AVR: Low Cost A/D Converter

What is an ADC?
ADC stands for analog-to-digital converter. It is an electronic device that converts input analog voltage to a discrete digital number. Applications include anything that involves the processing of analog signals into digital form.

What does analog mean?
A continuously varying signal. For example, if an analog signal's range is from 0V to 5V, the signal can assume any voltage within that range such as 1.2, 2.4, or 4.7V. Microprocessors and microcontrollers usually cannot process analog signals directly and require conversion by an A/D converter before they can process the signal.