Abstract: Pulse techniques are used to periodically monitor a desired environmental condition, such as pressure. A solid-state switch is connected between a power source and a load. In the off state of the switch, power from the source drives a timer circuit which supplies a short voltage pulse to a circuit for sensing the environmental condition. At the same time, the pulse is supplied to associated circuitry for temperature compensation, amplification of the resulting sensing circuit signal, and a comparator circuit which determines whether or not a signal of the condition sensed exceeds a predetermined threshold. If such signal exceeds the threshold, the solid-state switch is turned on to connect the voltage source to the load. Turning on the switch results in substantially eliminating the voltage drop between the switch terminals, which previously was used to actuate the timer.

Abstract: An improved SCUBA diving gauge. A pictograph display is provided which has a shape which conveys the type of information being displayed. The pictograph has the shape of a SCUBA tank for a tank pressure display and the shape of a person for a display of nitrogen absorbed. Pressure transducers coupled to the SCUBA tank and the external water provide the pressure readings required to produce the respective displays. The differential signal from the transducer is supplied to a processor through an auto-zeroing circuit. The auto-zeroing circuit uses a capacitor initially coupled to an amplifier reference input and single ended output to store an offset voltage. During a measurement, the capacitor is disconnected from the amplifier output and has its other lead coupled to a full scale value of the differential input to produce an output signal which is a ratio.