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Three State Indicating Circuit

IP.com Disclosure Number: IPCOM000086788D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR

Abstract

This indicating circuit 8 utilizes a (normally) two-color light-emitting diode (LED) 1C and a grounded single polarity power supply for definitely indicating three different machine operating states, as well as indicating a fourth state, by the absence of light.

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Three State Indicating Circuit

This indicating circuit 8 utilizes a (normally) two-color light-emitting diode (LED) 1C and a grounded single polarity power supply for definitely indicating three different machine operating states, as well as indicating a fourth state, by the absence of light.

A pair of input terminals 12 and 14, and a reference terminal 16, which preferably is at ground potential, are coupled to machine operating circuitry from which a modest positive potential (termed "high"), a low positive (close to zero) potential (termed "low") and a potential alternating between high and low are supplied.

High logic level voltages applied between the terminals 12-16 and 14-16 serve to open an AND gating circuit 18. This in turn will cause an NPN transistor 20 to turn on and to bring the lower terminal of a load resistor 22 effectively to ground. Current will then flow through resistor 24, a red light-emitting element R of LED 10 and the collector-emitter circuit of the transistor 20. The resistance value of resistor 24 is, at least, sufficiently large to limit the current through the diode element R to a value safe for this element.

Low logic level voltages applied at the terminals 12-16 and 14-16 serve to open a NOR gating circuit 26 and thereby turn on another PNP transistor 30. This brings the lower terminal of the other load resistor 24 effectively to ground, and current will then flow through the first load resistor 22, a green light emitting diode ele...