Intergrated Circuit - IC or chip
What they look like:
How they are shown on circuit diagrams
A 555 chip in a LED flasher circuit.
The numbers around the chip correspond to the leg numbers on the chip.
An Intergrated ircuit is just that .. an intergrated circuit. These small packages combine many individual components to perform a specific function. They vary in shape and size depending on their complexity. They are categorised into functions like Audio, Digital, Timers and many special functions. The limit is almost endless.
The anatomy of an IC
To explain further we will look specifically at the 555 timer chip.
The 555 IC is a universal timer used for many purposes and in the case above to flash LEDs on and off. With the help of a few external components, the 555 can precisely calculate time. How this is done is usually of no concern to electronics enthusiasts - as long as it works! However a basic overview may be interesting:
The figure below shows a functional block diagram of the 555. The dotted line is the chip with leg numbers shown. External components around the chip give flexability to the timer - a 5 minute timer would have different external components to a 30 minute timer.
FUNCTIONAL DIAGRAM OF A 555 IC
To make this all happen an engineer would sit down and construct a basic schematic for the chip:
SCHEMATIC DIAGRAM FOR THE 555 IC
So this small package, as small as our fingernail, is a combination of 23 transistors, 15 Resistors and 2 diodes.
How to identify them
Leg numbers follow a convention. The top of the chip is indicated by a circle or notch at the top. With the chip in this orientation, the top left pin in pin 1 - counting down to the bottom left pin then up the right side.
Chips have identifying markings on their surface. Amongst other characters, the chip number will be present. 555 in the case of the 555 chip.
Manufacturers print a logo or abbreviation on the chip some include:
Searching the manufacturers website will yeild data sheets for IC's you are using. These data sheets have all the information needed to use the chips - a sample data sheet :LM 555 Data Sheet