BackgroundDissatisfied with the standard headphone quality that shipped with my HTC phone, but not wanting to leave the ability to control the media application behind I designed and build an adapter which allowed any headphone to be plugged in to a custom controller.
Inspired by a Hackaday.com article which described the method by which these controllers worked, it was a very straightforward matter to design a simple controller.
The technical details revolved around grounding the function contact via different resistances:
- ~220 Ohms to skip back
- ~600 Ohms to skip forward
- 0 Ohms (short circuit) to pause/play
The main design aim however, was to make this as small and unobtrusive as possible, and package it attractively.
Designing a small device meant two things:
- Using a custom PCB
- Using small components
Designing a custom PCB was a matter of messing around in Eagle, but finding small, cheap tactile buttons proved to be challenge.
The components I settled on are listed below:
- 3x SMD Tactile buttons (Jaycar SP0610 - note pack of 10)
- 1x SMD 3.5mm Audio Jack (Element14 1216980)
- 1x 0805 SMD 220 Ohm Resistor (Element14 1469899)
- 1x 0805 SMD 560 Ohm Resistor (Element14 1646455)
- 1x TRRS 3.5mm patch cable (eBay)
- 1x PCB
- Some 10mm heatshrink
Printed Circuit Board
The board was designed in Cadsoft Eagle, and unfortunately uses two layers rather than just a single one - so etching it at home becomes a lot more difficult.
To manufacture the boards I used seeedStudio's Fusion PCB service. I was very happy with the speed and quality (especially for the price), they even threw in a bunch of extra boards on top of the 10 that I ordered.
I actually have a couple of spares that I can mail out, so send me an email if you're interested.
A reader, Fahad Alduraibi, has contacted me with two tweaked version of my PCB!
A few notes should be added at the end here, firstly, this version of the controller does not have a microphone and some phones seem to assume that it is present, which means that you have to unplug everything if you get a phone call while the controller is plugged in (assuming you want to talk to the person who is calling you...). Perhaps a later version of the board will have a microphone (I couldn't source any piezo mics small enough when I looked).
Secondly, the heatshrink "case" isn't waterproof. I can't imagine that getting it wet would do much damage, but I have been wrong before. I wouldn't recommend submersing it.
All files are licensed under the Creative Commons Attribution-ShareAlike license (CC BY-SA)Eagle design files: