I am using a ADC0804 for measuring the voltage and displaying it on the LCD using 89v51.

All the connections of the ADC are done as shown in their sheet. The ADC is showing the '0' and 5 V correctly. however, in the middle of the voltage range the value is not correct. for eg. if the input is 3.53 V (as measured by digital voltmeter) my LCD is showing the voltage as 2.80 V. its moving up and down as desired but the values are off. The reference voltage is 2.44 V. If i put Vref to the input then it shows 2.44 correctly but any other value is off the mark.

Can somebody guide me with this problem......thanks

 

It sounds like you are loading down your voltage input being measured. Try adding a non-inverting buffer.

 

Thanks for the reply.....you mean add non-inverting buffer to the output lines of the ADC.

 

No, to the analog input of the ADC.