3. Automatic Control of LCD ContrastThe control panel controller PCB is equipped with a mechanism capable ofautomatically adjusting the LCD contrast according to changes in temperature.A thermistor (TH911) is mounted on the control panel controller PCB to monitor thetemperature inside the control panel unit. The changes in the resistance of the thermistorcaused by changes in temperature are used to vary the voltage supplied to the LCDassembly to maintain a specific contrast of the LCD display at all times.The LCD contrast remains constant free of the influence of ambient temperatureonce it is set by the contrast adjusting knob on the control panel.Figure 7-103If the temperature around the control panel rises, the resistance of the thermistor willlower, thereby increasing the voltage (Vo) supplied to the LCD unit.If the temperature around the control panel lowers, on the other hand, the resistanceof the thermistor rises, thereby decreasing the voltage (Vo) supplied to the LCD unit.OV-24V+5VDC/DCConverterLCD unitThermistor(TH911)VR911VoVo: Voltage supplied to LCD unitCOPYRIGHT © 1997 CANON INC. CANON NP6350/NP6251 REV. 0 JULY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 7 EXTERNALS/AUXILIARY MECHANISMS7-4
