Datasheet

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The resistor circuit symbols are usually enhanced with both a resistance value and a name. The value, displayed in ohms, is obviously critical for both evaluating and actually
constructing the circuit. The name of the resistor is usually an R preceding a number. Each resistor in a circuit should have a unique name/number. For example, here’s a few
resistors in action on a 555 timer circuit:
In this circuit, resistors play a key role in setting the frequency of the 555 timer’s output. Another resistor (R3) limits the current through an LED.
Types of Resistors
Resistors come in a variety of shapes and sizes. They might be through-hole or surface-mount. They might be a standard, static resistor, a pack of resistors, or a special
variable resistor.
Termination and mounting
Resistors will come in one of two termination-types: through-hole or surface-mount. These types of resistors are usually abbreviated as either PTH (plated through-hole) or
SMD/SMT (surface-mount technology or device).
Through-hole resistors come with long, pliable leads which can be stuck into a breadboard or hand-soldered into a prototyping board or printed circuit board (PCB). These
resistors are usually more useful in breadboarding, prototyping, or in any case where you’d rather not solder tiny, little 0.6mm-long SMD resistors. The long leads usually
require trimming, and these resistors are bound to take up much more space than their surface-mount counterparts.
The most common through-hole resistors come in an axial package. The size of an axial resistor is relative to its power rating. A common ½W resistor measures about 9.2mm
across, while a smaller ¼W resistor is about 6.3mm long.
A half-watt (½W) resistor (above) sized up to a quarter-watt (¼W).
Surface-mount resistors are usually tiny black rectangles, terminated on either side with even smaller, shiny, silver, conductive edges. These resistors are intended to sit on
top of PCBs, where they’re soldered onto mating landing pads. Because these resistors are so small, they’re usually set into place by a robot, and sent through an oven where
solder melts and holds them in place.
A tiny 0603 330Ω resistor hovering over shiny George Washington’s nose on top of a U.S. quarter.
SMD resistors come in standardized sizes; usually either 0805 (0.8mm long by 0.5mm wide), 0603, or 0402. They’re great for mass circuit-board-production, or in designs
where space is a precious commodity. They take a steady, precise hand to manually solder, though!
Resistor composition
Resistors can be constructed out of a variety of materials. Most common, modern resistors are made out of either a carbon, metal, or metal-oxide film. In these resistors, a
thin film of conductive (though still resistive) material is wrapped in a helix around and covered by an insulating material. Most of the standard, no-frills, through-hole resistors
will come in a carbon-film or metal-film composition.