A true classic for DIY synth makers & circuit benders, the Atari Punk Console can kick out some ear-catching square waves. It's easy to build and a lot of fun to play around with. It may be challenging to make traditional music with an APC, but hey - there's enough of that around already, right?
It's amazing what a little disk can do … when it's layered with piezoelectric crystals. Piezo disks are impressively sensitive to vibration and can easily be adapted to work as a contact microphones. The trick is the preamp - a basic circuit used to match the piezo's signal to levels compatible with modern audio gear inputs. The resulting piezo/preamp combo can be used for electrifying an acoustic guitar or simply exploring the lesser-heard world of small sound around us.
Infrared light may be invisible to the human eye - but it's usefulness in the world of electronics is easy to see. IR emitters & detectors can be used in a variety of different ways - most of us use them for wireless communication everyday.
Schematics are the functional diagram of electronic circuits. With so many designs available on the web, understanding how to read schematics can unlock a world of possibilities for the electronics maker. In fact, if you can read a schematic, you can build a circuit before even understanding how it works!