Adapting a Telephone Handset to a Cell Phone

Step 3 Opening up the Wired Headset

Cell phone handsfree headsets also contain a microphone and one (or sometimes two) speakers. We are simply going to exchange the microphone and speaker in the old telephone handset for the microphone and one of the speakers in the modern handsfree headset. We are going to do this by cutting the plug off the modern handsfree headset and connecting it to the end of the coiled telephone cord. The trick is to connect together the correct wires.

What we need to do now is identify the wires in the handsfree headset cord. Since each headset is different, there is no one best approach. If your headset is similar to the one Im using in this example, youre in luck. If not, you will have to use this procedure as a guide and figure yours out.

If you can, the next step is to open the microphone enclosure on your handsfree headset. This will show you the wires and their functions. Figure 3 shows a microphone enclosure both "as built" and opened up.

The second image is a close-up of the "opened up" microphone enclosure, showing the identified wires. As in the first image, the speakers are on the left, and the connection to the cell phone is on the right.

Note how the red and green wires that go to the ear bud speakers pass directly through the microphone printed circuit board (PCB). The bare return wire, which is shared by both speakers and the microphone, is connected to a ground plane on the small PCB and passes up to the speakers. The white microphone wire comes in from the right (the side toward the cell phone) and dead ends at the microphone PCB.

So, now we know which wires to use.