Keyboard pulse generator including a locking plate for use in telephone dialing

Claim 1

A telephone dialing system comprising a dialing panel having a plurality of successive pushbutton switches, means responsive to depression of a selected one of said switches for generating a pulse train having a number of pulses therein representative of the selected switch, means for shaping said pulses, a voltage source, relay means connected to said voltage source and responsive to the resulting shaped pulses for effecting a number of relay closures dependent upon the number of pulses in said train, and means for connecting the output of said relay means to a telephone line, wherein the pushbutton switches include actuators, a slidable plate mounting the actuators, camming means formed on the actuators to cooperate with the plate for displacing the plate in response to depression of an actuator, and means formed in the actuators for selectively contacting the plate in its displaced position thereby preventing depression of other actuators during the time said actuator remains depressed, the means formed in the actuators having a plurality of notches, and wherein the plate is spring-biased and has a plurality of apertures normally permitting free passage of an actuator therethrough, displacement of the plate causing said engagement between the notch of the depressed actuator and the wall of an associated aperture, latch means for maintaining the plate means in the displaced position, and reset means for retracting said latch means thereby returning the plate to an original biased position, the latch means comprising a solenoid for engaging an opening in the plate when the plate is displaced, said reset means including a pulse shaping circuit responsive to the last pulse of said pulse train, the solenoid being energizable by said shaping circuit to cause disengagement between the solenoid and the plate.