A piezo transducer pickup is a fun and inexpensive way to record your acoustic guitar or even play it through an electric guitar amplifier to use effects like distortion and delay. The pickup is made out of a piezo buzzer element, which can be purchased at many electronics stores for as little as $3. The piezo buzzer's transducer element, when wired correctly, acts as a small microphone, transferring any sound made by your acoustic instrument into a usable electronic signal.
Carefully break open the piezo buzzer. Remove the round metal transducer element from inside the buzzer. This is what will act as your pickup or microphone.
Use wire strippers to remove the rubber shielding from the ends of a 1-foot shielded audio cable. You should see a red wire (the signal wire) and a black wire (the ground wire) on the inside of the cable's shielded casing.
Solder the signal wire (the red wire) to the center of the piezo buzzer transducer element. This is the part of the transducer that detects sound, so be careful not to bend, dent or otherwise harm the surface of the element.
Solder the ground wire (the black wire) to the outer brass surface of the transducer element. Be sure this wire and any solder used doesn't touch the inner surface of the transducer.
Solder the signal wire (the red wire) at the other end of your audio cable to the signal tab on a 1/4-inch audio jack. Solder the ground wire (the black wire) to the ground tab on the jack.
Plug a 1/4-inch guitar cable or other shielded audio cable into the 1/4-inch audio jack connected to the transducer element. Place the element inside an acoustic instrument through the sound hole. Plug into an amplifier or recorder and play away. If you've succeeded, you should hear the sound of your instrument through the amplifier.
The placement of your piezo transducer pickup has a great affect on the resulting sound of the instrument through the amp of your recorder. Experiment with different placements for the pickup to find the best sound for your instrument. When you find a setup you like, simply tape the pickup in place.