Published in the January, 1976 issue of Broadcast Management & Engineering Magazine

Problem: To use a single-pole momentary-contact pushbutton to remote-start cartridge machines and reset a common digital electronic clock in a situation where no ground or common bus can be used.

Solution: Series diodes are placed on both sides of the pushbutton switches in both the clock and cart machine circuits, with proper polarity to isolate the two circuits from each other. The clock floats with respect to ground because of it's internal power transformer. It makes no difference if either side of the cart machine circuitry sees a ground.

For simplicity, the clock re-set and the cart machines remote start circuits have been re-drawn with their equivalents. The circuit is easily understood when we realize that, with the switch open, no current flows in either circuit. When as button is pressed, current flows in both the clock and cart machine circuits independently. Since the two circuits are effectively coupled at only one point, there is no interaction between the two whatsoever. Any number of machines using any combination of direct current control voltages can be connected in this manner, and any number of buttons may be pressed simultaneously. KKDJ (now KIIS) employs a Heathkit GC-1005 digital clock inexpensively modified to re-set to zero, coupled to six ITC cart nachines, and controlled with touch switches.

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