INTRODUCTION TO ELECTRONICS

While we don’t intend this to be a complete textbook on electricity and circuits, there are some basic concepts you will want/need to understand to help you on your path of creating and programming electronics. The information below should be enough to get you started, but as you gain some experience building circuits, you’ll no doubt find that you have more questions and will be ready for more in-depth discussion of the topic. We highly recommend continuing to research any specific topics you're interested in using your favorite online search engine.

What is Electricity

Simply stated, electricity is a flow of charged particles (electrons). When charged particles are allowed to flow from one place to another, they transfer energy that can be used to power everything from a light bulb to an entire city. All of our everyday electronic gadgets – from cell phones to computers to microwave ovens – are powered by the flow of these charged particles, which we commonly refer to as electricity or simply just "charge."

What is a Circuit

A circuit is a closed loop that allows charged particles to flow through it.  The parts of a circuit that charged particles flow through is called conductors -- conductors are the building blocks of circuits, and wires are one example of a conductor.  Wires and other conductors allow charged particles to flow through them and when you string together conductors in a closed loop, you have created an electric circuit.

A typical circuit has a power source (something that provides the charged particles), conductors and various components that do stuff when electricity passes through them. For example, a circuit may contain a battery and a lightbulb, attached together with wires. The battery serves as the power source, the wires are the conductors that carry the charged particles and the lightbulb uses the charged particles to illuminate and provide light.

Some circuits are very simple (like our battery and lightbulb example), while other circuits are very complicated, containing many power sources, many conductors and many components.

Voltage, Current & Resistance

When discussing electricity and circuits, there are three major components that are important to understand:

  1. Voltage

  2. Current

  3. Resistance

These three things define how and when electric charge flows, and controlling these things allows us to harness the power that electricity provides. While we can’t actually see voltage, current or resistance, there are some analogies we can use to help understand what each of these things are and how each of these components interacts with the others.

Remember how we said that electricity is a flow of charged particles. Well, electricity through wire (or any conductor) is very similar, in principle, to how water flows through pipes. In fact, to understand the basic components of electricity – voltage, current and resistance – we’re going to use water flowing through pipes as our analogy.

Voltage

Voltage is essentially the difference in the amount of charge from one point in a circuit to another. An important concept of electricity is that charge will typically only flow between two points that have a difference in charge (a voltage).  Specifically, charged particles likes to flow from a point of higher charge to a point of lower charge. If there is the same amount of charge at two points in a circuit, no electricity will flow.

Using our water analogy, voltage is equivalent to the amount of pressure there is pushing water through a pipe.  Imagine a water system that contains a water pump -- water enters the pump at a low pressure and is ejected from the pump at a high pressure.  It is this pressure difference on either side of the pump that generates the flow of water.  Likewise in a circuit, the power source serves as the pump -- a power source takes in charge at a low voltage and pushes it out at a high voltage.  It is this difference in voltage on the opposite sides of of the power source that generates the flow of charged particles.

Before we go any further, let’s take a quick look at how a battery works. In a battery, there are two “terminals” – a positive terminal and a negative terminal. The positive terminal contains a lot of positively charged particles and the negative terminal contains a lot of negatively charged particles:

The difference in charge between the positive and negative terminals creates a voltage, but there is a barrier between the two terminals which keeps the positively charged particles and the negatively charged particles from mixing together.  But, if we were to place a conductor (like a wire) between the positive terminal and the negative terminal, charged particles would flow from one side to the other:

In fact, what you see above is what a typical battery-operated electric circuit will look like before you insert various components into the circuit loop. We could easily insert a lightbulb into the circuit above and you would see the lightbulb illuminate:

Keep this particular circuit in mind, as we’ll be coming back to it often over the next few projects.

Current

Current is a measure of the amount of electric charge that flows through a circuit. Using our water analogy, if voltage is the amount of water pressure in a pipe, current is the amount of water actually flowing through the pipe.

Take a look at these two water pipes:

Each pipe has the same amount of pressure pushing the water through, but notice that the second pipe is smaller than the first. Because the second pipe is smaller, less water will flow through it, despite having the same amount of pressure.

What if we wanted to get the same amount of water through the second pipe as the first, but we couldn’t change the size of the pipes? The obvious solution would be to increase the water pressure in the second pipe:

In an electric circuit, this would be equivalent to having to increase the amount of voltage (charge differential) in the circuit in order to get the same amount of charge to flow.

