Voltage indicator using serial comparison voltage measurement

Abstract

A voltage indicator using a serial or sequential comparison voltage measurement technique. Reference voltages generated by a voltage divider are applied to inputs of a multiplexer which is driven by a counter to select one reference voltage at a time in sequence to be presented via an output terminal to one input of a voltage comparator. An input signal to be measured is applied the other input of the comparator. When the input signal matches or exceeds the reference voltage at the output terminal of the multiplexer, the comparator switches, providing an enable signal to a one-of-N decoder. The one-of-N decoder is also driven by the counter, so that outputs of the decoder and corresponding inputs of the multiplexer are addressed simultaneously. The outputs of the one-of-N decoder are connected to LEDs which indicate the voltage level or magnitude. The voltage input signal may be applied via a conditioning amplifier that scales the input signal and an absolute value amplifier which provides an output in one polarity for comparison purposes. DC voltage polarity is detected and may be indicated by separate LEDs. Additionally, an AC/DC decode logic circuit may be provided to discern between AC and DC input voltages, and provide appropriate indication. While the preferred embodiment contemplates that both nominal AC and DC reference voltages may be provided by the same voltage divider, a gain control signal may be provided to change the gain of the absolute value amplifier by a ratio of .sqroot.2 so that the same reference values may be used for both AC and DC measurements.