Rotary Dial Phone Revival – 3 – The Headset

This is the next piece of work after step 2 that dealt with the ringing bells, and now it’s time to look into the headset and how we can connect this to the new brain of the phone.

Small detail, but before doing anything else I had to fix a problem with the wires that were half broken at the point where they enter the headset, most certainly due to all these years of usage, and the plastic strain relief not being well designed or of good enough quality.

This would lead to the sound being randomly interrupted or produce crackling noise, which was very annoying.

I initially connected the old headset directly to the existing microphone and speaker on the Tilda Mk4 board (after simply de-soldering the originals).  However, while the speaker was working OK, the microphone was probably too different in specs as the sound quality was bad.

Moreover, the old headset used only 3 wires, with a common ground, whereas on the new board the microphone and the speaker didn’t share any of the 4 connections.

After much back and forth I finally managed to fry the microphone input to the SIM800 module on the new board.

This forced me to take another approach, the only other one available, which was to use a bluetooth headset. Enter the Sephia S6, simply the cheapest, reasonably looking such device that I could find on Amazon and that also included a microphone.

As soon as I received it, I eagerly took it apart hoping that the size of the speakers and of the board would be OK relative to the old headset.

Everything seemed fine, except that the board was too large to fit where the old microphone was. I went ahead and “trimmed” it, and trimmed it again, and repeated a few more times, and it surprisingly continued to work  !


This proved to be unnecessary in the end, as on this board the microphone and the speaker shared a common ground, which meant that I could have it sit in the main body of the phone, right next to the main board, and use the 3 existing wires.

This setup feels more “realistic” than having the bluetooth board in the headset and use the existing wires just for power.

More importantly, it means that I can connect this “daughter” board to the main one, as the former needs to have a button pressed to be turned on / off.

With this approach, all that was left doing was to hot glue the new speaker and microphone in the old headset, and the result works surprisingly well.

Last but not least, there was some exploratory work around how to control the Sim800 module to properly pair and then connect to the new bluetooth headset. Here are a few useful commands:

import sim800

sim800.btpair(1) # the id of the bluetooth headset
sim800.btpaired() #should display the new "S6"
#<span id="mce_SELREST_start" style="overflow:hidden;line-height:0;">&#65279;</span>sim800.btgetprofiles()
sim800.btconnect(1, 6) # this corresponds to Hands-Free Profile (HFP). IMPORTANT otherwise the microphone doesn't work

One Response to Rotary Dial Phone Revival – 3 – The Headset

  1. Pingback: Rotary Dial Phone Revival – 4 – Final | Robotics / Electronics / Physical Computing

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