通过两个PIC引脚驱动六只LED灯

　　本设计实例展示了仅使用两条MCU的I/O口线驱动六只LED灯的新方法，这种方法尤其适用于任何引脚有限的芯片。这种方法使用了两条I/O口线以及一对互补双极型晶体管。通过多路复用的方法可点亮一只以上的LED灯。

　　图1:测试选择PIC10F200,固件以两个独立、简单的汇编程序源代码的方式提供。

　　注意：VDD必须在2V和3V之间。例如，如果LED2点亮（表1），那么在VDD过高的情况下，LED4和LED6也将被点亮。可以选择使用任何通用低功率晶体管，但如想使所有LED保持同样的亮度，则需选择低VCE（sat）的晶体管。

　　表1:LED驱动逻辑表。避免（0,0）和（1,1）。

　　测试选择了PIC10F200,因为PIC10F200是最小、最简单的六引脚MCU。出于示范目的，固件以两个独立、简单的汇编程序源代码的方式提供。

　　注意：在任何一种模式下，每次仅采用最小电流（高亮度LED低至2mA）及周期性短脉冲突发模式驱动一只LED灯。汇编程序源代码做了完整注释，优化了长度，不超过256个字，让用户可选择其他任何引脚有限的PIC。

　　参考文献：

　　[1]Decoder lights the way （EDN | February 19, 2009）

　　[2] Microcontroller drives logarithmic/linear dot/bar 20-LED display （EDN | January 18, 2007）

　　[3]Squeeze extra outputs from a pin-limited microcontroller （EDN | August 4, 2005）

　　[4]Microcontroller's single I/O-port line drives a bar-graph display （EDN | July 6, 2006）

　　[5] Drive 12 LEDs with one I/O line （EDN | February 4, 2010）

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