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A Basic Tutorial for 1st Year Students:

The Very Basics of Practical Electrical Circuit Building

For an Electrical Engineer, the atoms of any electric circuit are Resistors, Capacitors and Inductors. Resistors are nothing but intentional or non-intentional blockades to the path of current flow. Resistors are available in the market in standard wattage and resistance values. Capacitors and Inductors are distinctly different from resistors in the sense that, they can capture and store the energy provided to them by the power supply instead of dissipating it into heat, as in case of a resistor. Capacitors and Inductors again have a fundamental difference, Capacitors store energy with Electric Fields while inductors do the same with Magnetic Fields.

Assuming that you are acquainted with preliminary electrical networks, Ohms law and Kirchhoff’s Current and Voltage Laws, say, you want to “test” KCL in your small laboratory you have made in your room.

What would you need??

You definitely need resistors of required resistances.
You will need a power source to give life to your circuit.
You will need some place to arrange your circuit components neatly for better understanding of your circuit and proper handling (to make sure no loose contacts remain).
Connecting Wires and wire strippers to put things together.
You need measuring instruments to measure the current and voltages.

Let’s go step by step!

Need A)

Well! You go to a shop and ask for a resistor!

The shopkeeper asks you, what is your desired value of resistance?

If you ask for a 432.95 Kilo-Ohm Resistor, the shopkeeper won’t be able to give that to you!

Resistors are available only in quantized standard values. To make a resistor of your desired resistance you have to make use of parallel and series connections to make the value of resistance you want!

Now, if you ask for a standard value, the resistor you get looks something like this:

Does this convey any information to you? What is the guarantee that you have been given the correct value of resistance?

Well, the colour bands on the resistances have some meaning and are not for decorative purposes! These bands can give you the informations about the approximate resistance value and percentage tolerance of this resistor.

Refer to the following links for details on Resistor Colour Coding:

Need B)

Now that you have the “passive” element, the resistance, with you, you need the “active” one, the power source, to drive your circuit.

The simplest DC power source is a battery!

You go to the shop again, and ask for a battery. Commonly available battery voltage ratings are 1.5 volts,9 volts etc.

A 9 Volts Battery A 1.5 Volts Battery

Now, another problem! What if you need a 3 Volt battery?

Well, you either make a series connection of two 1.5 Volt batteries, or make a “potential divider” arrangement with a 9 V battery (divide 9 by 3, you get 3!!). The first solution would be easier. The circuit diagram for the second solution is as shown below.

Here 3 identical resistors are used to divide the 9 volt into 3 3 volt sections. However practically you will never get a 3 V as shown, even if the battery is an exact 9 V source and the three resistors used are exactly equal. (Think about it!!!).

Need C)

You can’t keep your resitors and battery sources just hanging in mid air! You need to place them somewhere neatly, so that you can make a schematic of the circuit in pen and paper and then implement that schematic in an organized manner.

Also, to attach a resistor to a battery, you can't just twist resistor terminals together and stuff the end connections into battery terminals. With high probability, your circuit will fail, because of loose contacts and also will be unreliable, the unreliability being an increasing function with respect to the size of your circuit!

So, what do you do?

As beginners , you use a breadboard!

It consists of a matrix of slots as shown; you can plug in your resistors, and power devices into the slots any way you like!

Well, not actually any way! The breadboards have a particular construction and you must abide by the rules instructed to you by that method of construction!
The slots are internally connected as shown below:

Well, yes it does look a little complicated! Don’t worry, you will get used to it soon!!

Here are a few links to help you out with breadboards:

Need D)

You will need wires with only one strand to make connections efficiently on breadboards. Multiple stranded wires will cause loose connections.

Single strand hook up wires are available in the market for these purposes. Wire strippers help you cut these wires into pieces of your desired size and also to remove the insulation at the ends.

Need E)

Suppose that you have already made a small circuit to test KCL as shown below.

10 K and 2.2 K ohm resistors are common standard values available in the market. You already have the 9 Volts battery and now you are ready to make this circuit on a breadboard and test it.

But, how do we actually measure the currents in the various branches and verify KCL?

For that we need a current measuring device or an Ammeter.

For our purposes we usually use a multifunctional device called a “multimeter” which can be used to measure a variety of quantities ranging from Voltage, Current, Resistance, Capacitance etc.

An Analog Multimeter>>

<<A Digital Multimeter