Browse Prior Art Database

Compensation of Liquid Crystal Display Contrast and Brightness for Temperature Variation

IP.com Disclosure Number: IPCOM000106275D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 99K

Publishing Venue

IBM

Related People

Keller, RJ: AUTHOR [+3]

Abstract

Disclosed is a method for controlling an (LCD) Liquid Crystal Display by means of a microprocessor to maintain essentially constant contrast and brightness despite variations in ambient temperature.

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This is the abbreviated version, containing approximately 52% of the total text.

Compensation of Liquid Crystal Display Contrast and Brightness for Temperature Variation

      Disclosed is a method for controlling an (LCD) Liquid Crystal
Display by means of a microprocessor to maintain essentially constant
contrast and brightness despite variations in ambient temperature.

      Under the direct control of a service processor, one side of a
dual digital potentiometer is used to set LCD contrast, while the
other side is used to set LCD brightness.  The user can adjust
contrast and brightness, providing inputs to the service processor by
means of binary switches.  An ambient temperature sensor measures the
temperature of the unit case below the LCD.  In Fig. 1, curve 1
indicates contrast potentiometer values which have been found to
produce optimum contrast in the LCD contrast circuit, as a function
of the temperatures shown along the horizontal axis.  These values
are given as hexadecimal numbers at the left scale of the graph,
ranging from E0 at 0degree C to 90 at 50degree C.  Each of the curves
2 shows the brightness obtained with the contrast potentiometer value
indicated adjacent to the curve, again as a function of temperature.
The relative brightness indicated by curves 2 is shown in the right
scale of the graph.

      The service processor uses a number of variables and flags
stored in on-board RAM.  The present contrast potentiometer value is
stored within the variable CPOT.  When the system is powered up, the
system processor sends a contrast potentiometer value to the service
processor, and the service processor adjusts this value to compensate
for the difference between the currently measured temperature and
25degree C.  Every time the user depresses switches to raise or lower
contrast, the service processor uses a contrast table to alter the
CPOT...