Lesson video

Hello.

My name's Mrs. Taylor and I'm really glad you can join me today.

Today our lesson is Electronic systems, and this is part of the unit Core principles.

Let's begin.

The outcome: I can use electronic components to design and test electronic circuits.

We have several keywords.

Ohm's law, which is the relationship between voltage, current, and resistance.

Breadboard, which is a device used to plug in electrical components and test circuits.

Polarity.

This is the directional flow of electrons from one pole to another.

And resistance, the opposition to the flow of current.

In this lesson, we have three learning cycles: Designing electronic systems, Modeling electronic systems, and Manufacturing electronic systems.

We begin with Designing electronic systems.

When designing electronic systems, it is important to understand the three concepts shown in this table.

Voltage, which is the electromotive force, measured in volts.

Current, which is the flow of electrons, measured in amperes, sometimes abbreviated to amps.

And resistance, the opposition to the flow of current, and this is measured in ohms.

In 1827, Georg Simon Ohm published a paper which described the relationship between these three concepts.

This is known as Ohm's law.

This table shows the Ohm's law formulas.

To calculate voltage, I need to use current times resistance.

Please note that the I is how we represent current when writing a formula.

So voltage equals I times R.

Current is V over R, so that's voltage divided by resistance.

And resistance is V over I, which is voltage over current.

Let's have a check.

What is the measure of electromotive force?

Pause the video and have a go.

Well done.

Let's check.

That's right, voltage is the measure of electromotive force.

This simple circuit has a cell battery, a resistor, and an LED.

Many components have a maximum rating.

This LED's maximum current rating is 0.

03 amps, and it uses two volts of the five volts in the circuit.

This is known as the voltage drop.

In other words, the LED uses two volts of the available five.

V equals five volts minus two volts, and now we have three volts remaining.

To find the information out about the maximum rating for each component, we look at a data sheet, like this one here for the LED.

Components with a maximum rating can become damaged if these values are exceeded, so it is important to check the data sheet.

To calculate the correct value for the resistor in this circuit, we use this equation: V over I equals three volts over 0.

03 amps.

Remember that the circuit has five volts, but the LED uses two of those and we have the voltage drop, which means that the number we need to use in the calculation is three volts, and so the calculation is three volts divided by 0.

03 amps.

And the answer is 100, and we know that resistance is measured in ohms, so the answer is 100 ohms.

Here we have a check.

Calculate the value required for this resistor.

The voltage drop has been completed for you.

So the voltage drop is nine volts minus two volts, which equals seven.

Pause the video and have a go.

Fabulous.

Let's check.

Again, it's V over I, voltage over current, and we have seven volts over 0.

007 amps, which equals 1000, so the resistor we need here is a 1000 ohm resistor.

1000 ohms is abbreviated to 1 kilo-ohms or 1k ohms.

Electronic systems use a range of components to create circuits with specific functions.

These components can be grouped into input, process, and output components.

This systems approach is useful when designing a circuit.

Input components produce a signal.

They can be categorized as sensors or switches.

Sensors include those which respond to light, sound, or temperature.

Switches can be operated physically or controlled in other ways, such as with a magnet.

Here we have a check.

Match the description to the input component.

A, an electromechanical switch controlled by a magnet; B, a component where the resistance changes due to the temperature; and C, a component where the resistance changes due to light levels.

And here are the three components.

Pause the video and have a go.

Wonderful.

Let's have a check.

C, a component where the resistance changes due to the light levels is an LDR, a light-dependent resistor.

So that was number one.

B, a component where the resistance changes due to the temperature, the answer is two, a thermistor.

And A, an electromechanical switch controlled by a magnet is a reed switch.

Well done.

Process components respond to input signal to control an output.

Process components include transistors and an integrated circuit, which is abbreviated to IC.

Here we can see a picture of a transistor and one of an integrated circuit.

Transistors respond to a small current flowing to the base, which then enables a large current to flow between the collector and the emitter.

We can see here the small current flowing to the base symbolized with a small arrow, and this allows a large current to flow from the collector to the emitter, symbolized with a large arrow.

Output components have visible, audible, or movement outcomes.

