Lesson video

Hello.

My name's Mrs. Taylor.

And I'm so pleased you can be here to join me for our lesson today.

Our lesson today is LEDs.

And this is part of the Systems Approach to Design: Sustainable Futures unit.

The outcome.

I can explain the function of an LED and identify and use them as output components in a control system.

There are four keywords.

Incandescent, which means emitting light due to high temperature.

Watts, which is the measurement of energy consumption.

Light-emitting diode, abbreviated to LED.

And this is an output device that glows when electricity is passed through it.

Electroluminescence.

This means materials emit light when exposed to an electric field or current.

There are two parts to our lesson today, LEDs and LED displays.

Let's begin with LEDs.

The incandescent light bulb was invented in 1879 by Thomas Edison.

He wasn't the first to experiment with electric lighting, but he designed the first commercially viable product.

Here is a picture of an incandescent light bulb.

Incandescent means emitting light as a result of high temperature.

The light bulb is a glass bulb filled with inert gas and a thin wire filament.

When electricity passes through the filament, it heats up, glows, and emits light.

Although revolutionary at the time, one disadvantage of incandescent light bulbs is the high energy use due to the wasted heat.

A light bulbs energy consumption is measured in watts, abbreviated to W.

Incandescent bulbs are from 25 to 100 watts per hour energy consumption, compared to an LED, which are somewhere between two and 18 watts per hour.

Here we have a check for understanding.

Energy consumption is measured in a, volts per hour, b, amps per hour, c, ohms per hour, or d, watts per hour.

Pause the video and have a go.

Wonderful.

Let's check.

That's right, it's watts per hour.

Well done.

An LED is a type of diode.

A diode is a component which allows current to flow in one direction, but opposes, which means does not allow, the current flow in the opposite direction.

Here is an image of a diode.

The anode is the positive connection and the cathode the negative.

And we can see the large arrow showing the direction of current flow.

And here we can see the symbol for a diode, with the anode positive direction of current flow and the cathode negative.

LEDs transform electrical energy directly into light energy.

They are efficient because very little energy is wasted on heat.

Unlike incandescent light bulbs, LEDs are durable.

They are manufactured from solid-state materials that can withstand shock and high temperatures.

Here we can see a picture of an LED zoomed in.

It has an epoxy lens, a semiconductor die, the cathode, the negative connection is the short leg next to the flat surface, and the longer leg, the anode, which is the positive connection.

When the material inside the semiconductor die is exposed to an electric field or current, it emits light.

This is called electroluminescence.

The semiconductor die material is a compound of two different chemicals, such as gallium arsenide or gallium phosphide.

The compounds are different for each colour LED.

Semiconductor die can be seen inside the centre of the LED.

Here we have a check for understanding.

When the material inside the semiconductor die is exposed to an electric field or electric current, it emits light, and this is called a, electroluminescence, b, photoluminescence, or c, hydroluminescence.

Pause the video and have a go.

Wonderful.

Let's check.

That's right, it's electroluminescence.

Well done.

The technical specifications and dimensions of components are detailed on data sheets.

Here is an example for an LED.

We can see the forward voltage is 2.

1 volts.

And this is the voltage which is required.

The luminosity intensity is 275 mCD.

And this is how bright the LED appears in a focused beam at a specific angle.

This is measured in millicandela, abbreviated to mCD.

Max forward current 25 milliamps is the maximum operating current.

Here we have a check for understanding.

What is the maximum operating current for this LED? Pause the video and have a go.

Fantastic.

Let's check.

That's right, it's 20 milliamps.

Well done.

When using an LED with a micro:bit, it is important to use a resistor to limit the flow of current and protect the LED from damage.

In this example, a 1K Ohm resistor is used with each LED.

1K is the abbreviation for 1000 Ohms. We can use the digital write pin code block when using offboard LEDs with the micro:bits.

In this example, offboard LEDs connected to the micro:bit pin 0 and pin 1 would be high, which means turned on when button A is pressed.

We can use if and else code blocks with the light level variable to turn the LEDs on and off.

In this example, the variable is the light level.

If the light level is less than or equal to 20, pin 0 is high, which means on, else, it is low, which means off.

We now move to Task A.

Part one, draw a diagram of an LED.

