Introduction: Electronics for Dummies: Resistors
In this instructable you will learn:
What a resistor is
Different types of resistors
Resistor schematic symbols
How to calculate resistor values
Step 1: Schematic Symbol
Step 2: Definition
Resistors are used to regulate the amount of current flowing in a circuit - the higher the resistor's value or resistance, the less current flowing in a circuit and vice-versa. Resistor values are measured in ohm's (Ω) and are identified by the color band on their bodies. They may be connected into a circuit either way around as they are not polarised.
Resistors are made in different sizes, capable of dissipating or 'getting rid of ' different amounts of energy as heat.They are also made using different materials as the actual resistive element. Small low power resistors usually have an element made from either carbon or a thin film of metal. Larger resistors made to dissipate more power generally have an element wound from a wire such as nichrome (nickel-chromium-alloy)
A potentiometer (or pot) is basically a variable resistor. It has three terminals and is fitted with a rotary control shaft or spindle. Rotating its shaft varies the position of a wiping metal contact on a circular carbon resistance track inside the pot body, and this in turn determines the resistance between the wiper (centre terminal) and the two outer terminals. Potentiometers are commonly used as volume controls.
A trimpot is a special type of potentiometer which, while variable, is intended to be adjusted once or only occasionally. For this reason a control shaft is not included, but instead a slot or cross cutout is provided in the centre of the wiper rotor so it can be adjusted using a small screwdriver. Some trimpots are made with their total resistive element and wiper control exposed, while others are enclosed in a small plastic case.
Light Dependant Resistor:
A light dependant resistor (or LDR) is a special type of resistor that varies its resistance value according to the amount of light falling on it. When it is in the dark, an LDR will typically have a very high resistance (e.g. millions of ohms), but this will fall to just a few hundred ohms when the LDR is exposed to strong light. They are not polarised.
Step 3: Resistor Calculator
Also a good website for a calculator here