Abstract: A flasher circuit for switching incandescent lamps with field effect transistor switches is described for use on a school bus. A current sensing resistor develops an actual load current signal and a current limiting circuit which generates a signal corresponding to a predetermined limit value of load current. A control circuit turns off the field effect transistor when the actual value of load current exceeds the predetermined value. A micro controller holds the reference voltage at a higher level during the inrush current interval and switches it to a lower level during the steady state current.

Abstract: A power actuated door opener is disclosed with a beam break system for detecting obstructions in a door opening. A transmitter includes a beam emitter and emitter drive circuit for transmitting a train of emitter pulses to a receiver. The receiver includes a pulse detector circuit with a beam detector for producing detector pulses in response to emitter pulses impinging on the detector. The emitter drive circuit and the pulse detector circuit are synchronously coupled with each other and the pulse detector circuit produces a normal output signal only if the detector receives a pulse which is in synchronism with an emitter pulse. The receiver includes an annunciator which produces an audible and a visible warning signal when the pulse detector circuit produces a fault output signal. The audible annunicator is a piezoelectric crystal mounted in the receiver housing with a cover plate operating as a sounding board.