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LEDs & Diodes

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Welcome to the lesson on LEDs and diodes.

In order to understand what an LED is we first need to take a look at what a diode is.

A diode is a simple device that allows for current to flow in only one direction.


The anode, the positive end has a higher positive potential than the cathode which is the negative end, also known as the LESS positive end.


This is called a forward based diode.


If the negative end had more potential it would be called a reverse biased diode.


This is what a diode looks like:




A basic diode has two layers of material.

One layer is doped with a more positive charge, the other with a more negative charge.

If there is a mark or stripe on one end it is the cathode, the more negative side, and should be connected to your power source appropriately in order for it to work properly.


Otherwise, you may permanently damage it.


The good news is they are cheap much like every other basic component, so make sure you always have a few available.

Here is the schematic symbol for a simple diode, it's so dope..:

P-type is the positively doped end and the N-type is the negatively doped end.


Remember, anode means positive connection to power and cathode means less positive (negative) end.

Diodes generally come in a tubular shape while some may be rectangular.

In order to understand how this works, we need to look at this diagram and make an analogy.


Think of it as a room with a wall in the middle.


In the positive room there are many orange colored balls inside and a few blue ones mixed in.


In the less positive, more negative side there are more blue colored balls with a few orange ones mixed in.


These rooms are under pressure so the balls are all being pushed against the center wall on each side.


Now imagine a few holes in that wall.


If we connect a vacuum hose at each far end of the rooms that sucks air from the positive orange ball room to the less positive blue ball room we allow a path for them to travel through in one direction.


So, we flip the switch on our vacuum and the balls pass through the holes in the wall to the blue side and the balls which leave the room through and loop back to our power source at the bottom.

Remember, it is just moving in ONE DIRECTION.

Current Flow.png

Current Flows This Way

If we flip the power source around by connecting the positive end to the negative end of the diode and the negative end of the power source to the positive end of the diode we are now blocking current flow instead of encouraging it.


Imagine our example is now flipped, look at the diagram below.

See how the positive orange end is on the negative side.


The balls are now being sucked out toward the far ends of the room with none touching the center wall.

You can also think of it as positive power attracting negative balloons on the left and negative power attracting positive balloons on the right.


Our vacuum has changed into an air pump trying to push the air through but the balls on the walls are resisting that flow.

This is just a way to interpret what is happening.

A much simpler way is to think of a diode as a water nozzle.

The water can't go back in the nozzle, it only shoots out in one direction.

You don't need to understand what is happening you just need to understand HOW to use the components.

Don't let others bully you about this fact.

They can flip through their text books all day while you will be busy building your kingdom.

Current Flow blocked.png

No Flow...Sadface

Take a minute to think this example over in your head.


The excitement and your power come when you start to understand these simple yet difficult concepts.

You WILL understand, just give yourself some time and have patience.


If you don't get it now, put it down, take a walk, wash some dishes, play some music then come back.

Diodes have several uses including converting AC to DC current, and preventing voltage spikes or sudden reverse voltage which can damage components such as when you stop supplying dc current to a motor.


As you probably guessed diodes come in many different flavors depending upon their ability to handle different rates of frequency and voltage.

One of the most common types of diodes found everywhere  is an LED.


LED stands for light emitting diode.

It is extremely efficient leaving it vulnerable to excessive voltage or current which can burn it out which is why you should play around with connecting different resistors connected to your LEDs to prolong their life and adjust their brightness.


Don't feel bad if you burn through some especially the tiny ones which operate on less than 3v of power.


My advice is to stock up on single LEDs.


They are extremely cheap and some can even change color with the use of Pulse Width Modulation which we will cover later.


Behold, the LED kingdom in all its glory.


Another commonly used diode is a photo sensitive diode which is really fun to play with as it adjusts its ability to pass current through itself depending upon the light being shone on it.


You probably can imagine how this can be used to automatically turn on street lights and their brightness according to how dark or light it is outside.


But we will work with photosensitive diodes later on.


Here is what they look like and the schematic symbol.


The arrows represent incoming light.


Pretty simple, huh ?


Here is the diagram of a basic LED. You don't have to understand all of it.


Just be familiar how it is a diode.


Pop Quiz

​1.  What is a diode?

2. What is the schematic for one?

3.  Why are diodes useful for motors?

4. Why is an LED a diode?

5.  What is the schematic of a photosensitive diode and how are they useful?

Get my favorite books on programming AVR chips I use.

Equip yourself with the most dependable, no hassle, quality usb programmer I use daily.

Make sure you have a basic kit. Arduino is fine, it contains the removable AVR 328p chip we will use.


I started with something very similar.


You now know what a diode is and its basic operation.

You learned the most common and useful form of a diode is an LED and that it stands for light emitting diode.

You know how to hook one up to a power source and what to expect.

Diodes will play an important role to prevent damage to important, more expensive components such as DC motors which can be damaged when the power source is cut off and the polarity reverses in them.

Study the diagrams and play with a few LEDs while trying to understand what is happening under the hood.

See you in the next lesson!

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