说明：  The optimal contrast setting for LCDs varies with ambient temperature. For most applications this variation in contrast is tolerable over the "normal" temperature range of 0℃ to +50℃. Most LCD modules are available with an extended temperature range option which allows the display to operate from -20℃ to +70℃. The changes in contrast are NOT usually tolerable over this wide range of temperatures, which means a way of adjusting the contrast voltage as the ambient temperature changes must be provided.