Automatic contrast adjusting device

Claim 2

The device as claimed in claim 1 wherein said characteristic correction means is responsive to a difference between a value set through said operation switch and a value set preceding the setting for changing a temperature range in which the contents of said characteristic table are to be corrected.

Claim 3

The device as claimed in claim 1 wherein said characteristic correction means corrects characteristic data only when an entry is not again made through said operation switch within a predetermined time after an entry through said operation switch terminates.

Claim 4

The device as claimed in claim 1 further including means for determining a liquid crystal display type, wherein the characteristic table in said storage means is provided for each liquid crystal display type and in response to the determination result of said determination means, the characteristic table corresponding to the determined liquid crystal display type is used.

Claim 5

In a liquid crystal display for displaying various items of information at a contrast in response to a given drive voltage, a device for automatically adjusting the contrast comprising: means for storing a characteristic table in which operating temperatures and drive voltages are related to each other; means for measuring temperature of said liquid crystal display; means being responsive to temperature data provided by said temperature measurement means for reading a drive voltage corresponding thereto from said characteristic table; and drive voltage output means being responsive to a difference between the drive voltage read by said read means and the preceding drive voltage for changing a correction amount of drive voltage supplied to said liquid crystal display and outputting the drive voltage.

Claim 6

The device as claimed in claim 2 wherein, when it is assumed that the correction amount of drive voltage set through said operation switch at temperature t is ΔV t , that the correction amounts of drive voltage at temperatures t-n-1 and t+n+1 are ΔV t-n-1 and ΔV t+n+1 respectively, and that α is a constant, said characteristic correction means corrects the characteristic table so as to satisfy an expression of ΔV t-n-1 = ΔV t+n+1 = ΔV t+n -α/ΔV t (n=0, 1, 2, ...)

Claim 7

The device as claimed in claim 1 wherein a contrast switch for increasing a drive voltage and a contrast switch for decreasing a drive voltage are provided as said operation switch and the drive voltage is related to a pulse width modulation pulse and wherein a duty ratio of the pulse width modulation pulse can be increased or decreased by depressing said contrast switch for increasing or decreasing the drive voltage in a one shot mode or continuously.

Claim 8

The device as claimed in claim 7 wherein, when said contrast switch is depressed continuously, the duty ratio of the pulse width modulation pulse is changed finely at the beginning, while it is changed coarsely as the depression time is prolonged.

Claim 9

The device as claimed in claim 1 wherein said temperature measurement means provides a temperature measurement value of said liquid crystal display by averaging a predetermined number of temperature sampling values.

Claim 10

The device as claimed in claim 4 wherein said storage means includes: a read-only memory which stores a characteristic table of temperatures vs. liquid crystal display drive voltages for each liquid crystal display type and from which when said liquid crystal display is first started, the characteristic table corresponding to the liquid crystal display type is read out; an electrically erasable programmable read-only memory which stores a characteristic table having been corrected and is read when said liquid crystal display is started at the second time or later; and a random access memory for working to store a characteristic table read from said read-only memory or said electrically erasable programmable read-only memory for correction by said characteristic correction means.

Claim 11

The device as claimed in claim 1 wherein said temperature measurement means comprises a thermistor.

Claim 12

In a liquid crystal display for displaying various pieces of information at a contrast in response to a given drive voltage, a device for automatically adjusting the contrast comprising: means for storing a characteristic table in which operating temperatures and drive voltages are related to each other; means for periodically measuring temperature of said liquid crystal display; means for comparing the current temperature data provided by said temperature measurement means with the preceding temperature data; and read means, when as a result of comparison by said comparison means, the current temperature data is less than the preceding temperature data, for decreasing a temperature variable when the characteristic table is referenced by a minimum step regardless of how much the difference therebetween is, or when the current temperature data is greater than the preceding temperature data, for increasing the temperature variable when the characteristic table is referenced by a minimum step only when the difference therebetween is a predetermined value or greater, and reading a drive voltage corresponding to the temperature variable from the characteristic table.