Relative humidity measuring the total circuit diagram as shown. Using an 89C2051 microcontroller can drive four LED digital tube . TLC555 output square wave frequency signal through the amplification , shaping and opto- isolation circuit, given 89C2051 timer . Using the keyboard to complete the setup , measurement , or reset operation , the program stored in the 89C2051 on the ROM. The instruments measure relative humidity range is 0 to 100 % accuracy up to ± 2% RH, resolution is 0.01% RH.