Abstract: A musical pitch control for each of the strings on a musical instrument. A pivot arm is secured to one end of each string. Controlled current is applied to a length of memory wire secured between the arm and an anchor point. The bending strain on the arm is sensed and circuitry responsive to the sensor is arranged to rock the arm to maintain a desired tension on the string. A second biasing device also acts upon the arm in opposition to the alloy wire to urge the wire alloy to return to its original condition when no current is flowing through the memory wire.

Abstract: Automatic tuning control arrangement for a string musical instrument, such as a guitar, has a pivoted tone arm with a hook at one end for attaching to an associated one of the guitar strings, and a shape memory metal wire tension motor extending between the tone arm and an anchor point on the instrument to rock the tone arm in opposition to the tension of the musical string. A strain sensor, such as a strain gauge, is mounted on the tone arm and it is electrically coupled to a control circuit that supplies a control current to the shape memory metal wire in the traction motor. A biasing spring can also be coupled between the tone arm and a bias anchor on the instrument to apply a spring bias in opposition to the musical string tension. As the guitar string or other string stretches over time, the traction motor will rock the tone arm to take up the slack and maintain an even tension on the string, thus keeping the string in tune.