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. 相关型号   APP 3658: Nov 23, 2005 MAX4232 高输出驱动、10MHz、10V/µs、满摆幅输入/输出运算放大器，带有关断，SC70封装 完整的数据资料 (PDF, 1.3MB) 免费样品 MAX518 2线接口、串行、8位DAC，满摆幅输出 完整的数据资料 (PDF, 1.2MB) 免费样品 MAX7300 2线接口、2.5V至5.5V、20端口或28端口输入/输出扩展器 完整的数据资料 (PDF, 1.2MB) 免费样品 自动更新 需要自动接收最新发布的应用笔记吗？请订阅EE-Mail™ (English only)。 我们期待您的反馈！ 喜欢？不喜欢？有待改善？或为我们提供建议？请与我们联系 — 我们将根据您的意见或建议改善我们的工作。 网页评价或提供建议   下载，PDF格式 (70kB)  AN3658, AN 3658, APP3658, Appnote3658, Appnote 3658