swell pedal

Reminiscent of the accelerator pedal in a car, a swell pedal enables mu- sicians to alter the sound volume by foot, since they invariably need both hands to play their instrument. Elec- tronic organs have the swell pedal nor- mally built into the front near the other pedals. Guitarists have to buy this almost indispensable aid for get- ting the right blend of accompaniment and solo voice(s) as an optional extra. From an electronic point of view, such commercially available devices are simplicity itself: normally nothing 1 2 7-76 swell pedal 85486-1 470n more than a potentiometer operated by the foot pedal via a toothed bar. The mechanics, however, make home construction a rather more daunting task. The swell pedal described here avoids the mechanical intricacies. The circuit is entirely contained in a flat case of about the shoe-size of the user — see figure 1. A wedge-shaped, hollowed-out piece of foam rubber is glued onto the lid of the case. A light- emitting diode, D5, and a...