12864液晶在出厂时其对比度已经调好，所以用户在使用的时候第三管脚可不用接任何东西，本实验板上为了兼容多家12864液晶所以加了液晶对比度调节电位器，若用户使用我们配套的12864液晶可不用管它，液晶的第三管脚悬空就可以。有些液晶功耗比较大，用户在使用的时候可将液晶的第19、20引脚的背光不接，这样字体会很清楚-12864 LCD contrast, when the factory has a good tune, so when users can not access the third pin anything, this experiment in order to compatible with more than 12,864 on-board LCD so the addition of LCD contrast adjustment potentiometer, if users supporting our 12864 can not regardless of LCD, LCD' s third pin can be left vacant. Some relatively large power consumption of LCD, users can be used when the first 19,20 LCD backlight will not receive the pin, so that fonts will be very clear