Hacking nokia headset HS-40 to work with OM

[Rui Miguel Silva Seabra]

On Sat, Sep 06, 2008 at 05:40:28PM +0100, Alberto Morales wrote:
> Hello,
> 
> Nokia HS-40 is a cheap mono headset that has a 2.5mm jack with 4 rings. 
> It costs 9 EUR in spain. The pinout is INCOMPATIBLE with OM, hence nokia 
> pinouts are incompatible with OM. Here it is the Nokia HS-40 pinout:
> 
> Nokia HS-40 pinout:
> 1 (tip)  - left (R=34 ohm to ground)
> 2        - unused (in stereo models, probably connects right)
> 3        - mic (mic resistance 1K1 to ground, if button is pressed 48R)
> 4 (base) - ground
> 
> From this message, here it is the OM pinout: 
> http://lists.openmoko.org/pipermail/community/2008-March/013792.html
> 
> Openmoko pinout:
> 1 (tip)  - mic (2K2 ohm and 0R if button is pressed)
> 2        - right
> 3        - left
> 4 (base) - ground
> 
> If we plug the headset in the OM, only one speaker would work (i never 
> did it). This was reported by David Pottage in this message: 
> http://lists.openmoko.org/pipermail/community/2008-August/028219.html
> 
> I stopped measuring and began hacking ;-) The little box which has the 
> mic and the button, has two screws. If you remove them and open the 
> case, you'll see 3 wires + 1 wire shielding coming from the jack. It 
> should be 4 wires + shield, but nokia removed the unused wire from right 
> speaker. Get a multimeter and find the wires that connect with pin 1 and 
> 3 of the jack. Take a solder iron and swap wires from 1 and 3, and you 
> have a headset with a pinout compatible with OM.
> 
> I plugged the headset in the GTA02 and loaded the gsmheadset.state 
> during a call. I only had to increase the gain of the output from 80% to 
> 95% because the output from speaker was very low. 34R is below the 40R 
> minimum impedance that joerg recommended in his message. Microphone is 
> ok and people heard me fine. GSM buzz from 
> https://docs.openmoko.org/trac/ticket/883 is still randomly heard by the 
> other end (slight in local).
> 
> Button doesn't activate anything in the GTA02. I don't know if it 
> should. The 48R smd resistance can be easily transformed into a 
> shorcircuit if needed.
> 
> I have a few photos, i could create a nokia headsets section in the wiki 
> if you think is useful.

Yes, please do it, including photos :)

It's much better that it resides in the wiki than here!

Please tell us the URL when you're done :)

Congratulations,
Rui

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