Abstract: A circuit for determining whether a voltage is within a lower voltage range (+12 VDC) or a higher voltage range (+24 VDC) is provided. This circuit includes a resistor-based voltage-scaling circuit, a zener diode reference voltage circuit, and comparators for comparing the scaled voltages across the voltage-scaling circuit and zener diode circuit and for switching in response to the comparison outcome. The comparator output has a first state when the voltage is within acceptable limits in either the 12 VDC or 24 VDC range and a second state when the voltage is outside the acceptable range. Additional comparator circuitry switches the sensitivity of the resistor-scaling network between the 12 VDC and 24 VDC ranges.

Abstract: An engine status telemetry system includes engine parameter sensors, a transmitter, a receiver, and a display mechanism. The transmitter and receiver are time-division multiplexed such that the sensed parameter data is sent in time-serial channels from the transmitter and received and steered by the receiver in parallel format to the display mechanism. The transmitter and receiver are connected by a two-conductor link along which not only the multiplexed data is sent, but also along which the power to operate the receiver and display mechanism is sent. This minimizes the number of conductors which have to be run between the transmitter and receiver, or alternatively, between each of the transmitter and receiver and one or more power supplies. The engine status telemetry system further includes a circuit for determining whether the engine electrical system battery voltage and voltage regulator output voltage are within an acceptable voltage range regardless of whether the system is a 12 VDC or 24 VDC system.