Lesson video

Hello! My name's Mrs. Taylor and I'm really pleased you can be here to join me for our lesson today.

Our lesson today is "Electronic calculations" and this is part of the "Systems approach to design: Sustainable Futures" unit.

The outcome.

I can use calculations to determine the resistance, voltage, or current at a given point in a control system.

There are five keywords.

Voltage, which is abbreviated to V, and this is the measure of the push from a battery that causes charge to be transferred around a circuit.

Current, which is abbreviated to I, which is the rate of flow of charge in a circuit.

Ohms, which is abbreviated to the omega symbol.

This is the unit of resistance.

Resistance, which is abbreviated to R.

This is the property of a material, such as a metal, that opposes the flow of current.

Ohm's law is the relationship between voltage, current, and resistance in an electrical circuit.

There are two parts to our lesson today.

Ohm's law and data sheets.

And then, Calculating voltage, current, and resistance.

We start with Ohm's law and data sheets.

Let's begin.

In 1827, Georg Simon Ohm published a paper which described the relationship between voltage, current, and resistance.

This is known as Ohm's law.

We can use this relationship to calculate the value of voltage, current, and resistance in electrical circuits.

Voltage is the measure of the push from a battery that causes charge to be transferred around a circuit.

Current is the rate of flow of charge in a circuit, measured in amperes, abbreviated to amps.

Resistance is a property of a material, such as a metal, that opposes the flow of current, measured in Ohms. Here we have a check for understanding.

When measuring resistance, which symbol is used? Is it A, I? B, the omega symbol? Or C, V? Pause the video and have a go.

Fantastic.

Let's check.

That's right.

The answer is B, the omega symbol.

Well done.

The Ohm's law formula to calculate voltage is I times R.

The Ohm's law formula to calculate current is V over R.

And the Ohm's law formula to calculate resistance is V over I.

We now have another check for understanding.

Match the correct equation with the concept it can be used to calculate.

V over R is A.

I times R is B.

And V over I is C.

Which is correct for voltage, current, and resistance? Pause the video and have a go.

Wonderful.

Let's check.

A, V over R is used to calculate current.

B, I times R is used to calculate voltage.

And C, V over I is used to calculate resistance.

Well done.

When calculating component values, we often need to change the prefix.

When calculating resistance, 1,000 Ohms is written as 1k Ohms, or one kiloohms. When calculating current, 0.

001 amps is written as one milliamp, which is a thousandth.

To calculate the current in an electrical circuit when the voltage is nine volts and the resistance 1k Ohms, or 1,000 Ohms, we would use this formula.

V over R equals 9 over 1,000 equals 0.

009.

The current in the circuit would be 0.

009 amps.

We would write this as nine milliamps.

We can model and test this virtually in Tinkercad.

The device which measures the current is a multimeter set to amps, and it can also be used to measure voltage and resistance.

In this example, it reads 8.

9 milliamps.

And that's simulating the calculation from the previous slide, which is using a nine volt battery and a 1k Ohm resistor.

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

Each electrical component has a data sheet.

The information included will vary depending on the component but will always include voltage and current ratings, alongside key dimensions.

When designing circuits and calculating the correct values of components to use, it is essential to use data sheets.

Here is an example of an LED data sheet.

We have some information and then an image with dimensions.

The information tells us the forward voltage in this example is 2.

1 volts.

This is the minimum voltage required for the LED to emit light.

Luminosity intensity is 275 millicandela.

This is the brightness of the LED.

It's measured in millicandela, abbreviated to mCD.

The maximum forward current in this example is 25 milliamps and this is the maximum current that can flow through the LED without damage.

The operating current in this example is 20 milliamps and this is the suggested operating current for the LED for optimal performance.

We have a check for understanding now.

What information is found on data sheets? Is it A, technical specifications? B, dimensions? C, product reviews? Or D, prices? Pause the video and have a go.

Great.

Let's check.

That's right.

It's both A and B.

Technical specifications and dimensions.

Well done.

Here is an example of a piezoelectric buzzer data sheet.

