headphone (was: RE: Price of the Freerunner spare parts)

[joerg]

Am Mi  26. März 2008 schrieb Marcus Bauer:
> On Tue, 2008-03-25 at 18:58 -0700, steve wrote:
> 
> > But onto your specifics:
> > 
> >  
> > 4. Headsets. It’s a standard part.  
> 
> Hi Steve,
> 
> I looked on the wiki pages but can't find the specs. As nokia headsets
> with a 2.5mm plug don't work (different wiring and impedance) there are
> apparently several standards for headsets.
> 
> Can you tell us which wiring the jack uses and what impedance the
> earplugs have?

[from a previous msg in this list]
Am Di  4. März 2008 schrieb Gilles Casse:
> Hi all,
> 
> I am a little bit embarrassed: my audio headset is lost, another one
> bought recently is not compatible (a 4 ring model for a Nokia, the
[...]

base = ground 
speaker left  (internal impedance 33R) to ground. (+jackinsert detection)
speaker right (internal impedance 33R) to ground.
tip = mic electret condenser type, to ground. 
      bias (power for mic) 2K2 from +3.3v(wolfson codec) 
      (+HoldButton shortcircuit to ground)

Due to the internal 33R resistors, any low impedance headset will not work (or 
only low sound). I guess 40R should be minimum impedance for the speakers.

cheers
jOERG