Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <shngj0tbc7vf0dt617qfvrdkhihuc3ninn@4ax.com>, Eric Furness
<ericfurn@rcn.com> wrote:
> I cannot get the mike input on MB to work with Andrea NC-50 headset.
> The headset does work with a Santa Cruz sound board in another
> computer. There appears to be no power to mike on ring. If I feed
> audio into mike input from active audio source other than mike it does
> work. ??
> Eric
I would have expected to find a 2K ohm pullup to +5V on the "ring"
of the mic input on the back of the computer. You could test for
this in a safe way, with a 2K ohm resistor from Radio Shack (or
get the next nearest value, like 2.2K is good enough for this
experiment). You would need a male to male 1/8" cable, to get
access to the tip, ring, and sleeve contacts.
If you connect a voltmeter to "ring" and "ground" on the mic input,
without a load, you would get 5V. Placing the 2.2K resistor
across "ring" and "ground", will reduce the DC voltage seen to
roughly 2.5V, by voltage divider action. You can use the actual
voltage you see, to estimate what resistor is being used on the
motherboard. For example, if the motherboard actually uses a
1K resistor:
+5VA
|
1K motherboard resistor
|
+-------"Ring" <----- Voltmeter sees...
| |
2.2K test resistor +---- 2.2
| | ------- * 5V = 3.44V
+-------"AGND" <----- 2.2+1.0
(If motherboard resistor is 2K ohms, measured value is 2.62V)
Check to see if you have an FP_AUDIO header on the motherboard.
It is a 2x5 array of pins, with two default jumpers from the
factory installed. (Leave the jumpers there, as they are necessary
for Lineout on the back of the computer to work. If you get a cable
assembly intended for an Intel Audio header, then the jumpers can
be removed and the 2x5 cable assembly plugged into the header.)
An option is to wire up a front panel microphone jack on
your computer case. Some computer cases already have a jack and
a set of wires. The FP_AUDIO header has signals with names like
MIC2 - goes to "Tip" (select MIC2 in mixer panel ?)
MICPWR - goes to "Ring" (probably a 2K ohm to +5V supply)
AGND - goes to "Sleeve"
A possible problem with your NC-50, is maybe it needs something
other than whatever resistor is on the Asus motherboard (2K assumed
by me). The +5VA header pin, is a raw and dangerous source of
clean +5 for powering a microphone. You could try various
resistor values running from +5VA to "Ring", until the volume
improves. I.e.
MIC2 ----------------- "Tip"
+5VA ---2K_resistor--- "Ring"
AGND ----------------- "Sleeve"
I would try 1K ohm and 10K ohms as other values. 1/4 watt or 1/8th
watt leaded resistors from Radio Shack would work. (Maybe the
smart guys at AndreaElectronics.com tech support can tell you
what value the product needs ?)
The tough part will be wiring it all together. Radio Shack should
sell a stereo jack, but the hard part will be finding mating devices
to plug onto the pins on the FP_AUDIO header. Frontx.com sells bits
and pieces:
http://frontx.com/order_c.html
CPX075-9 Single pin plastic shroud (three needed to connect to
MIC2, MICPWR or +5VA, and AGND). Extra ones could be used
to hold onto the resistor.
CPX076 Ten pack of female pins. You crimp (squeeze) one end of
one of these onto a stripped end of a stranded wire.
The other end slides into CPX075-9, and when it is pushed
into place, a small plastic tab on CPX075-9 holds the
female pin in place. The plastic tab can be manipulated
with the tip of a narrow hobby knife, such that it will
release the pin and allow it to be removed, if repairs
are required. (
http://frontx.com/crimp.html )
The easy way is
http://frontx.com/cpx110.html
The CPX110 does it all for you, but it will connect MICPWR to
"Ring". So, CPX110 won't allow you to experiment with different
resistor values.
I don't know why the rear mic input doesn't have power on it.
On systems where 2, 4, 6 speaker modes use up to all three
rear jacks, there is multiplexing of the functions. Since
you were able to get some signal into the microphone jack,
that implies the speaker mode is not set to greater than
2 speaker mode. What is supposed to happen, is when the jack
is in speaker mode, the microphone stuff is disconnected. When
the speaker mode changes, a GPIO pin changes states, and that
controls the connecting of a 2K resistor to "ring", to power an
electret microphone. That is how multiplexed, three jack
motherboards are supposed to work - five jack motherboards have
dedicated functions and no multiplexing. Try using 2 speaker mode
first, before giving up.
Hope that gives you a few ideas,
Paul
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