The purpose of this session is to teach you how to use breadboard to construct and test a simple electronic circuit. We will also learn about some common electronic components and some of the terminology used in electronics.
By the end of this session the learner will be able to:
- Read an electronic schematic and recognise the components that go to make up the circuit
- Trace the circuit schematic and built the given circuit on breadboard
- Test the circuit using a power supply
- Produce a report based on the session activities
A drawing of the connections required to make an electronic circuit is called a schematic. The schematic shown below, is the circuit you will be making in this session.
A brief review of what has been covered so far
Lets just start with a very basic description of an electronic circuit. An electronic circuit is made up of a power supply which has a positive connection and a ground connection. Connected between the power supply connections we have a circuit which is made up of various components.
Electrons flow from the power supply, through the components and end up at the ground connection of the power supply. We use the components to produce certain effects such as heat, light, sound and communication.
All electronic circuits have the following common elements:
Voltage (V) produced by the power supply, this is sometimes called potential difference.
Current (I) is a measure of the amount of electrons flowing through the components. Current is measured in amps.
Resistance (R) All components, including the power supply, will to some extent, resist or completely block (diodes and capacitors) the flow of electrons. This is called electrical resistance and it is measured in ohms.
That’s enough to be getting on with. Now lets actually build a circuit that does something
First up we need to know how to use breadboard to build electronic circuits
Now lets quickly look at each of components used to make The Virtual Cat Circuit
The heart of this circuit is the 555 timer. It has many uses but in this circuit we are going to use it as a variable oscillator. Below we have a physical image of the 555 timer and its circuit symbol.
Oscillation means to move ‘back and forth’ between to different states, for example the pendulum on a clock. In electronics a circuit which oscillates is one which switches on and off, therefore we call it an oscillator.
Next up we have the Light Dependent Resistor usually shortened to (LDR). Below we have the image of an LDR and its circuit symbol. Our circuit uses 2 LDR’s
In electronics, all components resist the flow of electrons. The amount of resistance an LDR has depends on how much light is shining on it. With lots of light it has a low resistance, when it gets darker, its resistance goes up.
Then we have an electrolytic capacitor. A capacitor is a component which can both store and discharge an electric charge. Below we have the physical image of the electrolytic capacitor and its circuit symbol. Our circuit uses 2 electrolytic capacitors.
The + sign means that this type of capacitor is polarised (technical term). It just means that its positive + terminal must be connected to positive and its negative – terminal must be connected to ground. There are 2 ways of telling which terminal is negative.
- The shorter leg is negative
- The negative terminal is indicated by a white bar with black dashes along it
This is what happens if you connect it the wrong way around
And finally we need a speaker to produce the sound. A speaker is a transducer, this simply means that it converts one type of energy into another type of energy. In this case a speaker converts electrical energy into sound energy.
The speaker has two connections (terminals). The + terminal should be connected to the negative terminal of the capacitor connected to pin 3 of the 555 timer and the other terminal should be connected to ground.
Reading a Schematic
Of course we could just follow the instructions and build the circuit. However, it is good practice to learn how to read schematics right from the very first lesson. So we will start here.
Testing the circuit. The next video shows you how to connect the power supply and speaker to test the circuit. Have fun.
Having completed the build of your circuit you now need to complete a report. All reports should follow the same basic pattern.
- Main elements of the report (results, descriptions, photographs etc)
Here we have included a very basic example report on this session to get you up and running.
This concludes this session.