A perfectly good piezo electric pick-up can be made with a couple inexpensive items from Radio Shack. Here's how to do it:
First, go to Radio Shack and buy a #273-073A Piezo Transducer and a 1/4" panel-mount, mono, female phono jack. Solder the red wire from the transducer to the center pole, the black one to the outer (ground) pole of the jack:
That's it for the electronics! Test it by plugging it into an amp and tapping on it. Further test by placing it on the top of your uke and plucking the strings (hold it down so it doesn't rattle on the top). Cool, eh?
Next, plan where the two components are going to go inside the uke. Stick your finger inside and feel around for the bracing. You're after a unobstructed flat spot big enough for the transducer, preferably on the 1st string side near the bridge. Once you have located that spot, place the transducer there (on the outside) and make sure that the wires are long enough to go to where the jack will be on the end. (Maybe this should be done before soldering the wires, eh? (just in case the wires need to be made a bit longer...).
Now for the scary part - drill a hole in the side to mount the jack. Probably 3/8", but please verify that. Note that on most ukes there is probably a thicker end block in the middle of the end, and a standard panel-mount jack would not be long enough to work there! If you aren't comfortable doing this, please get somebody else (who is) to help!!
Stick a length of 1/4" wood dowel through the new hole so that you can see it through the sound hole. Slide the jack on to the dowel. If not a snug fit, wrap a piece of tape around the dowel.
Now pull the stick & jack out towards the hole, feeding the wires and the transducer along behind. Once the threads of the jack are visible, stick your thumbnail in the threads and pull it out as far as possible. Install the washer and nut that came with the jack and tighten it up snug.
Now position the transducer so that you'll be able to dab glue on it and press it up against the top where it goes. When satisfied that you can do that, mix up a little five-minute epoxy and do it.
Plan ahead! Be ready with a beer/cocktail & smokes as you'll be standing there holding the damn thing in place for five or ten minutes while the glue sets up. Poke at the left-over glue with your other hand from time to time to see how it's going.
You're done - plug it in and play!
Click here for a video sound sample.