The reference design being shown is a simple temperature sensing circuit that uses LM35 as the sensing component and the ADC0804, which is the main component that digitalized the analog input. The ADC0804 is a CMOS 8-bit analog-to-digital converter that uses a differential potentiometric ladder. In this design, LM158 which is a two independent, high gain and internally frequency compensated general-purpose op-amp is used to be the one sending the reference voltage to the ADC0804. Read more