lm35是测温传感器，每升1度，对应的电压就升10mV（这是该器件的特性）

该函数要求 每升0.5度，电压升5mV，并把温度显示在lcd1602上

即A/D转换的分辨率b为0.005v ，也就是温度传感器每0.5度，ADC0804就转换一次（电压-->温度）再去显示温度

这里还得到ds1802检测到的温度与lm35所得的电压进行比较，（在相同的环境温度应是相等）



分辨率b=5mV=VREF/256 所以VREF=1.28V

又因为ADC0802的9号引脚里有一个放大器（可放大为原来的2倍）

所以输入9号引脚的电压Vx=VREF/2=1.28/2=0.64V（可由电位器来控制）-lm35 is a temperature sensor, 1 degree per liter, corresponding to the voltage on the rise 10mV (which is the device' s characteristics) per liter, 0.5 degrees of the function required, the voltage rise 5mV, and the temperature is displayed in the lcd1602 on the A/D conversion resolution of b to 0.005v, which is the temperature sensor every 0.5 degrees, ADC0804 to convert a (voltage->　temperature) go here also show that the temperature detected by ds1802 lm35 temperature and voltage from comparing (in the same ambient temperature should be equal) resolution b = 5mV = VREF/256 so VREF = 1.28V and also because the 9-pin ADC0802 There is an amplifier (to enlarge the original 2-fold) so the input voltage Vx 9 pin = VREF/2 = 1.28/2 = 0.64V (by potentiometer to control)