Why Resist?

Electric current is simply the motion of electrons from one place to another through a wire. The more electrons that are flowing, the higher the current.

Resistors have an apt name: They “resist” the electrical current going through them. You can think of resistors as “brakes” for electrons. By controlling the electrons going through a resistor, you can make a circuit do different things.

Resistors may be the primary building block of circuits, so you see them quite a bit in electronics projects. Here are some of the things you can use them for:

• Limiting current to another component: Some parts, such as light emitting diodes (LEDs), eat up current. Like a kid eats candy bars they try to gobble up as much as you give them. But LEDs run into a problem they burn themselves out if they eat too much current. You can use a resistor to limit the amount of current that reaches an LED.

• Reducing voltage to part of the circuit: In many circuits, you need to provide different voltages to different parts of the circuit. You can do this easily with resistors. Two resistors joined, as Figure 4-1 shows you, form what’s called a voltage divider. Assuming that you have two identical resistors, that is, they apply their brakes in the same amount, the voltage in between the two is exactly half that of the rest of the circuit.

• Controlling the voltage/current going into another component: Combine a resistor and a capacitor, for example, and you create a kind of hourglass timer. Or put a resistor at the input of a transistor to control how much the transistor amplifies a signal. Or . . . well, you get the idea.

• Protecting the inputs of sensitive components: Too much current destroys electronic components. By putting a resistor at the input of a sensitive transistor or integrated circuit, you limit the current that reaches that transistor or circuit. Although not foolproof, this simple technique can save you a lot of time and money that you would lose fixing accidental blow-ups of your circuits.

Types of Resistors

Resistors can come up in various types and sizes:

Fixed resistors

Resistors with a fixed ohmic value are (Obviously!) called fixed resisters. They are the most common and they come in different sizes depending on the power handling. Usually the bigger the resister in physical size the more power it can handle.

 

Various shapes of Fixed Resistors

Fixed Resistor Symbol

Variable resistors (Potentiometer)

These resistors come in a round shape housing with a dial that can be changed manually. The value of the resistor can be increased or decreased by turning the dial clock or counter clock wise. The most common application is the volume control of a speaker. Potentiometers come in two types:

• Linear where the resistance varies directly with the rotation of the dial.
• exponential :resistance varies exponentially with the rotation of the dial

Variable Resistor

How Variable Resistor Works

Variable resistor Symbol

Resistors Colour Code

Every resistor has its value either written in plain English or coded using colour codes. Colours on the resistor can be interpreted using the following table:

 

How I memorized the colour code sequence

I always had trouble remembering the sequence of colours , once a friend of mine gave me a phrase (Translators! please note that this is valid only in English) to help me recall the colours sequence: