Project: Headphone volume control

I recently moved to a new cell phone, a Motorola Triumph.  One of the first  problems I encountered has to do with the media volume.  A little background: I listen to music at work almost constantly from the moment I sit down at 8:00am until I pack up everything between 5:00 and 7:00 pm.  I keep it low enough to hear other things going on around me and usually have only one ear in, but I need the background to keep me occupied and entertained.  I have been using my Motorola Droid and streaming radio over 3G from Verizon (using my old unlimited data plan).

With the Triumph, I had two problems.  The first and more easily fixable problem, the 3G coverage from the Sprint network does not cut it at work.  Heck, I barely have enough signal to make a phone call.  But the solution is simple, to use the wifi at work.  Second, and not as easily fixable, is that the volume from my earbuds at the lowest volume setting is WAY too loud.  Like, other people can hear them loud, not to mention that I can’t hear anything else.

I looked for some software solutions in the android market (Google Play Store, whatever) and found plenty of apps to adjust the volume, but none that could adjust finer than the 15 levels (+off) that android already supports.  So, I decided to fix it in hardware!

My plan, to make an in-line volume control that I could plug in at the phone then plug headphones into.  This would also be viable for any other devices using 3.5mm jacks (such as mp3 player into a stereo), although I don’t need it anywhere else right now.

I did a little research, and of course other people have done this.  Which is good for me, because it helped me find what size potentiometer I wanted to use as a volume knob.  I used this instructable to find that I wanted a 1K audio potentiometer.  Which basically means 1 knob controlling 2 pots, one for left channel and one for right channel.  There are only 5 pins because the pots share 1 rail, which is used as ground (the audio channels already share ground).

The parts I needed:

– 3.5mm Male Stereo Audio Jack
– 3.5mm Female Stereo Audio Jack
– Small gauge Stereo Audio wire
– 1Kohm Thumbwheel Audio Potentiometer for Volume Control

Now, the instructable recommends (correctly) that you harvest the parts for this from other things.  I had all of these things easily accessible immediately, except for the potentiometer.  I would normally go ahead and rummage through my (junk) electronics piles and find one.  But I was in a rush and going to dinner at a friends house the night I decided to do this.  So, while still at work I looked at the Radioshack website and found something close.  It is a 10K volume wheel.  I decided this would be close enough with 1K resistors across the pots in parallel, turning them into 909ohm potentiometers.

Here are some excerpted images from the instructables article.

Again, my final product has a 10K potentiometer with 1K resistors in parallel.  You can’t see them below, but   they are there, under the wheel and above the headphone jack.  I used hot glue to hold it all together and add structural support when I plug and unplug headphones into it.

-KB1SVH