Digital circuits are electronic devices that show either high or low operating states. Other ways of describing digital circuit operating states include true or false and binary 1 or 0. A Truth Table (TT), as discussed in the previous chapter, is a graphical tool used to test the electrical operation of digital circuits by showing input data and observing their output states. The TT aids the makers building digital circuits by allowing them to inject test data into the device's input pins and observing the output states using a logic probe.

A logic probe is an electrical tester that displays input and output signals of a digital circuit using visual indicators. LEDs are typical visual indicators used to show the binary data of a digital circuit. Typical colors used to represent high and low digital data are red and green, respectively. Some variations of logic probe visual indicator may consist of a seven segment display capable of displaying the letters...