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MOTOROLA INC. Technical Developments Volume 15
May 1992
TRANSMIT/RECEIVE INDICATOR IN BACKLIT LCD
by William Mark Bradford and Peter Bradford Gilmore
Motorola portable and mobile communications prod- ucts typically have a transmit/receive indicator. Many products have bi-color Light Emitting Diode's (LED's) which are normally off, but glow red on transmit and green on receive.
Control s&faces of portable products are becoming more and more crowded with critical customer features. The invention reduces the visual clutter of distinct items on the top of the radio, while retaining full function to the user. Liquid Crystal Displays (LCD's) are now com- mon on portable products. These displays are typically back-lit via one or more discrete LED's to allow the display to be used in the dark. The invention uses these back-light LED's as a transmit/receive indicator.
In a typical implementation, a portable radio with a top LCD would have four bi-color LED's surrounding a light-pipe to provide illumination for the LCD. These LED's are normally off. When the radio goes into trans- mit mode, one or more of the LED's would turn on and glow red. In receive mode, the LED would glow green. This red or green illumination would be guided by the light-pipe, and the LCD viewing window would glow with the appropriate color. The brightness could be con- trolled by the number of LED's turned on simultaneously. Normal back-lighting would occur by turning on the
LED's in bi-color mode (...
