(This article is originally published on PACKT Articles, see here.)

In this post, you will see the basic requirements needed for building the RasPi projects. You can't spend even a day without electronics, can you? Electronics is everywhere, from your toothbrush to cars and in aircrafts and spaceships too. This article will help you understand the concepts of electronics that can be very useful while working with the RasPi.

You might have read many electronics-related books, and they might have bored you with concepts when you really wanted to create or build projects. I believe that there must be a reason for explanations being given about electronics and its applications.

Let's cover some of the fundamentals of electronics.

Basic terminologies of electronics

There are numerous terminologies used in the world of electronics. From the hardware to the software, there are millions of concepts that are used to create astonishing products and projects. You already know that the RasPi is a single-board computer that contains plentiful electronic components built in, which makes us very comfortable to control and interface the different electronic devices connected through its GPIO port. In general, when we talk about electronics, it is just the hardware or a circuit made up of several Integrated Circuits (ICs) with different resistors, capacitors, inductors, and many more components. But that is not always the case; when we build our hardware with programmable ICs, we also need to take care of internal programming (the software). For example, in a microcontroller or microprocessor, or even in the RasPi's case, we can feed the program (technically, permanently burn/dump the programs) into the ICs so that when the IC is powered up, it follows the steps written in the program and behaves the way we want. This is how robots, your washing machines, and other home appliances work. All of these appliances have different design complexities, which depends on their application. There are some functions, which can be performed by both software and hardware. The designer has to analyze the trade-off by experimenting on both; for example, the decoder function can be written in the software and can also be implemented on the hardware by connecting logical ICs. The developer has to analyze the speed, size (in both the hardware and the software), complexity, and many more parameters to design these kinds of functions. The point of discussing these theories is to get an idea on how complex electronics can be. It is very important for you to know these terminologies because you will need them frequently while building the RasPi projects.

Voltage

Who discovered voltage? Okay, that's not important now, let's understand it first. The basic concept follows the physics behind the flow of water. Water can flow in two ways; one is a waterfall (for example, from a mountain top to the ground) and the second is forceful flow using a water pump. The concept behind understanding voltage is similar. Voltage is the potential difference between two points, which means that a voltage difference allows the flow of charges (electrons) from the higher potential to the lower potential. To understand the preceding example, consider lightning, which can be compared to a waterfall, and batteries, which can be compared to a water pump. When batteries are connected to a circuit, chemical reactions within them pump the flow of charges from the positive terminal to the negative terminal. Voltage is always mentioned in volts (V). The AA battery cell usually supplies 3V. By the way, the term voltage was named after the great scientist Alessandro Volta, who invented the voltaic cell, which was then known as a battery cell.

Current

Current is the flow of charges (electrons). Whenever a voltage difference is created, it causes current to flow in a fixed direction from the positive (higher) terminal to the negative (lower) terminal (known as conventional current). Current is measured in amperes (A). The electron current flows from the negative terminal of the battery to the positive terminal. To prevent confusion, we will follow the conventional current, which is from the positive terminal to the negative terminal of the battery or the source.

Resistor

The meaning of the word "resist" in the Oxford dictionary is "to try to stop or to prevent." As the definition says, a resistor simply prevents the flow of current. When current flows through a resistor, there is a voltage drop in it. This drop directly depends on the amount of current flowing through resistor and value of the resistance. There is a formula used to calculate the amount of voltage drop across the resistor (or in the circuit), which is also called as the Ohm's law (V = I * R). Resistance is measured in ohms (Ω). Let's see how resistance is calculated with this example: if the resistance is 10Ω and the current flowing from the resistor is 1A, then the voltage drop across the resistor is 10V. Here is another example: when we connect LEDs on a 5V supply, we connect a 330Ω resistor in series with the LEDs to prevent blow-off of the LEDs due to excessive current. The resistor drops some voltage in it and safeguards the LEDs. We will extensively use resistors to develop our projects.

Capacitor

A resistor dissipates energy in the form of heat. In contrast to that, a capacitor stores energy between its two conductive plates. Often, capacitors are used to filter voltage supplied in filter circuits and to generate clear voice in amplifier circuits. Explaining the concept of capacitance will be too hefty for this article, so let me come to the main point: when we have batteries to store energy, why do we need to use capacitors in our circuits? There are several benefits of using a capacitor in a circuit. Many books will tell you that it acts as a filter or a surge suppressor, and they will use terms such as power smoothing, decoupling, DC blocking, and so on. In our applications, when we use capacitors with sensors, they hold the voltage level for some time so that the microprocessor has enough time to read that voltage value. The sensor's data varies a lot. It needs to be stable as long as a microprocessor is reading that value to avoid erroneous calculations. The holding time of a capacitor depends on an RC time constant, which will be explained when we will actually use it.

Open circuit and short circuit

Now, there is an interesting point to note: when there is voltage available on the terminal but no components are connected across the terminals, there is no current flow, which is often called an open circuit. In contrast, when two terminals are connected, with or without a component, and charge is allowed to flow, it's called a short circuit, connected circuit, or closed circuit.

Here's a warning for you: do not short (directly connect) the two terminals of a power supply such as batteries, adaptors, and chargers. This may cause serious damages, which include fire damage and component failure. If we connect a conducting wire with no resistance, let's see what Ohm's law results in: R = 0Ω then I = V/0, so I = ∞A. In theory, this is called infinite (uncountable), and practically, it means a fire or a blast!

Series and parallel connections

In electrical theory, when the current flowing through a component does not divide into paths, it's a series connection. Also, if the current flowing through each component is the same then those components are said to be in series. If the voltage across all the components is the same, then the connection is said to be in parallel. In a circuit, there can be combination of series and parallel connections. Therefore, a circuit may not be purely a series or a parallel circuit. Let's study the circuits shown in the diagram.

At the first glance, this figure looks complex with many notations, but let's look at each component separately. The figure on the left is a series connection of components. The battery supplies voltage (V) and current (I). The direction of the current flow is shown as clockwise. As explained, in a series connection, the current flowing through every component is the same, but the voltage values across all the components are different. Hence, V = V1 + V2 + V3. For example, if the battery supplies 12V, then the voltage across each resistor is 4V. The current flowing through each resistor is 4 mA (because V = IR and R = R1 + R2 + R3 = 3K).

The figure on the right represents a parallel connection. Here, each of the components gets the same voltage but the current is divided into different paths. The current flowing from the positive terminal of the battery is I, which is divided into I1 and I2. When I1 flows to the next node, it is again divided into two parts and flown through R5 and R6. Therefore, in a parallel circuit, I = I1 + I2. The voltage remains the same across all the resistors. For example, if the battery supplies 12V, the voltage across all the resistors is 12V but the current through all the resistors will be different. In the parallel connection example, the current flown through each circuit can be calculated by applying the equations of current division. Give it a try to calculate!

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