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bamse
16-03-2003, 11:15 AM
Hi guys,

I'm planning to mod my cradle by adding a small microphone connected to the CAR_MIC_IN connector and a standard stereo 3.5mm jack connected to the CAR_AUDIO_L/R connectors. The stereo jack will be used to plug in either a normal set of headphones, or connect to the line-in on the computer.

On the "XDA connectors" page it is said that "Audio needs to be capacitively coupled in". What does this actually mean? Do I need to put something between the XDA connector and the jack?

Which impedance would be suitable for the microphone? I can find anything from 200ohm to 2kohm at the shop.

I'll post a step-by-step howto for publication on this site when I have a working mod.
Peter Poelman
16-03-2003, 01:26 PM
I'm planning to mod my cradle by adding a small microphone connected to the CAR_MIC_IN connector and a standard stereo 3.5mm jack connected to the CAR_AUDIO_L/R connectors. [...]


Excellent project...

On the "XDA connectors" page it is said that "Audio needs to be capacitively coupled in". What does this actually mean? Do I need to put something between the XDA connector and the jack?

What that means is you take a small non-polar (i.e. tantalum) capacitor (experiment. I seem to remember we used 20 pF), and put the audio signal through it. This removes any DC bias, i.e. it makes the audio signal revolve around 0 V.


Which impedance would be suitable for the microphone? I can find anything from 200ohm to 2kohm at the shop.

We haven't played with it too long, but we suggest experimenting with a number of the circuits from this site:

http://www.hut.fi/Misc/Electronics/circuits/microphone_powering.html

I'll post a step-by-step howto for publication on this site when I have a working mod.

Excellent. Looking forward to it.
Carlos
18-03-2003, 01:34 AM
Keep in mind something that I've learned the hard way. You NEED a powered mic with this device. A typical non-powered version just does not work.
Anonymous
22-03-2003, 03:33 PM
What that means is you take a small non-polar (i.e. tantalum) capacitor (experiment. I seem to remember we used 20 pF), and put the audio signal through it. This removes any DC bias, i.e. it makes the audio signal revolve around 0 V.


For a stereo output this would mean three capacitors? One for each signal and one for the common ground?
climber
23-03-2003, 01:59 AM
No 2: one for each signal line.

Robert
Peter Poelman
23-03-2003, 09:43 AM
No 2: one for each signal line.
No, I was talking about the (mono-)input line, not the audio outputs.
Carlos
24-03-2003, 08:24 PM
No, just a single cap on the Mic line, nothing on ground lines.