A basic sensor component can be thought of as an elementary electronic component that is used to measure electrical properties generated as a result of external stimuli on the component. An apt example of such a sensor would be electronic components such as photodiodes and thermistors. When external stimuli, such as light, heat, and moisture, act upon an elementary electronic component, then certain electrical responses are generated depending on the component and the stimuli. For example, temperature affects the resistance property of a thermistor. Similarly, when light is an incident upon a photodiode, it triggers the flow of current. In the first part of this chapter, we will learn how to measure the response generated in a photodiode and a photoresistor when light falls upon it.