Elektor Electronics 303 Circuits by Unknown

Author:Unknown
Language: eng
Format: epub

D4 . . . D68= LED red

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28-08-2008 10:07:05

Reminiscent of the accelerator pedal in a car, a swell pedal enables musicians to alter the sound volume by foot, since they invariably need both hands to play their instrument. Electronic organs have the swell pedal normally built into the front near the other pedals. Guitarists have to buy this almost indispensable aid for getting 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 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.

170

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, Ds, and a light-dependent resistor, LDR, protrude from the lid. A small sheet of metal or plastic, the underside of which is covered with white paper or cardboard, is then glued onto the foam rubber. The top of the metal or plastic sheet may be covered (glued) with a small rubber mat. When the foam rubber is compressed by foot pressure, the reflective white paper or cardboard comes nearer to the LED and LDR, which causes the resistance of the LDR to diminish. Because of the amplifying, inverting, and compensating action

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28-08-2008 10:07:42

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