Abstract: Besides reducing the number of required GPIO lines from eleven to two, this circuit also provides programmable contrast and backlight control. Most LCD character displays connect to the outside world through a controller IC, such as the HD44780 (Hitachi) or equivalent. That interface has serious drawbacks, however. It uses up a large number of the microcontroller's general-purpose input/output (GPIO) pins, and it isn't capable of providing digital-contrast or backlight-intensity control. The circuit in Figure 1 reduces the required number of GPIOs from eleven to two, and also provides digital control of the LCD's contrast and backlight intensity. A versatile I/O-port expander (U1) emulates the typical 8-bit I/O port of a microcontroller. You can implement this interface with little or no extra code if your microcontroller integrates an I²C‡ peripheral. As an alternative, you can bit-bang the required signals through the regular GPIO pins. Figure 1. Besides reducing the number of required GPIO lines from eleven to two, this circuit also provides programmable contrast and backlight control. Op amp U3B buffers DAC output OUT1, which controls the contrast voltage. DAC output OUT0 controls a constant-current sink consisting of op amp U3A, MOSFET N1, and resistors R1, R5, and R6. This current sink draws 500mA when the DAC voltage output is at full scale. You might need to adjust the maximum LED backlight current according to the size of the LCD display. To do that, use the following equations to calculate resistor values R1, R5, and R6: where VDD(min) = minimum anode supply voltage (4.5V typ), VFLED(max) = maximum forward LED voltage, IFLED(max) = maximum forward LED current, RDS(ON) = on-resistance of switch N1, VFS(DAC) = full-scale voltage output of DAC, PR1 = minimum power rating of resistor R1, and R6 = 10kΩ. This application note appeared as a design idea in the June 9, 2005 issue of Electronic Design magazine. ‡Purchase of I²C components from Maxim Integrated Products, Inc., or one of its sublicensed Associate Companies, conveys a license under the Philips I²C Patent Rights to use these components in an I²C system, provided that the system conforms to the I²C Standard Specification defined by Philips. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 3658: Nov 23, 2005 MAX4232 SC70 패키지로 제공되며 셧다운 기능이 있는 고출력 구동, 10MHz, 10V/µs, Rail-to-Rail I/O Op 앰프 전체 데이터 시트 (PDF, 1MB) 무료 샘플 MAX518 Rail-to-Rail 출력이 내장된 2-Wire, 직렬 8비트 DAC 전체 데이터 시트 (PDF, 1.2MB) 무료 샘플 MAX7300 2-Wire 인터페이스, 2.5V ~ 5.5V, 20포트 또는 28포트 I/O 익스팬더 전체 데이터 시트 (PDF, 1.2MB) 무료 샘플   다운로드, PDF 형식 (68kB)  AN3658, AN 3658, APP3658, Appnote3658, Appnote 3658