But, what does it mean to have a “smaller pipe” in a circuit? That’s where “resistance” comes in…

Resistance

If voltage is analogous to the amount of water pressure in a pipe, and current is analogous to the amount of water actually moving through the pipe, then resistance is analogous to the size of the pipe being used. The smaller the pipe, the harder you have to push to get the same amount of water through the pipe. In a circuit, that equates to the higher the resistance of the circuit, the more voltage you need to generate the same amount of current.

But, in a circuit, wires are generally the same size. So, you might be wondering -- what causes different amounts of resistance in an electric circuit?

The answer is that lots of things can impact the resistance of a circuit, including type of conductors being used (the material through which the charge is flowing) and the resistance of the components being used. As an example, different types of wire will have different levels of resistance, which will ultimately impact the current and voltage levels within the circuit. And some mediums – like air – have a nearly infinite resistance, meaning electricity won’t flow through it at all. In addition, there are lots of times where we need to add resistance to a circuit (using things called “resistors”) in order to control the flow of current in the circuit.

Btw, we just said above that charged particles won't flow through air, but that's not completely true.  Lightning is a great example of electricity moving through air, but in order for electricity to move from the clouds to the ground, it requires a tremendously high voltage (meaning a tremendous difference in charge from the clouds to the ground).  In fact, the voltages in a lightning strike are about a hundred million times greater than what we'll be working with in our circuits.

Power, Load, Ground

In all circuits, we can talk about three parts of the circuit:

  1. Power:  This is the point of highest charge in your circuit -- for example, the positive terminal of your battery. This point in a circuit is sometimes generically called "Vcc" or in the case of the projects we'll be doing, "3.3V" (since the power source we'll be using will be 3.3 volts).

  2. Load:  The part of the circuit that uses the charged particles -- the components in the circuit -- is typically referred to as the Load.  Above we talked about circuit resistance -- the Load is the parts of the circuit that provide resistance.  An example from our earlier circuit would be the lightbulb -- that is a part of the circuit Load.

  3. Ground:  In an electric circuit, Ground is the point of lowest charge in the circuit.  For example, in our lightbulb circuit above, the negative terminal of the battery is the point of lowest charge, and would be the physical ground point of this circuit.  Interestingly, the reason we use the term "Ground" is because in many electrical applications (like the electricity running through your house), the earth is used as both our reference point of lowest charge and our physical point of attaching the electrical circuit.  This is because the earth is able to receive nearly infinite amounts of electricity without increasing its total charge, so we can always assume that the voltage between a power source and the earth will be constant.


Grounding Yourself

In our assembly guide, we mentioned that you should "ground" yourself before touching electronic components.  Now that you have a conceptual idea of what ground is, we can explain this further.  Have you ever gotten a static shock by touching someone or something?  I'm sure you have.  Sometimes, electric charge builds up in your body.  This charge is then released -- in the form of a static discharge (or shock) when you touch someone or something that provides a connection to the earth.  Once your body has discharged the excess charge, you don't get anymore shocks -- until, of course, you build up more charge.

If you were to touch an electrical component when you have a charge built up in your body, that resulting static shock that you feel could very well be enough to zap the component and have it stop working properly (we sometimes call this "frying the component.")  So, to avoid frying any electrical components, we recommend that you discharge any excess charge in your body before touching the components.  You can do this easily by touching any piece of metal that is connected via some relatively direct path to the earth.  Since all the electrical outlets in your house are connected to the earth, you can ground yourself easily by touching any piece of metal on any electrical device that is plugged in.  For example, if you have a computer or laptop that's plugged in, you can touch any metal piece on it.  Or, you could touch the screw that holds in a light switch.

All that said, even without grounding yourself, some simple precautions can help lower the risk of frying any components.  First, try to avoid walking on carpet before handling an electrical component (you've probably noticed that you'll get more shocks after walking on carpet).


Resistive Circuits, Open Circuits & Short Circuits 

Where we have electricity flowing from a power source (Vcc), through one or more components (Load) and to a point of lower voltage (many times 0V or Ground), we call that type of circuit a Resistive Circuit.  Creating a resistive circuit is the first step in creating a useful piece of electronics.

Remember our battery and lightbulb circuit above?

This is an example of a resistive circuit.

Sometimes we don't have all the components of a resistive circuit, in which case our electronics will typically not work as expected.  Two common examples are open circuits and short circuits: