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==Digital Circuits==
Unlike analogue circuits, elements in digital logic circuits are in states of either "high" or "low" (usually corresponding to "true" and "false", or "1" and "0").  In most cases, highs and lows are exhibited as voltage levels on the input and output pins of the integrated circuit.  Depending on the technology, this voltage level will vary.  

For Transistor-Transistor Logic (TTL) circuits, which is the most popular kind used in electronic projects, ''high'' is anything above 2V, and ''low'' is anything below 0.7V.  In these circuits, it is very common to use +5V for ''high'' and ground for ''low.''  If a pin is not connected (neither connected to the ''high'' voltage nor grounded), then it is '''floating'''.  TTL chips usually go ''high'' by themselves when floating, but don't count on it.  Inputs should never be floating; always have them connected to something.

[[Image:DIP_package.jpg|right|thumb|A DIP-14]]  Integrated circuits come in different '''packages'''.  The package refers to the type of exterior casing that the connects the actual integrated circuit chip to its input and output pins.  A common type of package is the ''Dual-In-Line Package'', or DIP.  This package contains a rectangular box with two rows of pins coming out of the long edge.  The number the succeeds "DIP" denotes the number of pins in package.  The package will often have an indentation or dot at one end to help identify the pins.

==Terminology==
===Active Low Input===
An '''active low''' input means that it is "on" when in input is low, and "off" when the input is high.  In schematic diagrams, it is often denoted by a "bubble" at the input pin.

===High===
''High'' usually corresponds to the binary "1," the "on" state, and "true" or "1" in Boolean logic.

===Low===
''Low'' usually corresponds to the binary "0," the "off" sate, and "false" or "0" in Boolean logic.