Electromagnetically operated tuning key for piano - has electronic detector stopping further adjustment when note sounded by tuned wire matches reference frequency

摘要

A shaft with a screwdriver blade is inserted in the slot at the top of the piano wire tensioning screw. The shaft is held in the centre of a toothed wheel within a handle. The wheel is locked to the handle by a spring-loaded pawl. Attached to the pawl is a permanent magnet in the field of an electromagnet. The tuner first sets the tuning screw to achieve approximately the correct frequency. The electronic circuit then compares the note emitted by the wire with a reference frequency. When the two frequencies are identical, the pawl is withdrawn from the wheel preventing further adjustment. The electromagnet can be overridden by a manual pressure rod.