Many applications need to measure and/or monitor the physical quantities like temperature, pressure, light intensity etc. The sensors used to measure the physical quantities give the output in analog form, which are converted to digital through an ADC for further processing. This circuit demonstrates the principle and operation of interfacing ADC0808 with three LDR. The output of the sensor is displayed on the LCD. The external clock needed by the ADC0808 is provided by the controller using interrupt. The output is displayed on the LCD. The circuit is divided into four parts: LDR, ADC, 8051 microcontroller and LCD. Its applications could be measuring and monitoring the light intensity level.