JACK_INSERT and HOLD underlying issues

Werner Almesberger werner at openmoko.org
Fri Feb 29 12:05:51 CET 2008

Allen Chang wrote:
> When plugging the earphone, the HOLD voltage is still 3.2V.

Mystery solved. The microphone's resistance varies with the voltage
applied. It's roughly 1kOhm+4kOhm/V. 

The multimeter applied only a few millivolt, and thus saw a very low
resistance. With a 3.3V source through 2k2, we should get at least
2.8V, which is more than enough. Not sure why your measured value is
even higher, but we can worry about that another time ;-)

Thanks for checking this, and sorry for doubting you :-)

- Werner

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