Add labels to identify the key features.

Part two, explain how an LED changes electrical energy into light energy.

Part three, open the Tinkercad file from the gallery.

Part four, simulate the system and explain what happens when the temperature changes.

Part five, modify the system to include a blue and red LED with resistors.

Part six, modify the programme to illuminate the blue LED if it is below five degrees Celsius, illuminate the red LED if the temperature exceeds 30 degrees Celsius.

And part seven, simulate and explain how this could be used as part of a greenhouse temperature monitoring system.

Pause the video.

Have a go.

Good luck.

Fantastic.

Let's have a look at some of the answers you may have come up with.

For part one, you may have a diagram with the epoxy lens, semiconductor die, cathode, and anode identified.

For part two, you may have said the material in the semiconductor die is electroluminescent.

It emits light when current flows through it.

An LED is a diode where the current flows from the anode to the cathode.

It won't work the other way around.

For part three and four, you may have said, when I move the slider to reduce the temperature, the green LED connected to pin 1 turns off.

I tried it a few times and realised that the green LED emits light when the temperature is between six degrees Celsius and 29 degrees celsius.

For part five, you may have said, I added the blue LED to pin 0 and the red LED to pin 2.

They both also have a current limiting resistor in series.

For part seven, you may have said, I added another if and else block to the programme for the blue LED.

If the temperature is less than or equal to five degrees celsius, the blue LED will emit light.

I added a third if and else block for the red LED.

If the temperature is greater than 30 degrees Celsius, the red LED will emit light.

The three LEDs act like a traffic light system and could be used in the greenhouse to monitor the temperature.

Well done.

We now move to the second part of the lesson, LED displays.

LEDs can be used individually or grouped together in a matrix to display images or words.

The 25 built in LEDs on a micro:bit can be controlled to display text and images.

Here we can see an image of a micro:bit displaying a love heart shape.

Let's have a check for understanding.

An LED matrix is a, a game, b, a puzzle, c, a group of LEDs, or d, an LED.

Pause the video and have a go.

Fantastic.

Let's check.

That's right, an LED matrix is a group of LEDs.

The correct answer is c.

Well done.

The LED matrix on the micro:bit can display a static image or an animated image.

We can see on the left a micro:bit with a static image and a gif showing us the animated image on the right.

Text can be displayed using the show string code block.

A string is a sequence of characters displayed on the LED matrix.

As we can see here, the code says on start, repeat 10 times, show string, Hello.

And on the right, the micro:bit can be seen showing hello scrolling across.

We now have a check for understanding.

Which code block is used to display a sequence of characters on the LED matrix of a micro:bit? Is it a, static image, b, animated image, c, show string, or d, if else.

Pause the video and have a go.

Wonderful.

Let's check.

That's right, the answer is c, show string.

Well done.

We now move to Task B.

There are four parts.

Part one, explain what an LED matrix is and what it can display.

Part two, plan the visual display outputs of your greenhouse control system and explain your choices.

Part three, use Tinkercad to model one of the visual display outputs in your system.

And part four, download this to a physical micro:bit and test it.

Explain the outcome.

Pause the video and have a go.

Wonderful.

Let's have a look at some of the answers you may have come up with.

For part one, you may have said, an LED matrix is a group of LEDs which, when programmed, can display text and images.

These can be static, animated, or even scroll to show words and phrases.

For part two, you may have said, when the light levels are low, I want a light to come on in the greenhouse.

Also, I want different coloured LEDs to illuminate when different temperature levels are reached.

For part three, Izzy says, "I am going to model the automatic light which comes on when the light levels are low." For part four, Izzy says, "I downloaded the programme to the physical micro:bit and tested it.

To test the low light levels, I went under the desk and saw the white LED light up when it was dark." Well done.

We now have a summary of our learning today.

Incandescent means emitting light due to high temperature.

Incandescent light bulbs use more energy than LEDs.

LEDs are more energy efficient due to the movement of particles directly creating light without the high temperatures needed in incandescent light bulbs.

They use special materials which are electroluminescent.

The material compounds can be changed to create different coloured LEDs.

LEDs can be used individually or grouped together in a matrix to display images or words.

They can be controlled by a microcontroller programme.

I'm so pleased you could join me today.

Thank you and well done.