When choosing a case for the assignment, make sure it is big enough to hold the circuit board and the two 9-volt batteries with ease. Check to make sure all the controls and jacks will fit after the front panel is laid out and drilled. A way for labeling the front panel is to spray the entire thing with a flat color like yellow or white. Seal the panel when you have applied the transfer letters. Use many thin coats of a clear coating like Crystal Clear by Krylon. A lot of effort, but the results pay off. We can begin on the headphones while the front panel is drying.
Headphones with Ears. The headphones are an ordinary pair of aftermarket Walkman-type units. They are sold for around $20 at the majority of record or electronic businesses. The headphones are altered by attaching two small electret-condenser microphones on the headphones, one on each earpiece.
The trick to making the headphones wearable is by using thin wires going to the microphones. An exceptional source of thin audio cable is to purchase another set of cheap headphones the cheaper, the better. Cutting the wire off them will produce a shielded stereo cable that is thin and bendable. The wire will have a 1/8-inch stereo plug formed onto it already, which is a plus!
Rolling a razor blade very carefully over the insulation without cutting the wire underneath is the best way to go when stripping that type of wire. Very carefully pull the insulation away from the wire once it is cut. Teflon-insulated wire does very well with this technique. Once the wire is prepped, mark the wire that is attached to the ring and the one that goes to the tip of the jack. Using an ohmmeter makes it easier.
Cautiously fuse the wires to the microphone elements. The easiest way to do that is to pre-tin the wires and melt the little spot of solder on the microphone part with the tinned wire below the soldering iron tip. Carefully look at the microphone. The terminal that is connected to the case of the microphone is the ground connection. The other terminal is the actual microphone output. To make this a lot easier, hold the microphone element in an alligator-clip holder. When finished fusing the microphone elements, it is smart to test them before gluing them to the headphones.
One way to get the microphones attached to the headphones is to use a bit of silicone sealant. Using a toothpick or the like, shape the silicone around the edges of the microphone elements to smooth everything off. Do not get any on the black felt surface that is where the sound enters. Attach the left and right microphones to the left and right sides of the headphones, correspondingly.
When the glue is no longer wet, collect and package the wires together with many nylon tie wraps along the length of the wires. Now that the headphones are complete, it is time to test the Noise-Canceling Headphones.