Abstract: A DC motor speed control circuit in which the current to the motor is delivered in a series of pulses the width of which is variable in accordance with the setting on a throttle control potentiometer. The pulses are shaped to provide a fast turn on and slow turn off of the control transistor to avoid heat build up and lessen the inductive kickback of the motor. A novel feedback circuit senses excessive current draw and automatically shuts down the circuit and remains latched in that condition until the throttle control potentiometer is reduced to zero whereupon the circuit automatically resets itself. High efficiency is achieved by directing both the power current and the control current through the motor windings thus increasing the battery life.

Abstract: A circuit to maintain the water level between low and high predetermined limits in a sump in which the signal from an upper limit probe operates a first lamp which illuminates a photo resistor controlling the gate of a triac. The triac turns on and enables a second lamp connected to a lower limit probe which illuminates the photo resistor and holds the triac on until the fluid level drops below the lower limit probe.

Abstract: A circuit for maintaining any medium between two predetermined limits, as for example, the water level in a sump. Current to drive the sump pump is gated through a programmable unijunction transistor which transistor is turned on by a signal from an upper limit probe in the sump which is activated by the water level reaching the probe position. When the transistor turns on it activates another portion of the circuit also utilizing programmable unijunction transistors which operates to turn off the first transistor in response to a signal from a lower limit probe positioned in the sump at a lower level. Silicon controlled rectifiers or transistor regenerative switch circuits may be substituted for the unijunction transistors.