Many applications need to measure and/or monitor the physical quantities like temperature, pressure, light intensity etc. The sensors used to measure the physical [[wysiwyg_imageupload::]]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. ADC0808 is an 8-bit resolution ADC with eight input channels. At any point of time only one input can be read. The output of LDRs are used as inputs. An LDR will detect the intensity of light and generate voltage depending upon light intensity. A clock of frequency 500 KHz is generated using Timer0 in the interrupt mode. To enable the interrupt, the value of the register IE is set to 0x82.