In this post, I’ll give you an overview of the most basic electronic component – what is a resistor, types of resistors, the resistor color code and how a resistor works.
Even though the operation of a resistor is very basic, it is one of those essential components that is used in almost all electronic circuits. When building circuits even with easy development platforms like the Arduino, you’ll eventually need to use external resistors when you start attaching external components even for simple things like powering up LED’s where a pull up resistor is required.
What is a Resistor ?
A resistor is a component that does exactly what its name suggests. It resists electrical current. The amount of electric current slowed depends on the value of the resistance that is used. Resistance is measured in the unit called Ohm’s.
How a Resistor Works ?
A simple way to explain how a resistor works is using the water pipe analogy. A wire with an electrical current flowing through it can be viewed in a similar way that a pipe carries water.
Let’s say the pipe (wire) has zero resistance, if we were to restrict the diameter of the pipe at some point this is called a point of resistance which we can consider as the resistor in the circuit. So at this point of resistance the flow or current of water (or electrical current) is reduced and also the water pressure ( or electrical voltage) is reduced. This is how a resistor works by resisting the flow of electricity.
Types of resistor
At the heart of the resistor is a resistive component that comes in three common forms – carbon film, metal film and wire wound.
Type of Resistor – Carbon Film
The carbon film resistor is a film of carbon deposited around a solid ceramic cylinder. A helical cut is then made around the carbon film to set the resistance value. The color of the casing of a carbon film resistor is usually a light tan color. The tolerance of a carbon film resistor is 5% or 10% which means the resistance value can vary by up to 5% or 10%.
On the photo of the carbon film resistor below, I’ve chipped away some of the outer coating and you can see the helical carbon film as well as the outer metal caps that hold the resistor’s legs in place.
Type of Resistor – Metal Film
The metal film resistor is constructed in the same way as the carbon film resistor except the resistance component is metallic instead of carbon which makes the cost of production slightly higher. The advantage of using metal film is the tolerance is reduced to 1 or 2%. For most general circuits a carbon film resistor will do but if the circuit requires lower tolerance which means lower resistance variation then this is when a metal film resistor should be used. The casing of a metal film resistor is usually colored blue which can make the resistor colour code markings hard to read. Also having lower tolerance allows for a wider range of values to be produced compared to carbon film resistors.
You can see here as with the carbon film resistor, I’ve removed some of this metal film resistor’s outer coating and you can see the helical metal film along with the metal caps on each end of the resistor that holds the connecting legs in place.
Type of Resistor – Wire Wound
The third type is the Wire wound resistor (see photo below) used for circuits that have high current requirements, generally above 1W. These resistors are constructed using a ni-chrome wire. When these resistors are in use they can get quite hot as they need to dissipate a lot of power.
Resistor Power Ratings
Maximum power ratings of resistors vary in value from 1/8th to 1W for film type resistors and above 1W for wire wound resistors as they can tolerate much higher power absorption.
Resistor Color Code Chart – Resistor Bands
The value of a resistor is read using a resistor color chart like the chart in the image below. Carbon film resistors use 4 color bands to represent two significant values, a multiplier and a 4th band to represent the tolerance. Metal film resistors can use 4 or 5 color bands, the ones that use 5 resistor bands have a third significant value.
What is a Resistor, Types of Resistors, Resistor Color Code | Summary
That was brief look at the various types of resistor that are used for through-hole circuit boards and how they work. In a up coming post, we’ll look at ohm’s law and how to calculate resistor values required for some simple circuits.
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