The dangers of learning electronics

Two weeks ago, we were instructed (as in most of the world these days) to self-isolate. My plans to fly down to Spain and build a kitchen had to be discarded.

But a wonderful thing happened instead:

I suddenly had time to build a new project!

My wife and I just moved into a new apartment in Oslo. We only need one bedroom, so I threw out the bed in the other room and replaced it with a desk.

Hello, workbench!

What do you need for a workbench? A power supply of course.

This has been brewing in the back of my head for a while.

But the other day, it occurred to me:

If there is one thing I’ve always had an abundance of in my life, it’s wall adapters.

You know, these wall plugs you use for your router, your radio, your phone charger +++

And as much as I’d love to use these for my projects, they never have the voltage I need.

So I decided to build an adapter for my adapters!

The idea is simple. The circuit takes a DC voltage input from any wall adapter. And I can adjust the output voltage to the voltage I need for whatever experiment I’m doing.

Now if you are an experienced circuit builder reading this you might think: “Hey, but something like that already exists. You can just buy a finished module”

But where’s the fun in that?

To me, building electronics isn’t about inventing some genius gadget that no one has thought about.

To me, it’s about being curious and experimenting. It’s about trying to solve problems. It’s about that inner voice that says “what if I did that”, then testing and seeing what happens.

When I do this, I’m in one of my happiest states. I forget to eat. And hours feel like minutes.

That’s what happened this week.

I was supposed to give myself half the day on Monday to work on this project.

Then I was supposed to stop and do other highly important tasks.

I failed.

It’s Wednesday now and I haven’t done anything other than work on the project.

That’s the danger of learning electronics.

I should probably add a warning on the Ohmify page: Electronics can be highly addictive. Do not join unless you are prepared to forget important things like eating.

I’ll post my progress on the project in the community forum of Ohmify. And I’ll add schematics and instructions for those interested in building the same project.

If you’re not a member yet, you can join here:
https://ohmify.com/join/

Keep On Soldering!

Oyvind @ build-electronic-circuits.com

Copyright Build Electronic Circuits

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How To Build An Automatic Night-Light

In this tutorial, you’ll learn how to build an automatic night-light that turns on when it gets dark. It’s a simple circuit that you can build on a breadboard.

This circuit shows you how to do it with an LED. But you can use the same principle to turn on bigger and brighter lights too.

Find the breadboard diagram and parts list below the video.

The Components You’ll Need

• 9V Battery
• Breadboard
• Photoresistor (around 5kΩ in light, 200kΩ or more in dark)
• Transistor BC547
• Resistor 100 kΩ
• Resistor 470 Ω
• Light-Emitting Diode (LED)

There are many ways to connect this circuit. I recommend using a breadboard since it’s quick and you can easily reuse components.

Below you can see how I connected this circuit on a breadboard:

How The Circuit Works

The photoresistor and the 100 kΩ resistor make up a voltage divider.

When there is a lot of light, the photoresistor will have low resistance, which means the voltage divider gives a low output voltage. So the transistor is off and cuts off the current to the LED. Which means no light.

When it’s dark, the photoresistor will have high resistance. That means the voltage divider gives a high output voltage which turns on the transistor. That means the LED is also on and will light up.

What Are the Voltages out From the Voltage Divider?

When it’s light and the photoresistor value is low, the output from the voltage divider is around 0.5V, which is not enough to turn on the transistor.

When it’s dark and the photoresistor value is high, the output from an unconnected voltage divider would be around 4.5V.

But since the output of the voltage divider is connected on the base of the transistor, the voltage will be limited by the forward voltage of the base-emitter connection (around 0.7V).

Questions?

Did you build this circuit? Do you have any questions about how it works or how to build it? Let me know in the comment section below.

Copyright Build Electronic Circuits

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Not sure how to build your idea? Here’s how:

“I know the basics, and I’ve built a few circuits. But I have no idea how the build my own ideas!”

That’s a common problem.

However, here’s how you solve it.

First of all, make your idea specific.

Choose ONE idea. And write down exactly what it is.

Let’s say it’s an internet-connected cat feeder that enables you to feed your cat while you’re at work.

The “internet-connected” part suggests that you need a microcontroller with an internet-connection. If you already have WiFi in your home, then the easiest way would be to find a microcontroller module with WiFi.

The cat-feeder part suggests that you need some kind of mechanism to release food into your cat’s bowl. To control this remotely, you need a motor.

And to be able to control the motor from the internet-connected microcontroller, you need a motor controller.

Now you’re starting to get an overview of what’s needed.

And before you go “Noooo! I don’t know how to do any of those things!” – realize that there is another step left:

Next up is the research phase.

You’re doing a project you haven’t done before. You’ll inevitably have to do some research!

Even professionals go through the research phase.

Read up on microcontroller modules with WiFi.

Read up on ideas for cat-feeder mechanisms.

