Audio Jack Sampling Rate?

Charles Pax charles.pax at
Sun Sep 21 18:15:13 CEST 2008

On Sat, Sep 20, 2008 at 8:42 PM, Al Johnson
<openmoko at>wrote:

> You probably want to look at these two. The main limitation is that you've
> only got one input channel via the jack, but you might be able to get round
> that using the mic switch detection.

I incorrectly assumed there is stereo input on the jack. I'll have to go
back and rethink this whole thing. What is the mic detection switch? Can I
record audio from the mic input and the built-in microphone at the same

> Since you need external bits for the IR anyway you may be better off making
> a
> USB device instead. The arduino and other similar devices make the USB part
> relatively easy. Put a narrow bandpass filter on your audio transducer and
> you make the audio signal a simple on/off - use multiple frequencies if you
> need to track different markers or indicate different states.

I'm hoping to find some novel way of doing this with the most simple
hardware setup possible. Maybe we can have each transducer connected to a
bandpass filter that activates an oscillator. If the two oscillators operate
at different frequencies on the same mic-in channel, we should be able to
process this in software on the Freerunner to calculate when each oscillator
was triggered. This would allow us to use only dumb and cheap hardware that
should work on any computer with a mic-in. The IR detector(s) can also be
connected to a oscillator operating at a third frequency.

What do you mean by "external bits for the IR"? Data bits or just little
pieces of hardware? I figure a photodiode can be connected between signal
and ground. When suficient IR light hit it the diode should make a spike on
the mic-in channel.

-Charles Pax
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