The RJ Journal - Electronics - Basics

2007-05-01

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So what will you need to know before you start with electronic stuff? It is a good idea to have some basic knowledge of the physics behind electricity - to know about volts, amperes, resistance, power and the difference between AC and DC. You don't have to get too involved in the nitty gritty stuff about the subatomic particles, such as electron volt, electric field or electric charges, if you don't want to. We will also cover some of the basics here, just to be on the safe side.

These pages will focus more on the practical side and what is needed to get started. It is my believe that you will learn a lot faster by doing it 'hands on' instead of just reading about it. You will get a much better feel of things by actually doing things physically on the lab bench, both the mistakes and when you get it right.

Naturally, the practical and theoretical sides goes hand in hand - when you see something you don't understand or want to know how to do this or that, you will most likely need to read about it first. But then you need to test, experiment and improvise. It is like this because the practical world in the lab is a lot different from the theoretical world in the books. In the theoretical world all components and circuits are ideal, there are no losses, a resistor is just a resistor, a capacitor is just a capacitor, a circuit board has zero impedance (resistance, capacitance and inductance) in the traces, a pulse has no rise time and so on. This is why it is so important to actually realize the circuits in the real world to get a good feel of things. This is also a good way to get to know the different kinds of components - In the real world they don't look like the schematic symbol from the theoretical world.

A word of caution though - Electricity can be dangerous and even lethal. Luckily, electronic circuits use a voltage that is low enough to be completely safe and the source can mostly be a 9V battery. Do not use any other source than a 9V battery if you don't know exactly what you are doing and do never, under any circumstance, plug your electronic circuits directly into a wall outlet.

What about math, then? To start with electronics you only need to know two formulas:

U = R * I and P = U * I

Where U stands for voltage and is measured in volts, R is resistance and is measured in ohms, I is current and is measured in amperes and P is power measured in watts. We will take a closer look at these formulas in the text about the first component - the Resistor.

To visually imagine how voltage, current and resistance works, electronic and electric circuits can in many ways be compared to water flowing in a closed pipe system. The voltage or the electric potential, the thing that drives the current, a power supply or a battery, can be compared to a pressure produced by a pump in the pipe system. The higher the pressure, the more water can be pushed through the pipes. The water flow itself can be compared to the electric current and the electric resistance can be compared to how thick the pipes are, a high resistance is a thin pipe that makes it harder for the water to flow through it and a low resistance is a thick pipe which lets the water pass easier. To increase the water flow, you can either decrease the resistance by widening the pipes or increase the pressure with a larger pump. This comparison also works if the pipes are divided into several branches - the water flowing in the main pipe is the sum of all the water flowing in the branches connected to the main pipe, with more water flowing in the thicker branches and less in the thinner. This is just a crude model which has many flaws, but it can sometimes help to imagine the invisible current in an electronic system as water in pipes.

When dealing with electronics and electricity, we need to represent a great span of numerical values for various units of measurements. Currents flowing in a conductor could be a very small number, say 1 billionth of an Ampere and a resistor could have a very high resistance, 1 million Ω (ohm), for example. Instead of writing this as 0.000000001A and 1000000Ω we use a prefix before the unit of measurement for the value. This prefix represents a multiplier to the value and is written with a symbol representing the prefix. The values above written with a symbolic prefix would instead be 1nA and 1MΩ, which is much easier to read. The following table shows the prefix (pronunciation), it's symbolic representation and the multiplier for the prefixes that will mostly be used for electronics.

 Note that a numeric value can be written in more ways than one where a different value and a different prefix (multiplier) is used - 0.1MΩ can also be written as 100kΩ, which is the same numerical value. 0.1 * 1000 000 = 100 000 and 100 * 1000 = 100 000.

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