Browse Prior Art Database

Tri-Color LED Drive System

IP.com Disclosure Number: IPCOM000061047D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Buol, DA: AUTHOR [+2]

Abstract

A technique is described whereby a tri-color light-emitting diode (LED) is interfaced with a microprocessor controlled drive circuit so as to provide a low cost status indicator. The intent is to replace expensive displays, such as analog meters, incandescent lamps and analog or digital status monitoring devices. Commercially available tri-color LEDs have red and green light emitting diodes encased in a single holder with two operational leads. The LED emits a red light when a continuous voltage of one polarity is applied to the leads, a green light when the voltage polarity is reversed, and when the voltage polarity is switched rapidly, the eye averages the red and green colors so that the LED appears as yellow or orange.

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Tri-Color LED Drive System

A technique is described whereby a tri-color light-emitting diode (LED) is interfaced with a microprocessor controlled drive circuit so as to provide a low cost status indicator. The intent is to replace expensive displays, such as analog meters, incandescent lamps and analog or digital status monitoring devices. Commercially available tri-color LEDs have red and green light emitting diodes encased in a single holder with two operational leads. The LED emits a red light when a continuous voltage of one polarity is applied to the leads, a green light when the voltage polarity is reversed, and when the voltage polarity is switched rapidly, the eye averages the red and green colors so that the LED appears as yellow or orange. The technique described herein suggests the use of TTL (transistor-transistor logic) level drive signals and buffer drive circuitry to establish the red, green and yellow/orange colors when the proper indication is required. The buffer driver circuit module is one fourth of an octal buffer/line driver, 74LS244, as shown in Fig. 1, and uses two TTL level inputs A and B to control the on/off status and blink rate to LED 11. Enable line 12 can be used as a module select line, if inputs A and B are taken from a CPU bus. The timing charts in Fig. 2 illustrate four conditions to provide various colors at LED 11. By varying the duty cycle of the A and B inputs, all shades of colors between red and green will appear. The inte...