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September 5, 2018

#1 Electronics: what’s that? — Resistors

Kondrat Kielar

Starting my series about electronics — let’s see what resistors are all about! Some of you probably have heard or even seen some resistors. I bet that most of you even used them — eg. by using a volume knob on your walkman (music player used by old people).

What is a resistor? It is an electrical part, which is used for limiting the current flow within a circuit. Right, I know it’s not so clear. Let’s have a look at the example.

Understanding it

Generally, physics of electronics are easily comparable to a flow of water. So what’s the best equivalent of a resistor in plumbing? In my opinion — a faucet. A faucet is an adjustable resistor which regulates the flow of water. The more you unscrew it, the more water flows through it. That’s what potentiometers are — adjustable resistors, our taps in the electrical world!

Have a look at the picture below. Here we can see a variety of potentiometers. If you look closely, then you will notice that every potentiometer has a rotatable (usually with a screwdriver) part. This is used for adjusting the resistance

Types of potentiometers

I wanted to write it without science talk, believe me!

As we are already familiar with the idea of what a resistor does, let’s come back to definitions. The ability to limit current that flows through the component is measured in ohms. The more ohms, the harder way for current to flow. Resistors are turning part of an electrical current flowing through it into heat. So apart from choosing the resistor by its resistance (ohms), you should also consider how much power (W) it can turn into heat without burning up. This parameter is called the power rating.

Fixed value resistors

Usually, we don’t need an adjustable resistor. Instead of a potentiometer, we can use a fixed value resistor. These have a pre-set resistance, that cannot be changed.

Fixed resistors also come in a few shapes and forms.

Resistors can take many forms!

Color coding

For sure you’ve noticed the colorful stripes on a carbon resistor. These stripes are here on purpose. By reading the color of each stripe you can say what’s the value of a resistor without using the ohmmeter. In my opinion, a multimeter is more convenient, but let’s have a look at the example.

Resistor color code

By reading bars from right to left, you will find values for:
- tolerance
- multiplier
- 3rd digit (can be omitted)
- 2nd digit
- 1st digit

Why reading from right to left? It’s so you won’t misinterpret the multiplier strip as the 3rd digit of value. So:

430*10= 4300 ohm = 4.3 kOhm!

That was easy, right? Of course, you are not the only one thinking that remembering all of these colors and values is a no-go. So a bunch of great people came up with an idea of a resistor color code calculators. You can find it here.

Also, check out AppStore and Google Play for some awesome apps doing the same thing. They may also be handier.

SMD components, as well as reading their values, will be covered in another blog post of this series. Stay tuned!

So we’ve got potentiometers and fixed value resistors. These are the most widely used types of components, which regulate resistance.

How about other types?

Of course, the resistors I’ve mentioned are not the only ones used commonly in electronics. These are just the most popular. Let see what we got:

  • Thermistors — resistance changes due to temperature
  • Photoresistors — change their resistance depending on lighting conditions
  • Varistors — change their resistance depending on the voltage

Symbols

Drawing resistor in your electrical circuit is quite simple:

a) fixed value resistor, b) variable value resistor, c) potentiometer

When you use “European” notation, then you should draw resistors as boxes:

a) fixed value resistor, b) variable resistor, c) potentiometer

Usage in IoT

As mentioned in the intro, each article will end with some examples of usage in IoT!

So, what can I do with resistors in my IoT device?

  • Knobs — if your device needs to adjust values on user input(eg. Volume, brightness), then a potentiometer can be helpful
  • Light detection — Want to be notified when a drawer is opened? Maybe you’ve got automatic window blinds which should open on sunrise? We’ve got photo resistors!
  • Temperature measurement — whenever you need to adjust home heating or do some telemetry, thermistors are the way to go!
  • Heating — as mentioned earlier, resistors turn power into heat. But be careful, it can be dangerous!
  • LEDs — EVERY LED should be connected along with proper resistor 😉

What’s next?

So now you are familiar with the basic types of resistors, their characteristics, symbols and finally — with their usage in IoT!
I hope this article will be your entry point to fascinating electronics world and you will come back for next articles in my “Electronics: what’s that?” series.

Kondrat Kielar is a Software Developer at inFullMobile, an international digital product design and development studio based in Warsaw, Poland.

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#1 Electronics: what’s that? — Resistors was originally published in inFullMobile Blog on Medium, where people are continuing the conversation by highlighting and responding to this story.

Written by
Kondrat Kielar

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