Axim: in-out audio cable (English)

As we all know the X50 and X51 series Axims, as well as other PDAs on the market, have a 4 pole 3,5 mm audio socket that allows to use a stereo headphone and an external microphone, but not at the same time. This can be achieved using an adapter cable. This adapter has a 4 pole jack on one end, from which two wires are departing with a line-socket on each end: one for the headset and one for the external microphone.

Although such adapters can be found for sale, (HERE and HERE 13$ + shipping), since the construction of this cable is very simple, I thought that someone could be interested in doing it by themselves, so I prepared this step-by-step how-to guide.

Let’s start from the material:

a) about 20 cm of electric cable with 3 wires;
b) about 15 cm of electric cable with 2 wires;
c) one 3,5 mm – 4 pole jack;
d) two 3,5 mm stereo (3 pole) line-sockets.

The cables have different length in order to be able to distinguish between the headset and the microphone terminal once the adapter is completed.
In this example I choose the shortest cable for the microphone.
The role of the 4 pole jack is to bring into the Axim the external microphone mono signal (2 conductor wire) and to send the stereo audio out signal (3 conductor wire) to the headset.
The functions of its 4 poles can be described as follows, from the tip to the sleeve of the jack:

1 - tip : audio out left channel;

2 - 1° ring : audio out right channel;

3 - 2° ring : microphone line in;

4 - 3° ring/sleeve : ground – common for microphone and audio out.

In the picture the corresponding internal soldering terminals are highlighted in orange.

The two stereo line-sockets have a ground contact and two signal terminals. Usually one of these terminals is copper coloured whilst the other is silver coloured, in order to help differentiating them.

Normally the silver coloured terminal corresponds to the tip of the equivalent male jack (left channel), whilst the copper one corresponds to the first ring (right channel). This conventional marking may vary depending on the socket manufacturer, so it is advisable to test the connectors before soldering, to be sure of the right channel assignment.

For the microphone both terminals should be connected to the same wire. Be aware that this is valid only for microphones with a stereo jack. In case of a mono jack, the first ring and the sleeve would be shortened and the external microphone disabled. In this case only the contact corresponding to the jack’s tip should be connected to the line.

For the headset, one is for the left channel (in this example the silver coloured terminal) the other for the right channel (in this example the copper coloured terminal).

Remember that in the headset stereo jack normally the tip is the left channel, the first ring is the right channel and the third ring/sleeve is the ground.

Enjoy!

P.S.: This adapter gives very good results when used with the Axim running on the internal battery. The use of an external power source, may induce some interference in the audio signal. This problem seems to be caused by the external noise being transferred to the power the Axim sends to the microphone and then amplified from the AGC and the amplifying circuitry of the audio section. The problem is solvable using an external powered microphone (this way the audio circuit senses that the microphone is self-powered and stops sending energy to it, and so the noise, that is hence not introduced in the amplifying circuitry); another solution is the use of an external auxiliary battery (noiseless power source) with high capacity; a last method would be to modify the PDA’s registry setting to stop power being sent to the external microphone. Out of these three methods, I applied the first two, which successfully solved the problem. For what the third is concerned, being unwilling to tweak with the registry settings, I didn’t even try.

Credits:

A big thank goes to prof. Gerald Maguire for having been very kind and helpful and for the useful advices about how to solve the noise issue.

Disclaimer:

the information in this guide is for informational purposes only. The author and X50v.it assume no liability for any inaccurate, delayed or incomplete information, nor for any actions taken in reliance thereon.