Here is a device that musicians will find
highly useful. It will detect breaks or shorts in a guitar or monitor cable.
Much more elaborate cable testers are available at music stores, but they are fairly
complex and are mostly useful to road crews and technicians. The musician doesn't
really care what is wrong with cable, only whether it's good or not. You can't beat
this tester for simplicity and ease of use. It is also extremely compact and can be
easily stored in a gig bag.
A two-transistor current regulator circuit
is used instead of a resistor to maximize battery life. Any general-purpose silicon
transistor can be used. The enclosure is Radio Shack P/N 270-1802. The 1/4
inch phone jacks (Radio Shack P/N 274-252 or Switchcraft P/N 11) are mounted as far apart
as possible to make room for the 9-volt battery. The tip contacts on the jack are
rotated inward to prevent the battery from interfering with plug insertion. The
regulator circuits is built on a tiny piece of perfboard tucked into a corner near the J1
connector (the one on the left). The regulator circuit is built on a tiny piece of
perfboard tucked into a corner near the back of the LED to keep them in place. Foam
padding is used to keep the battery from moving inside the box.