FIG. 1: With the MIDI jack in “smile” orientation, insert the cathode (short leg) of an LED in the second hole and the anode (long leg) in the fourth hole to make your playing shine. You can also identify the cathode by the flat spot on the LED''s collar.

For my 30th “Option-Click” column, I thought I''d share one of my favorite MIDI hacks: the one-bulb data detector. Simply plug an LED into the second and fourth holes in a MIDI out jack, and it will light up when the instrument transmits MIDI data. Actually, there''s a 50-percent chance it will light up because LEDs are unidirectional. Fig. 1 explains the necessary orientation. High-intensity LEDs work best. You can buy them for $1.49 at RadioShack, but it''s faster to cannibalize one of those ubiquitous keychain flashlights. For a more permanent installation, solder the LED into a MIDI plug—or even a plastic monster (see oreil.ly/MIDI-LED).