For example, an LED is a visible outcome, a buzzer is an audible outcome, and a motor is a movement outcome.

Identify from these images which ones are process components.

Pause the video and have a go.

Let's check.

That's right, it's the IC, the integrated circuit.

Polarity is the directional flow of electrons from one pole to another.

Batteries, LEDs, and capacitors are polarized components.

They have polarity, so must be placed the correct way round in a circuit.

The diagram shows that the current flows from the positive anode to the negative cathode, and we can see that with the arrow.

Non-polarized components allow the electrons to flow either way.

Non-polarized components such as resistors and LDRs can be placed in the circuit either way round.

In this diagram, we can see the arrow indicating the flow of electrons could be in either direction.

Here we have a check.

Which of these components are polarized?

Pause the video.

Let's check.

That's right, it's B and C.

It's an LED, which must be placed in the circuit the correct way round, and a battery.

Components are combined to create circuits with specific functions.

This circuit could be used in a security system.

When light is detected, it is indicated by an LED, which could be changed to an audible alarm.

As the light level increases, the LDR's resistance decreases, allowing a small current to flow to the base of the transistor.

This then allows a larger current to flow between the collector and emitter, switching on the LED.

Your first task.

Label the components in this circuit.

Identify the input, process, and output component from this circuit.

And explain the function of this circuit.

Pause the video and come back to me when you're ready to check.

Okay, let's check.

Well done.

Label the components.

The LDR, the light-dependent resistor, a battery, a resistor, another resistor, an LED, light-emitting diode, transistor, and a third resistor.

Well done.

The input is the LDR, light-dependent resistor, the process is the transistor, and the output is the LED.

And part three.

This circuit uses a light-dependent resistor to sense the light level and a transistor to process the input.

A small current flows to the base of the transistor, which enables a large current to flow between the collector and the emitter.

This then illuminates an LED as the output.

And now we move on to the second learning cycle, Modeling electronic systems.

Electronic component symbols are simplified pictures which are used to communicate circuit designs and create schematic diagrams.

They are easy to replicate and interpret and much quicker to draw than the components themselves.

For example, a battery symbol, an ammeter, LED, resistor, buzzer, and transistor.

Let's have a quick check.

Why are component symbols used when designing circuits?

A, time-consuming to draw; B, easy to interpret; C, easy to replicate; D, difficult to interpret.

Pause the video.

Okay, let's look.

That's right, it's B and C.

They are both easy to interpret and to replicate.

Electronic circuits can be modeled.

Like all designing, modeling or prototyping are ways of testing and iterating design ideas.

CAD models can be used to simulate and virtually test electronic circuits without having to physically build them.

Here is an example of a CAD circuit model.

And now we're going to watch a simulation of this light-dependent circuit on Tinkercad.

Here is the circuit that we designed in the first learning cycle simulated in Tinkercad.

The first thing we do is go to the LDR and adjust the resistance.

As the light levels increase, the resistance decreases, which triggers the LED illuminating.

Let's have another check.

What are the benefits of modeling circuits using CAD?

Is it A, to simulate; B, to physically build; or C, to virtually test?

Pause the video.

Let's look.

That's right, it's A and C.

Well done.

Physical prototyping using crocodile clips to connect components can also be used to create and test electronic circuit designs.

For more complex circuit designs, breadboards can be used.

A breadboard is a polymer board with copper inside.

Components can be plugged in and circuits tested.

Here we can see a CAD breadboard simulation model, again from Tinkercad, and we can also see a real-life breadboard circuit tested.

We're now going to watch the video of the CAD breadboard model simulation.

The first thing we do in Tinkercad is press Start Simulation in the top right, and then we move to the LDR and the toggle.

And just as in the circuit simulation, we can change the light levels falling on the LDR, which in turn change the LED to be illuminated or not.

And here is Task B.

Using Tinkercad, model the circuit from Task A.

The value of the resistors has been added to the diagram for you.

The second part of the task is to test the circuit, and the third part to describe the circuit, answering the questions: did it work as you expected, and if not, why not?

Pause the video and have a go.

Wonderful.

Let's check.

Here is a picture of the model that I created on Tinkercad.

This is my first model of the circuit.

It did not work as planned.

