Component review


UK Power Networks - Circuit Components

In my previous blog, I detailed how I reviewed my notes in order to ease the process of building my project. This is a continuation with a review of the basic components of a circuit.

Key concept

  • Understand what a resistor, LED, capacitor and transistor do


Resistor Stock Photo - Download Image Now - iStock

Resistor: A resistor is a passive electrical component that implements electrical resistance in a circuit. In audio they are used to adjust signal levels. There are many different types of resistors with different values and they determine how much resistance there is within a circuit.

Different resistors can be identified through the colour of their bands.

Resistor Colour Code
Resistor colour band chart

Transistors: A semiconductor device used to amplify or switch electrical signals and electrical power. In simple terms it can turn a current on or off. The two most common transistors are BJT and MOSFET.
Bipolar Junction Transistor: Has 3 legs and includes 3 parts. Base, collector and emitter. If you turn it on the current will be able to flow from the collector to the emitter. If its turned off then it does not work.

Application of bipolar junction transistor (BJT) - Polytechnic Hub
BJT Transistor

MOSFET: It has 3 pins. Gate, source and drain. One important difference between the two is that in the BJT transistor, the current from base to emitter decides how much current can flow from collector to emitter. In MOSFET transistor, the voltage between gate and source decides how much current can flow from drain to source.

Nettigo: N-channel MOSFET transistor, 60V, 16A
MOSFET Transistor

Why a transistor: A great advantage the transistor provides is that you can use a small voltage/current to control a much larger voltage/current.
Furthermore in audio a transistor allows for the existence of an amplifier on and off state.

Capacitor: Much like the name states, a capacitor stores electrical energy in a circuit. It is a passive electrical component with two terminals allowing for connections to both the positive and negative side. Capacitor work like filters. In audio it is quite literal that they are used in LPF/HPF. A clock is an example of an everyday object that uses a transistor.

How Does A Capacitor Work? - Build Electronic Circuits

LED: An LED or light emitting diode is a semiconductor light source that emits light when current flows through it. Its function is to light up if a current flows through it to show that a current is flowing. It is very common and can be seen in many everyday things such as a laptop.

What Is An LED (Light-Emitting Diode)? - Build Electronic Circuits

Practice makes perfect

Now that the basic components have been reviewed, the best way to understand them is to get a hands on experience with them. For my case, before I begin building my circuit I will build basic circuits with the help of circuit diagrams in order to make the whole project easier to understand.

Circuit Diagram | MyDraw
Circuit Diagram


A Fundamental Review

A rapid review

Ultimate Guide to Audio Output - Headphonesty
Different audio Outputs

Before beginning any hands on work for the melody maker, A rapid fire review of the fundamentals of audio electronics was required for me in order to ensure the project runs smoothly. In this blog I will run through concepts that are key to this project so that it may ease the difficulty of the project. You may also learn something however if you choose to stay and read 😀


First things to focus on were the fundamentals. How do circuits actually work. 2 concepts are key to understanding them:

  • Closed loop
  • Voltage, Current and Resistance

Closed loop: Electrons can only flow if there is a closed loop – a path from the negative to the positive terminal of a battery. An example of where a closed loop occurs is a light bulb. Connecting the light bulb to both the positive and negative side of the battery will allow the electrons to flow in order to make it shine a light.

Voltage: Voltage is what makes the electrons move in a circuit. It pushes them onto a wire and the more we have the more ‘power’ we have. In audio more voltage allows for a louder volume. This is why you tend to see small speakers requiring less volts while big loudspeakers or PA systems would require 50 – 100V. V is the symbol for volts.
Resistance: Resistance is a measure of the opposition to current flow in an electrical circuit. The opposite of voltage you could say. It is measured in ohms. Ω is the symbol for resistance.
Current: Current can be described as the rate at which electrons flow past a certain point in a complete electrical circuit. It is measured in amperes. I is the symbol for resistance.

Ohm’s Law

Ohms Law Tutorial and Power in Electrical Circuits
Ohm’s Law

Ohm’s Law states that electric current is proportional to voltage and inversely proportional to resistance.
To remember Ohm’s law just remember this simple triangle. VIR. Voltage, Current and Resistance. Lets say you want to find voltage for a circuit that you are building. Using the triangle you cover your hand over V and what you are left with is I and R. This means Voltage = Current multiplied by Resistance. Using this formula you can find the voltage if the current and resistance is known. You can also do this with finding the current of a complete circuit. Simply hover your hand over I and we can see that V and R are left. V divided by R = I. Overall this is a simple method to help remember Ohm’s law!

More to learn

Now that we remember how a circuit works, we must know review what components make up a circuit and what their function is. This will be featured in my next blog.