Hacking nokia headset HS-40 to work with OM
alberto.morales at galotecnia.com
Sat Sep 6 18:40:28 CEST 2008
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:
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:
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.
More information about the community