Electronics 101 - Part 1

Electronics 101 - Part 1

In this series of guides I'll be introducing you to the concepts and practicalities of electronics, and how to use this essential and rewarding skill to add a little something special to your PC. Each part will introduce a few concepts and then a practical project or skill that demonstrates these.

In this edition I'm going to take you through the three most basic and important electronics concepts (Voltage, Current and Resistance) and the relationships between them. In the practical section I'm going to show you how to check and measure Voltage, Current and Resistance with a multimeter.


I remember in my childhood the amazement I felt watching my Amstrad Personal Computer start up for the first time, how this strange rectangular block of plastic, its innards littered with silicon and metal strips, could possibly be able to calculate things, store data, even play games! The fascination is still with me and, as I've watched technology develop at such a staggering pace, it is stronger than ever. So what is this mysterious invisible force that flows through a computer that lets you read this guide?: Electricity.

Although we really do take it for granted, electricity is an amazing thing but its also something that can be a difficult concept for people to grasp. It needn't be.

To understand electronics you need to know about three fundamental concepts: Voltage, Current and Resistance. Although there are literally hundreds of (often flawed) analogies out there I think by far the best way of explaining it is to actually look at what electricity is.

Electricity is an atomic phenomenon, it occurs when electrons move through an electrically conductive material. Electrons are one of three particles that make up atoms and are small packets of charge, this idea we shall call our Atomic Model. Electricity has three properties which we have already mentioned:

Voltage: This is much more appropriately called potential difference. In our atomic model it is the force that pushes or pulls the electrons through the wire. Voltage can either be positive (+), neutral or negative (-) and is measured in, you guessed it, Volts. To calculate voltage simply subtract the highest voltage in the circuit (or the most positive) from the smallest (or most negative). Some common examples: 9V-0V=9V, 12V-5V=7V, 12V-(-12V)=24V, etc.

Current: In our atomic model this is simply the flow of electrons through a conductor. It is measured is Amperes or Amps and expressed (in equations) not as 'C' like you would expect but as 'I'. Current is what give electricity its kick, I've had 20,000V passed through my body, it tickled; this is because it had virtually no current behind it.

Resistance: This is simply any resistance posed to the movement of the electrons in a circuit, this will reduce the voltage and limit the current. It is represented as 'R' and is measured in Ohms. Everything has a resistance, resistors (of course) are easy ways to lower the voltage/current. Remember, even wire has a resistance but we tend to ignore this because it is so small.


A diagram helping to explain the Atomic Model and Resistance. The black dots are atoms, blue are free electrons, the thinner middle section provides resistance which reduces the movement of electrons. Its important to remember that the movement of electrons before this resistance will also be slowed.

Now that we know about what Voltage, Current and Resistance is, we need to know how they are related to each other. This is explained with a really easy formula called Ohm's Law which states that Voltage = Current x Resistance (V=IR).


Ohm's Law is often remembered as a triangle. Simply cover up the letter representing what you want to find and use the equation it shows.

Ohm's Law is used a lot in electronics so lets do some examples...

1) A component is using 0.1amps of current and has a resistance of 120 Ohms, what is the voltage across it?: V=IR so V=0.1*120 =12volts

2) A component has 24volts running through it and has a resistance of 10Ohms, how much current is it drawing?: I=V/R so I=24/10 =2.4amps

3) A component has 12volts across it and is using 3amps of current, what is its resistance?: R=V/I so R=12/3 =4ohms

Now lets move on to some practical work...

Practical Knowledge

A multimeter is a truly essential tool for any hobbyist or professional electrician. They range in price and specification, but I have short listed a few recommendations for you here:

212 Digital Multimeter - Rapid Electronics ( 85-0662, £7.50)
Mini Digital Multimeter - Maplin (UZ86T, £8.50)
Auto Ranging Pocket-Sized Digital Multimeter - Maplin (N49AB, £12.76)
955 Autoranging LCD Multimeter - Rapid Electronics (85-0732, £29.50)

Once you've got yourself a nice multimeter you need to know how to use and get the most out of it. Multimeters are so feature packed that they can often be quite bewildering to the first-time user. We'll be looking at four of its capabilities, but before we can start we need to know about something called 'ranging'.

The multimeter is a very simple device to operate, simply select what you want to measure on the dial and touch the probes to what you want to measure. try to make sure that you always touch the positive (red) probe to the most positive side of what your testing and the negative (black) probe to the most negative side, for some things this doesn't apply like continuity or resistor testing (discussed later).


Here's what my meter looks like, its the "955 Autoranging LCD Multimeter" from Rapid Electronics.

If you've not invested in an 'autoranging' multimeter knowing about ranging is essential. You select the range by turning the dial in the centre of the meter to the next highest number you want to measure, for instance if I was to measure the voltage of a 9v battery I would select '20 V' on the dial of my meter which would probably give me a reading of about 8.683 or something similar, if I was to measure a 24v battery I would have to select '200 ' on the dial, get it? For measuring things other than voltage it becomes a little more complex, taking resistance as an example, to measure a 130 Ohm resistor I would set my dial to 200Ohms and get a reading of 122.4 or similar, however; if I was measuring a 220 Ohm resistor I would have to set the range to 2K Ohms, this would give me a reading of 0.214 or similar which translates to 0.214Killo-Ohms or 0.214*1000=214Ohms. If you're unsure of the value you are measuring always start at the highest range and work your way down until you get a good reading. For more specific information on the operation of your multimeter consult your manual.

Now we know all about ranging we can look at how to get correct measurements from a circuit/component without blowing your meter. We're be looking at 4 main measurements, Voltage, Current, Resistance and something called the 'Continuity Test':

Measuring voltage: To measure voltage simply select V on your meters dial and set the appropriate range then just touch the probes around the component that you wish to know the voltage across.


Measuring current: To measure current select A and the appropriate range on your meter then insert the meter before (or after) the component you want to measure in the circuit, so the current first flows through the meter and then the device.


Measuring resistance: To measure resistance simply select Ohms and the appropriate range on the meter and then connect the device around what you want to test. Always disconnect any power from what your testing to avoid damaging your meter.


Continuity checking: Continuity checking is basically checking for a good electrical connection between the probes, if one is found the meter will bleep. Its very useful for checking wires and circuit boards for breaks. To check for continuity select continuity (usually a sound-wave/buzzer symbol) and simply touch the probes on the wire or component you want to test for a clear electrical connection. Always disconnect any power from what your testing to avoid damaging your meter. Try to keep the probes as still as possible as it may take a moment for the meter to react, if there is a good connection you will hear a beep, if not, there will be no noise at all.


Phew! I think that's enough for this part of our guide. I hope you've enjoyed reading this and have learnt something along the way. Part 2 of 'Electronics 101' will be focusing on circuits; the two ways of wiring them (series and parallel) and how to prototype them quickly and easily.

Until next time, happy soldering!

Matt Jason H
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