Abstract: Motor overload current is sensed and coupled to the input of an operational amplifier, causing the amplifier output to invert and charge a plurality of parallel connected capacitors. When the overload condition is present for a predetermined time, the capacitors are sufficiently charged to change the output state of a second operational amplifier. A diode is coupled between the output and the input of the second amplifier and is poled to latch the second amplifier into its inverted state when the capacitors have reached the predetermined charge. A luminous source, such as a light emitting diode, is coupled to the output of the second amplifier and becomes non-luminous in the inverted state of the second amplifier. The diode is photo-coupled to a photo conductive circuit for disabling the power coupling to the motor circuit when the diode is non-luminous.

Abstract: The control includes approach and safety mat switches to which are applied alternating current voltage. Each of the switches are coupled to respective high gain binary output, solid-state amplifiers which change state upon alternation of two different input voltages being compared. Upon closure of the approach mat switch, the corresponding binary amplifier is caused to change state which in turn changes the state and output signal of a third like amplifier. This output signal causes the energization of an electric motor which opens the door. Opening of the approach mat switch followed by closing of the safety mat switch, the corresponding amplifier changes state and holds the third amplifier in its state which causes energization of said motor, thereby holding the door open. A time delay circuit is connected to the third amplifier for delaying the change of state of the third amplifier after the approach and safety mat switches are opened.