An analog-to-digital converter is a device which converts continuous signals to discrete digital numbers. Typically, an ADC is an electronic device that converts [[wysiwyg_imageupload::]]an input analog voltage (or current) to a digital number proportional to the magnitude of the voltage or current. This circuit demonstrates the interfacing of ADC0808 with 8051 microcontroller (AT89C51). The output is taken on the LEDs. This is an intermediate circuit, which finds lot of applications. ADC0808 needs an external clock to run. The circuit describes how a D-flip flop can be used to provide the external clock. Analog-to-digital converters are among the most widely used devices for data acquisition. Digital computers use binary values, but in physical world everything is analog. Therefore, we need an analog-to-digital converter to translate the analog signals to digital signals. An ADC has n-bit resolution where n can be 8,10,12,16 etc. The ADC chips are either parallel or serial. In parallel ADC we have 8 or more pins dedicated to bringing out the binary data. ADC0808 is a parallel ADC with 8-bit resolution.