Circuit for controlling the expression of an electronically controlled keyboard instrument

Abstract From the Canadian patent

There is disclosed a circuit for controlling the expression of an electronically controlled keyboard instrument which circuit works on the principle that by switching a solenoid on and off at a rapid rate and then varying the time on versus the time off the energy supplied, to the solenoid varies and therefore the striking force of the piano is changed. In accordance with the present invention, precise control over the width of the pulses is achieved by first setting a set voltage level and then adding thereto increments of set voltage according to a binary weighting. These voltages are then added and compared with a triangular voltage in a comparator. Both the up ramp portion and the down …