Time multiplexed control of air core gauges from a microprocessor

Abstract

An instrumentation system in which air core gauges are adapted for use with a microprocessor that provides data for the gauges in digital form via an address/data bus. One of the principal features of the invention is that minimum circuitry interfaces the microprocessor with the air core gauges. Each gauge is assigned to a particular output device on the microprocessor memory map. The microprocessor addresses a particular gauge via the address bus at the same time that data for the gauge is present on the data bus. Each gauge comprises a sample and hold circuit and an air core driver circuit which operate the gauge's air core meter. The sample and hold circuits share a common digital-to-analog (D/A) converter which is interposed between the digital data bus and the sample and hold circuits. A meter selection logic circuit receives address information from the microprocessor and causes the analog information from the D/A converter to be sampled and held by the particular gauge that is identified by the particular address being supplied to the meter selection logic. Each sample and hold circuit holds the information that has been multiplexed to it to thereby provide a continuous output signal to the associated driver circuit which in turn drives the air core meter movement to a corresponding deflection that indicates the value of the data that is in its sample and hold circuit.