[Hardware Hacking General] AdamOutler:
Hey guys, I worked on adding external microphone features to my device for a dog-gone long time yesterday... about 5 hours. Elite Recognized Developer Rebellos searched the code and we figured out that the device wouldn't recognize my mic because it's ohms are too low. The WolfsonMicro chip uses any value below 1000 ohms to signify button presses. Above 1000 ohms it signifies a microphone. My microphone is a 900 ohm microphone, so in all actuality, it's pretty high considering most are around 100-500 ohms. However, Rebellos and I managed to hack through it. I wanted to share this method.

My target device is a Galaxy Camera, but Samsung has used WolfsonMicro chips in their devices for a long time. This also works on the Galaxy Note 2 so Its logical to assume it will work on others.

Here's the finished solution. A Samsung 4-pole to 1/4" Mic adapter with a 200ohm resistor inline.

Introduction

The Galaxy Camera and Note2 require over 1000 ohms of resistance in order to recognize that a microphone is connected to it. So, there's two ways to do this.

1. Buy a microphone with over 1000 ohms of impedance.

2. Add some impedance.

Now, adding impedance will reduce the volume of the microphone, but that's not an entirely huge issue as adjusting volume is not a big deal. However, adding a resistor will slightly distort the waveform but even with this slight distortion it's not going to destroy the sound quality because it's a very slight ripple which in most cases will not affect the compressed recording quality.

Getting things together

Everything you need to add external, directional audio is available at Radio Shack for less than $35 USD. Buy a better microphone with higher ohms for louder sound. You get what you pay for.

1. 1/4" Mono In-Line Audio Jack (2-pack) - RS Part Number 274-0340 - $5

2. a set of Samsung Earbuds with 4-pole connections

3. optional - microphone Unidirectional Dynamic Microphone - RS Part Number 3303038 - $19.99 - note the old one is 900ohms. The new one is 600 ohms.

4. optional - Biasing Resistor - you will need to do the following equation to determine the ohmage of resistor you require. $5

1100 ohms - (ohms of your microphone stated in the manual) = ohms of resistor required to turn on the microphone.

1100 ohms - 900 ohms = 200 ohms of resistance required

5. Epoxy and Superglue $5

Building the adapter

Building the adapter is quite simple Samsung uses 7 wires in their headphones. Bare wire is not connected to anything. 3 are copper colored in clear shields there is a Blue or Green, Red and White as well. The 3 copper are the common leads The White is the microphone.

Cut the connector off the headphone, leaving 3 inches of the cable.

Cut all of the wires except for one Copper and the White wire.

Strip and tin the Copper and White wires.

Solder the copper wire to one side of the 1/4" Mono In-Line Audio Jack

*Optionally* If required to exceed 1100ohms solder the resistor to the white wire

Attatch the white wire (with resistor if used) to the center post of the 1/4" Mono In-Line Audio Jack.

At this point you can verify your setup works.

superglue the wire to hold it in place for the next step

Mix up your epoxy and apply to the resistor, wire and jack connections in a way to support the following:

1. to keep the wires from touching anything

2. to prevent physical strain on the electrical connections

You'll want to ensure that the epoxy is a light coat which totally surrounds the wire, resistor and large metal pads on the 1/4" audio jack. But don't let it go down inside the jack because it can prevent the microphone from connecting properly.

slide the 1/4" jack cover down over the epoxy after it's done drying.

It should look something like this:

Here's a video showing how it works with my cheap microphone. It works super well to remove almost all noise from my recordings and just needs about a 6db gain and bass-boost adjustment in post-processing for accurate sound reproduction. This could be and will be corrected with a better mic in the future.

[youtube]LmRc69Qe1FI[/youtube]