Read up on motor controllers.

Take courses. Read books. Or search for articles on the internet.

And ask for help.

Here’s a tip on asking for help:

Don’t ask a general “How do I build an internet-connected cat-feeder?” question.

Because then it seems like you don’t want to put in the work yourself. And it’s demotivating to help people who don’t want to put in the work.

Instead ask for example: “I want to build an internet-connected cat-feeder, and I’m trying to figure out what I need. So far I think I need X,Y,Z – am I onto something here?.”

Or how about: “I’m working on an internet-connected cat-feeder, and I’ve been reading up on motor controllers. What I don’t understand is …”

Sometimes the act of asking helps you get clear and you’ll find the answer on your own.

Of course all of this becomes easier as you get more experience building projects. And as you understand more of the basics of electronics.

If you need a place to learn electronics from scratch and to get help with your projects, check out Ohmify. It’s were I spend my days teaching electronics and helping members make their dream projects come alive. More info here:

https://ohmify.com/join/

Keep On Soldering!
Oyvind @ build-electronic-circuits.com

Copyright Build Electronic Circuits

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What Is Electric Current?

Electric current is what you get when electric charge moves around a circuit. It’s pretty simple when you finally get it. But there are some common pitfalls that can give you the wrong idea when learning.

And if you don’t know what current is and how it works, it’s a huge source of confusion when learning electronics.

My goal is that after reading this article, you’ll understand what current is. And you’ll understand that a resistor must have the same amount of current going into it as going out from it.

The Current in a River Metaphor

Electric current is the movement of electric charge. It’s not the charge itself.

As a metaphor, you can think of a river. If a lot of water moves past a point in the river, it means the current is strong. If the water stands almost still, it means the current is weak.

(And if there’s no current at all, it doesn’t mean there’s no water, it just means that the water doesn’t move.)

The circles in the animation below represent electric charge. The current isn’t the circles, but the speed of the circles.

So if you look at the speed of the circles at any point, you’ll find the current at that point.

(I’ll touch upon the direction of current a bit further down.)

Electric Current Isn’t “Used up”

The battery’s voltage is what pushes the charges around the circuit. And here’s an extremely important fact:

A circuit is always completely filled with electric charges. Even when there’s no battery connected.

But when there’s no battery connected, they’re not moving – so there’s no current. But they are still there.

At the moment you connect the battery, the charges start flowing. And what’s very important to notice is that they start flowing in the whole circuit – not just at the start.

So you’ll have current everywhere in the circuit at the moment you connect the battery.

The battery always receives back what it pushes out. One charge pushed out of the plus terminal means one charge is pulled back in from the minus terminal.

That means that the current flowing out of the battery is exactly the same as the current flowing back into the battery.

Current is never “used up”.

How The Resistor Reduces Current

Let’s have a look at what this means for the resistor.

The resistor will “resist” the current. Meaning that it will slow down the charges flowing through it.

But since the circuit is completely filled with charges, that means the charges are slowed down in the whole circuit.

Just like when you squeeze a garden hose so that less water flows out of it. The water is slowed down in the whole hose, not just after the spot you squeeze.

So the current before the resistor is equal to the current after the resistor.

This means that in the case of using a resistor to protect an LED – it doesn’t matter if you place it before or after the LED. In both of the circuits below, the resistor protects the LED:

Electric Charges Don’t Accumulate Anywhere

Sometimes after explaining the above two circuits, I get this question:

“But Oyvind, what about in the beginning when you connect the battery? Before the charges have accumulated in the resistor, surely the LED will get a high current at first, right?”

No. The charges never accumulate anywhere in the circuit.

Remember that the circuit is always completely filled with charges. One charge pushed in means one charge pushed out.

This means that the current flowing out of the battery is the same as the current flowing into the battery, also at the exact moment you connect the battery.

The Direction of Current

In the animations above, the current flows from plus to minus. But you might have come across information saying the opposite – that current really flows from minus to plus. What’s correct?

Electrons flow the opposite way, from minus to plus. Electrons carry a negative charge and are the particles that usually move inside wires.

But current isn’t defined as the flow of electrons. It’s defined as the flow of charge.

The electron carries a charge. But there are other particles that carry charge in a circuit too. For example electron holes that move from plus to minus. And they can both exist in the same circuit.

Electrons are the most common particle that flow in an electric circuit. So shouldn’t we say the current flows from minus to plus?

Well, you can. But remember that electrons carry a negative charge. So you’ll end up with a negative current. Which is fine. You’ll get the same results as us who prefer the plus to minus direction.

Just know that in the world of electronics, an electric current of -20 mA flowing from minus to plus is the exact same thing as a current of +20 mA flowing from plus to minus.

Questions

After reading this, is it clear to you what electric current is? Do you have any questions? Let me know in the comment field below!

Copyright Build Electronic Circuits

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