Today we will look at the last component in our 3 part series on basic electronic components, the diode.

Diodes only allows electricity to flow through them in a single direction, this is achieved by the diode having a low resistance, ideally zero, in one direction and a high resistance, ideally infinite, in the other direction. This does mean that diodes are polarized (they have 2 terminal, an anode and a cathode) and the direction in which they are placed in a circuit is of great importance.

Diodes are extremely important in converting AC to DC though their use in a bridge-rectifier, but that is a topic for another post.

Diodes usually have 2 markings on them, a band to indicate the side of the cathode and secondly the diode type code (for example 1N4148) this can be used to look up the maximum voltage and current the diode allows.

Here is the schematic symbol used to represent a diode:




Today we will cover the next in our series of the basic electronic component, the capacitor.


A capacitor is used to store and release electrical charge in a circuit. When the voltage in the circuit is higher than what is stored in the capacitor, the capacitor will allow current to flow in and the capacitor will be given a charge. When the voltage in the circuit drops lower than what is stored in the capacitor it will dis-charge, releasing its stored charge into the circuit. This will cause the voltage in the circuit to temporarily raise.

This is extremely useful as some components, such as electric motors, use more power when they are first activated then when they are already active which can cause a voltage drop in the circuit that can have negative effects on other components in the circuit.

Capacitors help level out these fluctuations in voltage.

There are 2 main types of capacitors, Polarized and Non-Polarized. I will not go into a great deal of detail regarding the differences, but in a nut shell non-polarized capacitors have no implicit polarity and can thus be connected to the circuit either way, whereas polarized capacitors have a defined + and – terminal and must be connected to the circuit corresponding to its terminal polarity. This also means that non-polarized capacitors are suited for use with AC, but polarized capacitors are strictly only suited for DC as they experience large leakage if the voltage is inverted across its terminals as is the case with AC, which can cause the capacitor to overheat.

The capacitance of a capacitor is measured in Farad(F). For most circuits you will likely work on microFarad(µF) and picoFarad(pF) sized capacitors will be utilised.

Here are the schematics used to represent both polarized and non-polarized capacitors:

Polarized Capacitor

polarized cap            Non-Polarized Capacitornon polarized cap



In a previous post we had a look at transistors, in the next few posts we will look at 3 other basic electronic components; resistors, capacitors and diodes.

Let us start with the most basic of the 3 today, the resistor. As their name suggest, they resist the flow of electrical current through a circuit. The change in current can be determined using Ohm’s Law, which states that the current flowing through a conductor equals the Voltage across the conductor divided by the resistance present in the conductor, or  I = V/R, where I represents current (measured in Amps), V represents Voltage (measured in Volts) and R represents the resistance (measured in Ohms Ω).

Resistors have coloured stripes along their sides which are used to indicate their values, here is the table used for value lookup:

Colour Value
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Grey 8
White 9

A simple way to remember the sequence of the colours is with the rhyme:
Better Be Right Or Your Great Big Venture Goes Wrong.

The last stripe indicates the tolerance of the resistor:

Colour Value
Brown ±1%
Red ±2%
Gold ±5%
Silver ±10%

Here is an example of how to utilise the table:

resistor 220

The resistor above has 3 colour stripes and a tolerance stripe.

Red Red Brown with a Gold tolerance stripe.

This translates to:

2 2 x 10¹ ± 5% = 220Ω ±5%

Now for an example with a Resistor with 5 stripes:

resistor 10k

The resistor above has 4 colour stripes and a tolerance stripe.

Brown Black Black Red and a Gold tolerance stripe.

This Translates to:

1 0 0 x 10²± 5% = 10,000Ω ±5% = 10kΩ ±5%

Here is the schematic used to represent Resistors in a circuit diagram:

Resistor Symbol