The rated current is 30 milliamps and this is the maximum current that can flow through the buzzer without damage.

Resonant frequencies are between two and three kilohertz.

The frequency a material inside the buzzer will vibrate.

The operating voltage is between 3 and 30 volts and this is the voltage range where the buzzer can operate safely.

And the minimum sound output is 85 decibels in this example and this is the minimum level of sound, which is measured in decibels.

And now we have an example of a DC motor data sheet.

The axle diameter is two millimetres and that's the diameter of the motor's axle.

The typical current.

This is the rated current of the motor, and in this example, it's 350 milliamps.

The operating voltage is between 1.

5 and 4.

5 volts and this is the voltage range for the motor.

And the typical speed in this example is 5,000 RPM.

The typical speed of the motor which is measured in revolutions per minute, RPM.

We now have a check for understanding.

Match the component specification details found on the data sheets to the correct component.

A is minimum sound output 85 decibels.

B is luminosity intensity 275 millicandela.

And C is typical speed 5,000 revolutions per minute.

Pause the video and have a go.

Wonderful.

Let's check.

A is information about the piezoelectric buzzer.

C is information about the DC motor.

And B is information about the LED.

Well done.

We now move to Task A.

Part one.

Define voltage, current, and resistance.

Part two.

State the three Ohm's law formulas used to calculate voltage, current, and resistance.

Part three.

Explain what a data sheet is, and why it is important to source and use data sheets when designing circuits.

Part four.

Source the data sheets for three different components and state the key voltage and current information.

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.

Voltage is the measure of the push from a battery that causes charge to be transferred around a circuit.

Current is the rate of flow of charge in a circuit, measured in amperes, abbreviated to amps.

Resistance is a property of a material that opposes the flow of current, measured in Ohms. For part two, you may have said.

Voltage is I times R.

Current, V over R.

And resistance, V over I.

For part three, your answer may be something similar to this.

A data sheet has all the information about a component.

This information includes the dimensions and technical specifications.

The information included will vary depending on the component but will always include voltage and current ratings, alongside key dimensions.

This is useful when planning a circuit or control system, as then the correct values within the circuit can be calculated using the Ohm's law formula.

And for part four, you may have answers similar to this.

The LED data sheet states the forward voltage is 2.

1 volts and the operating current is 20 milliamps.

The piezoelectric buzzer data sheet states the operating voltage is between 3 volts and 30 volts and the rated current is 13 milliamps.

The DC motor data sheet states the operating voltage is between 1.

5 volts and 4.

5 volts and the typical current is 350 milliamps.

Well done! We now move to the second part of our lesson.

Calculating volts, current, and resistance.

Here is a circuit with a battery, LED, and resistor.

We can use the Ohm's law formula for resistance to calculate the value of the resistor needed to protect the LED.

The voltage of the battery in this circuit is nine volts.

The LED current information can be found by using the data sheet.

Here we have a check for understanding.

What is the Ohm's law formula to calculate resistance? Pause the video and have a go.

Great.

Let's check.

That's right.

It's V over I.

Well done.

The LED data sheet gives us some information.

The operating current is the suggested current for the LED for optimal performance and lifespan.

In this example, it is 20 milliamps or 0.

02 amps.

The maximum forward current must not be exceeded to avoid damaging the LED.

In this case, it is 25 milliamps.

There is no minimum current, but it should operate as close to 20 milliamps as possible to illuminate the LED sufficiently.

The LED data sheet gives the forward voltage.

This is the voltage the LED will need to conduct current and emit light.

This value will need to be subtracted from the total voltage in the circuit.

Resistors are available in standardised values.

For example, standardised resistor values in Ohms range from 33 Ohms all the way to 4K7 Ohms. The smaller number is a lower resistance and the larger number, a higher resistance.

1K means one thousand or 1,000 Ohms. 2K2 means two thousand two hundred or 2,200 Ohms. Here we have a check for understanding.

What is the resistance in Ohms of a 4K7 resistor? Pause the video and have a go.

Great.