When I simulated the circuit and changed the LDR light levels, the LED did not illuminate.

I realized the LED was in the wrong way round.

LEDs are polarized and only work one way round.

Also, the value of the resistors was incorrect.

When I changed these, it worked.

Well done.

We move on to the third learning cycle, Manufacturing electronic systems.

Electronic systems are manufactured using printed circuit boards, abbreviated to PCBs.

These are made from copper clad reinforced plastic, which is abbreviated to GRP.

Let's have a check.

Which of the following are good electrical conductors?

Is it A, GRP; B, polythene; C, copper; or D, MDF?

Pause the video.

Let's check.

That's right, it's copper.

Copper is a very good electrical conductor, and GRP is a good insulator.

Some of the copper is removed to leave tracks and pads.

The current flows between components which are connected by the tracks, similar to wires.

The pads are where small holes are drilled for the component's legs to go into.

These are then soldered into place.

Let's have a check.

Explain how current flows between components on a PCB.

Pause the video.

Wonderful.

Let's have a look.

Current flows between the pads and components through copper tracks.

Well done.

Soldering is a method of joining two pieces of metal with an alloy.

The alloy is heated and melted, which cools and solidifies to create a permanent join.

When soldering, it is important to assess the potential hazards and minimize the risk.

This is called a risk assessment.

Here is the equipment required to solder.

A soldering iron stand with a damp sponge, some solder, a soldering iron, helping hands can be very useful, a fume extractor, and a pair of goggles.

Let's have a check.

Finish this sentence.

Soldering is, A, a permanent joining method using hot glue; B, a permanent joining method using an alloy; or C, a temporary joining method using tape.

Pause the video.

Let's check.

That's right, it's a permanent joining method using an alloy.

Well done.

In industry, soldering is automated and miniaturized.

Here is a video which shows the process of soldering on a small scale.

The steps are: clean the tip of the soldering iron.

Use the soldering iron to heat the join, both the pad and the component leg, for 10 seconds.

Touch the solder on the heated join for three seconds until it flows.

Remove the soldering iron and allow time for the join to cool.

We're now going to watch the video.

See if you can pick out each of those stages.

Here we hold our circuit with the helping hands, and the first thing we do is take a piece of solder and the soldering iron, and we wipe this soldering iron across the damp sponge to make sure that it's clean.

We then hold the soldering iron against the leg and the pad of the PCB for 10 seconds and touch the solder to that join for three seconds.

A good soldered joint is achieved when the join and the tools are clean, sufficiently heated, and the solder is able to flow.

If the join or tools are unclean or not hot enough, the join may not be perfect.

Here is an example of a good solder joint, and here we have examples of ones that are not so successful, such as too much solder may look like a great big blob.

Not enough solder doesn't go all way around the leg of the component.

The joint being too hot, you would notice that the solder would become discolored and much darker.

And a cold joint, where the solder doesn't flow or connect to the track or the leg of the component and becomes more of a blob.

Task C.

Use annotated diagrams to describe the process of soldering on a small scale and describe the health and safety precautions needed.

Pause the video and have a go.

Let's have a look at some of your answers.

Here is a diagram, a sketch of soldering on a small scale.

And here are the stages.

Gather all the equipment needed and heat the soldering iron.

Clean the tip of the soldering iron by wiping it across a damp sponge.

Hold the soldering iron on the pad and component leg and heat for 10 seconds.

Touch the solder on the heated join for three seconds.

Remove the soldering iron and allow time for the join to cool.

Well done.

And the second part is to describe the health and safety precautions needed.

It is important to wear an apron and goggles in case the solder spits.

A fume extractor is also required to remove any harmful fumes from the environment.

Securing the circuit board using helping hands ensures that your hands do not get close to the hot join.

Well done.

Here is a summary of our learning today.

Ohm's law describes the relationship between voltage, current, and resistance.

Ohm's law is essential when designing circuits to ensure the components are the correct value.

Electronic components can be inputs, processes, or outputs.

Electronic systems can be modeled and tested physically or using CAD and virtual simulation.

Soldering components to PCBs is a manufacturing method to produce electronic systems.

Thank you for joining me today, and really well done!