an automatic tuning system for a stringed instrument is formed by a microprocessor operating hardware connected with one end portion of the several strings . the hardware principally comprises a reversible motor driving gears and a gear train selectively meshed by a solenoid for each string entrained over a saddle at the bridge position and underlying a double hinged tremolo system . an input sensor in the tuning module detects the tone of a plucked string and converts it to a square wave of the detected frequency , which is compared by the microprocessor with the closest adjacent intended frequency and energizes the solenoid for engaging the gear mechanism for tightening or loosening the string to obtain the required frequency . the user can override the automatic string tuning function for initially tightening a string or strings , and manually adjust the frequency of a string by a manually rotated knob on the head stock of the instrument .