Let's check.

Four thousand seven hundred Ohms, or 4,700 Ohms. To calculate the values of the resistor needed in this circuit, calculate the voltage, which is V equals 9 volts minus 2.

1 volts equals 6.

9 volts.

Use the Ohm's law equation, V over I.

So in this example, it would be 6.

9 over 0.

02, which equals 345 Ohms. The resistor needed in this circuit is 345 Ohms. Resistors, however, come in standardised values.

You always round up and not down.

So in this case, we would use a 360 Ohm resistor.

We can also simulate the circuit.

Here is the circuit using a 345 Ohm resistor, which is available on Tinkercad.

Here, a 360 Ohm standard value resistor is used.

This results in a lower current than the calculation but is still one that is acceptable, as it's very close to 20 milliamps.

When designing control systems, multiple data sheets may be needed to identify all the different components and information required to design the system.

Izzy has begun to identify the information she needs to gather for her control system.

The input is to measure the soil moisture.

The process, to check the soil moisture to see if it is too dry.

And the output is, if yes, turn on the water crops indicator LED.

"I will need to know the operating voltage and current for the output LEDs," says Izzy.

We now move to Task B.

Part one.

Calculate the value of the resistor needed in this circuit.

The voltage calculation has been completed for you.

The LED data sheet states the maximum forward current is 25 milliamps and the optimum operating current is 20 milliamps or 0.

02 amps.

Show your working and select the most suitable common available resistor.

Here is the voltage calculation.

4.

5 minus 2.

1 equals 2.

4 volts.

And part two.

Use Tinkercad to model and test this circuit to check the current is suitable.

Pause the video.

Brilliant.

Let's check.

So the calculation for part one is V over I.

2.

4 volts over 0.

02 amps equals 120 Ohms. The nearest commonly available resistor is 150 Ohms. Using 150 Ohms standard resistor has reduced the current to 16.

2 milliamps when compared to the calculation.

This is below the maximum forward current and suitable for the LED to operate.

Well done.

For part three, calculate the current in this circuit and state if the resistor value is suitable.

The maximum forward current for the LED is 25 milliamps and the operating current is 19 milliamps.

The voltage calculation has been completed for you.

Show your working.

So here we have a nine volt battery and a 3k Ohm resistor.

So the voltage calculation, which has been done for you, is 9 volts minus 2.

1 volts.

Part four is to use Tinkercad to model and test this circuit.

Pause the video and have a go.

Wonderful.

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

The calculation is V over R, which is 6.

9 over 3,000 and this equals 0.

0023 amps.

The data sheet states that the maximum forward current for the LED is 25 milliamps and the operating current is 19 milliamps.

Therefore, this is not a suitable resistor, as 0.

0023 or 2.

3 milliamps is not sufficient for the LED to emit enough light.

When using Tinkercad to test and model this circuit, we can see that this is not a suitable resistor, as 0.

0023 or 2.

3 milliamps is not sufficient for the LED to emit enough light.

For part five, calculate the current in this circuit and state if the resistor value is suitable.

The maximum forward current for the LED is 25 milliamps.

Calculate the voltage first.

Show your working.

Here we can see the circuit with a 4.

5 volt battery and a 200 Ohm resistor.

Part six.

Use Tinkercad to model and test this circuit.

Pause the video.

Wonderful.

Let's check.

For part five, the calculation 4.

5 volts minus 2.

1 volts equals 2.

4 volts.

Therefore, to calculate the current, the calculation is V over R, which in this case would be 2.

4 over 200, which equals 0.

012 amps.

The data sheet states that the maximum forward current for the LED is 25 milliamps.

0.

012 amps is the equivalent to 12 milliamps.

This is a suitable resistor for the LED to emit enough light.

And we can see from the model that this works.

We now have a summary of our learning today.

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

We can use Ohm's law formulas to calculate the value of voltage, current, and resistance in electrical circuits.

When calculating component values, we often need to change the prefix.

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

I'm really pleased you could join me for our lesson today.

Thank you, and well done!.