A/D转换：读入电位器抽头处的电压值V0，并进行判断比较。当电压0V<V0<1V时，LED3点亮；当电压1V<V0<2V时，LED3、LED4点亮；电压2V<V0<3V时，LED3、LED4、LED5点亮；当电压3V<V0<4V时，LED3、LED4、LED5、LED6点亮；当电压4V<V0<5V时，LED3、LED4、LED5、LED6、LED7点亮。-A/D conversion: read into the potentiometer voltage at the tap V0, and to determine the comparison. LED3, LED4 light　voltage 2V <V0 <3V, LED3, LED4, LED5 light　when the voltage 3V <V0 <2V, when the voltage is 3V <V0 < LED4, LED5, LED6 and LED6 are lit when the voltage is 4V <V0 <5V, and the LED3, LED4, LED5,