What Is A Resistor And What Does It Do?

The resistor is a component that resists the flow of current. It doesn’t do anything actively, so it’s called a passive component. Sounds boring and pretty useless, but it’s actually an extremely useful component. Once you know the basics of the resistor – and how it works with currents and voltages in a circuit –

The Pull-Up Resistor: How It Works and Choosing a Value

The pull-up resistor is very common and you’ll see it in digital circuits all the time. It’s just a resistor connected from an input up to VDD, the positive supply of the circuit.

For example on digital inputs on an Arduino. Or the input of digital chips such as the 4000-series IC.

Pull-up resistor example circuit

Pull-up resistors are used to make sure you have a HIGH state on the input pin when the button is not pushed. Without one, your input will be floating, and you risk that the input randomly changes between HIGH and LOW as it picks up noise in the air.

Is the current lower after a resistor?

Ohms law cartoon


It is not.

It’s a common misunderstanding.

But let me make it clear:

The current after a resistor is the exact same as it was before the resistor.

“But doesn’t the resistor reduce the current?”

How To Choose A Pull-up Resistor Value

I recently got a question about choosing a pull-up resistor value:

In Monostable button triggered circuit, why did you connect 10 kΩ specifically? Does it contain any calculations?

You can use resistors for many things. In the following 555 timer circuit that he was referring to, the resistor R2 is a pull-up resistor with a value of 10 kΩ:

Resistor Color Code Calculator and Table (4 and 5-band)

The resistor color code (color bands) on your resistor tells you what value the resistor has. There are usually 4 or 5 bands. Use our simple resistor color code calculator below to easily find the value of a resistor.

Select resistor type:
Value: 1000 Ω
Tolerance: 5 %

Click on a color band to change its color and see what the resulting value becomes.

Resistor Color Codes Table

You can find the color bands and the values they represent in the table below:

Further down this page, you’ll find examples of how to use the color table.

How to Create Your Own Resistor


Check out this simple tip that Michael sent me:

“I was making a small practice audio amplifier and was in need of a 2.5 Ohm resistor. I didn’t
have one and didn’t want to wait for an order to be fulfilled.

Current Limiting Resistor

A current limiting resistor is a resistor that is used to reduce the current in a circuit.

A simple example is a resistor in series with an LED.


You would usually want to have a current limiting resistor in series with your LED so that you can control the amount of current through the LED.

If too much current is going through your LED, it will burn out too fast. If too little current is going through it, it might not be enough to lit the LED.

Types of Resistors and How To Choose One

Did you know there are many types of resistors?

A mountain of different types of resistors

Your electronic schematic tells you that you need a resistor of 100k Ohms. Ok, so you go to an online store to buy one. But there you get all these choices: Thin film, carbon composition, metal film +++.

“Just give me a freaking 100k resistor man!”, you scream in despair.

Believe me, I know your frustration. It took me a long time to actually bother reading about different types of resistors. So I just chose random resistors for all my electronic circuits. Usually, it worked flawlessly. Maybe I was lucky or maybe I just didn’t identify the resistor as the problem when I had a problem.

Anyway, my aim here is to provide a simple guide on how to choose a resistor without diving deep into details.