Abstract: A latching circuit is used to exclusively select either a full intensity command signal, a presettable intermediate intensity command signal or a zero intensity command signal. The command signals are fed to an output signal generating circuit which controls a variable voltage supply source for a lighting system. A null comparator and integrating circuit compares the output signal with the selected command signal and increases or decreases the output signal until it is in conformity with the selected command signal. Circuits are also disclosed which provide the capability of changing the intensity of the lights between two preselected intermediate intensity levels or between any two of a number of preselected intermediate intensity levels.

Abstract: An enabling circuit selectively generates first, second and third enabling signals. The first enabling signal enables a pulse generator means which generates a train of clock pulses. The second enabling signal enables a gating means which applies the clock pulses generated by the pulse generator means to the up input terminal of an up/down counter. The third enabling signal enables a gating means which applies the clock pulses generated by the pulse generator means to the down input terminal of the up/down counter. The up/down counter evaluates the difference between the number of clock pulses applied to its up input terminal and the number of clock pulses applied to its down input terminal and generates a digital signal representative of the evaluation. Finally, digital to analog converter means generates an analog output control signal whose magnitude is determined by the digital generated by the up/down counter.