't
hear any audio, other than a &quot;click&quot; when it reaches the EOM
marker.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>Does anyone see anything wrong with this setup?
BTW, since I'm not using a microphone for input, I don't have anything connected
to the MIC, MIC REF, or ANA OUT pins, nor do I have anything connected to the
~RECLED pin other than a resistor and LED. (The application diagram shows this
pin also connected to the microphone components). I do have the AGC pin
connected to a resitor and capacitor as shown in the diagram.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>Any advice (or a pointer to a working circuit
diagram) would be greatly appreciated!</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#000000 size=2>Thanks,</FONT></DIV>
<DIV><FONT color=#000000 size=2>Mark</FONT></DIV></BODY></HTML>

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1998\06\20@161701 by WF AUTOMACAO

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Mark A Winters wrote:
>
> Hello All,
>
> Hopefully someone on this list has some experience with the ISD audio recordin
g/playback chips. If so, has anyone been successful recording to
one of these chi
>
> The circuit example that come with the datasheet for the 1400 series shows a m
icrophone input, though it also says that "...if the desired
input is derived fro
>
> Following this advice, I've hooked up the negative headphone output from the s
tereo to the circuit ground, and have the positive signal going
through a .1uF ca
>
> Does anyone see anything wrong with this setup? BTW, since I'm not using a mic
rophone for input, I don't have anything connected to the MIC,
MIC REF, or ANA OU
>
> Any advice (or a pointer to a working circuit diagram) would be greatly apprec
iated!
{Quote hidden}

May i help you? I have recording from a Sound Blaster output source!

I'm was using the ISD1420, now i use the ISD33...

Miguel.

1998\06\20@165227 by Sean Breheny

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On Sat, 20 Jun 1998, Mark A Winters wrote:

> Hello All,
>
> Hopefully someone on this list has some experience with the ISD audio =
> recording/playback chips. If so, has anyone been successful recording to =
> one of these chips directly using the headphone output from a stereo or =
> computer, rather than using a microphone as input?
>
> The circuit example that come with the datasheet for the 1400 series =
> shows a microphone input, though it also says that "...if the desired =
> input is derived from a source other than a microphone, the signal can =
> be fed, capacitively coupled, into the ANA IN pin directly."
>
> Following this advice, I've hooked up the negative headphone output from =
> the stereo to the circuit ground, and have the positive signal going =
> through a .1uF capacitor and 100K pot (in series) to the ANA IN pin on =

I think that this is your problem right here. The pot should NOT go in
series. Instead, connect the headphone neg. to circuit gnd, as you said,
then connect the headphone pos. to one of the end pins on the pot. Hook
the other end pin to gnd and the "wiper" or middle pin to ANA IN, via the
.1 uF cap. You also might consider putting an additional cap between the
headphone pos and the pot to prevent the phone from getting shorted if
the pot is turned all the way to one end. Use a 10K pot, not 100k.

> the 1400. When I attempt to record to the chip, I hear a loud "hum" =
> coming from the speaker. When I try to play it back, I don't hear any =
> audio, other than a "click" when it reaches the EOM marker.
>

The hum probably comes from the fact that you were effectively making the
ANA IN "float" due to the high impedance in series (100k). I don't think
that the ANA IN has that high an impedance.

{Quote hidden}

Good LUck,

Sean

1998\06\20@200353 by Martin McCormick

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       The microphone input is a _VERY_ sensitive circuit as audio inputs
go.  The optimum level is probably around 5 millivolts while the stereo
headphone output produces around 1-hundred times that amount without really
even trying that hard.  The name of the game is attenuation.  The pot is the
right idea but there are about 20 decibells or more too much audio.
What is needed is about 1 1-hundredth of that signal level at the maximum.

       Try the following circuit for starters:

       Find a fixed resistor that is about 100 times the resistance of the
element of the record level pot.  The audio from the stereo should connect
to one end of the resistor while the other end goes to the high end of the
pot.  The low end of the pot and the ground lead of the headphone output
need to both connect directly to the signal ground of the voice recorder
circuit.  The wiper of the pot should be capacitively coupled to whatever
circuitry the data sheet for the voice storage chip requires.  This gives
a variable record level that goes all the way from no signal at all to a
maximum of about 1/100 of the audio from the headphone output.  If you
omit the series resistor, there will be so much audio present that you will
probably have too much level almost as soon as the level pot is moved away
from the low stop.

       You may test this part of the circuit if you have a cassette tape
recorder that has an external microphone input.  You don't even need to power
your voice chip for this test.  Just connect the microphone input of the
cassette recorder between the wiper of the pot and ground and run some audio
to see if you can get a good but not too high level on the tape recorder.
Turning the pot should be just like turning any volume control so you can
check your input circuit before trying or frying anything else.

       A 10 K fixed resistor in series with a 100 ohm volume pot would give
you about the right amount of attenuation plus a low impedance output to the
voice recorder chip's input.  Your stereo would see essentially a 10 K load.


Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Data Communications Group

1998\06\20@235256 by Bill Colville

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> Hello All,
>
> Hopefully someone on this list has some experience with the ISD audio recordin
g/playback chips. If so, has anyone been successful recording to one of these ch
ips directly using the headphone output f>
> The circuit example that come with the datasheet for the 1400 series shows a m
icrophone input, though it also says that "...if the desired input is derived fr
om a source other than a microphone, the >
> Following this advice, I've hooked up the negative headphone output from the s
tereo to the circuit ground, and have the positive signal going through a .1uF c
apacitor and 100K pot (in series) to the >
> Does anyone see anything wrong with this setup? BTW, since I'm not using a mic
rophone for input, I don't have anything connected to the MIC, MIC REF, or ANA O
UT pins, nor do I have anything connected>
> Any advice (or a pointer to a working circuit diagram) would be greatly apprec
iated!
>
> Thanks,
> Mark

Mark,

I am using an ISD1416 to record the output from an 8 ohm speaker. I
finally had to use an 8 ohm to 1k isolation transformer between the
speaker and the two MIC inputs to get rid of the hum. I tried a
single ended input first without success. Going to a balanced
input, isolated from ground, cured the problem. I did not try the ANA
IN pin as I wanted to retain the filtering characteristics of the
coupling network.

Hope this helps.

Bill,  W3NMK

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