Every once in a while, I get bitten by the bug to do some very geeky project. A couple of years ago, that project was to build an arcade cabinet. This week, I got the bug again, although to a much lesser degree. I've been trying to clear out all of the unnecessary stuff from my desk at work. I have piles of stuff I never use, and it clutters up the limited space I have. I had three PCs sitting under the desk that were switched off 90% of the time, and I had a three piece speaker set with a giant subwoofer that I never used. I always wear my headphones, and never use the speakers, but I plug my headphones into the speakers. It was time for all of this stuff to go.
After moving my speakers out, I plugged my headphones directly into the line-out jack on my Sirius radio. That's when I discovered my problem. The radio did not have a volume control. It was intended to be plugged into a stereo receiver, and the receiver would supply volume control. I was faced with a decision: spend $30 or more on a new set of headphones that had a built in volume control, or spend $15 to build my own volume knob. I knew that a volume know is just a variable resistor (Potentiometer) in line with the signal, and I had used them before in lab for class. I headed down to the radio shack and picked up a hobby kit, a nice shiny knob, and a good two channel potentiometer.
Potentiometers are pretty easy to use. In most cases, there are three solder points. You wire ground to one of the points, your source signal to the other, and the output to the one in the middle. As you dial the potentiometer back and forth, the resistance applied between the source signal and the output changes, and in effect changes the volume on the headphones. My potentiometer had two channels, one for the left speaker and one for the right. It was a simple matter to get the wiring done, and the dremel did nice work of poking holes in the sides of the hobby kit. And now, I have a fully functional volume knob!
Now that I'm done with this little project, I do have one thing I would have changed. I used a 100K Ohm potentiometer. That's a lot of resistance. I think my headphones only provide a 10K Ohm load, if that. The result is that I have to dial the "volume" on the potentiometer way up to hear anything, and once I do hear something, the knob is very sensitive to changes. A little to the right, and it gets very loud. A little to the left, and it goes silent. It works for what I need, but if I were to do it again, I'd get a much weaker potentiometer.
This was a fun little project that didn't cost a lot of money, and it let me geek out for a little bit.