Ohm's Law

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From the course by University of California San Diego

Internet of Things: Sensing and Actuation From Devices

88 ratings

University of California San Diego

Internet of Things: Sensing and Actuation From Devices

88 ratings

Have you wondered how information from physical devices in the real world gets communicated to Smartphone processors? Do you want to make informed design decisions about sampling frequencies and bit-width requirements for various kinds of sensors? Do you want to gain expertise to affect the real world with actuators such as stepper motors, LEDs and generate notifications? In this course, you will learn to interface common sensors and actuators to the DragonBoard™ 410c hardware. You will then develop software to acquire sensory data, process the data and actuate stepper motors, LEDs, etc. for use in mobile-enabled products. Along the way, you’ll learn to apply both analog-to-digital and digital-to-analog conversion concepts. Learning Goals: After completing this course, you will be able to: 1. Estimate sampling frequency and bit-width required for different sensors. 2. Program GPIOs (general purpose input/output pins) to enable communication between the DragonBoard 410c and common sensors. 3. Write data acquisition code for sensors such as passive and active infrared (IR) sensors, microphones, cameras, GPS, accelerometers, ultrasonic sensors, etc. 4. Write applications that process sensor data and take specific actions, such as stepper motors, LED matrices for digital signage and gaming, etc.

From the lesson

Terminology/Cheat Sheet (Beginner)

In this course, you will see a lot of new words and acronyms you might not be familiar with. If you feel comfortable with your knowledge of tech terminology, feel free to skip these lessons since they will not affect the overall integrity of the course. If you see something that you want to know a little more about, feel free to watch the video to gain insight on some basic concepts. We do expect you to know the majority of this material before going into the next module, we would recommend going through the lessons as a quick brush up.

Introduction to Lesson 22:01

Electromagnetic Spectrum2:05

Operational Amplifiers3:27

A look back at Lesson 21:03

Meet the Instructors

Ganz Chockalingam
Principal Engineer
Qualcomm Institute of Calit2, UC, San Diego
Harinath Garudadri
Associate Research Scientist
Qualcomm Institute of Calit2, UC, San Diego

Ohm's Law.

Enough said.

[LAUGH] It is a very important concept

that I think everyone that deals in electronics should know, actually.

There are three, actually four, I guess you could say,

main components of Ohm's Law.

You have voltage, Current, resistance, and power.

>> Resistance and power.

>> So let's take a look at some diagrams that might help us to remember what

Ohm's Law is kind of all about.

>> Okay so Ohm's Law is basically just, V=IR,

which is voltage is equal to the current times the resistance.

It will be helpful if you have any circuit pumps to solve.

This diagram's very helpful, because as you can see,

V on top is equal to the I times R on the bottom.

Or if you simply want to figure out,

just say the current, it's going to be the I equals the V over the R.

And finally, resistance is voltage over current.

>> Yeah, this is a really cool concept.

Because if you're ever dealing with a circuit, and

we're going to go over an example in a little bit.

But, for instance,

you have a component that will burn out if you put too much voltage into it.

>> Right. >> Or too much current.

So you have to determine how much resistance you need in order

to match the specifications of that particular component.

Now, for instance, if you have a component that can only take three volts,

you want to make sure, and you have a five volt input.

Well, you need to make sure that you provide, or that you give the resistance

needed in order to To bring that voltage down, right?

>> Yeah, to make sure you don't burn out your component or your electronic device.

>> Now granted, you're gonna need the current.

So there are gonna be given values or whatever in your problems.

But in real life, you have a multimeter.

You can pull certain values from stuff and work out your circuit.

This is a great tool to use.

Now something up on the screen there that you can see is this little wheel here.

This is a great tool I use that I use throughout a lot of my circuits classes

when we had to analyze circuits, Ohm' s Law.

There were the three equations that he kinda showed.

V equals IR, I equals V over R And then r equals v over I.

But they can have different variations and

if you use this wheel you can see that you have the i, e which is volts.

R resistance and p is power, so all these different variations should work for

you given the parameters that you have.

So if you only have the power and the resistance,

then you can take the square root of it's ratio And get your current.

If you have the power and the voltage

then you can take it's ratio of the voltage squared and get it's resistance.

So that's like the middle on on the R side of the wheel.

Very good one, pause this, Copy this down, search online.

This is a great tool.

I'm surprised that a lot of people don't know about this wheel.

>> Yeah. >> But, great tool get it going.

Time for an example?

>> Yeah, let's go check out an example.

We have a little diagram here we have a power source, spikes voltage.

We have a lamp that has its own internal resistance.

And we're trying to figure out what is the current flow through the circuit.

>> Yeah, so it's a completed circuit.

On the left side, you have the power source, right?

So you have a 12 volt battery, for instance.

You can just call it that.

You can see the plus size is on the bottom of the battery.

Negative side is on the top of the battery, or

on the top of the diagram, I should say.

So yeah, conventionally we measure the current going in the direction of the plus

sign and we want to know what that current is given the voltage and the resistance.

So how would we do that?

What's Ohm's law?

>> Let's see, Ohm's law says that V=IR, but we want to solve for R.

Current.

So I equals V over R.

>> All right, do we have that?

>> V = IR.

We're gonna solve for I.

We have the I =V/R.

What are the two values we have?

Well, V = >> 12.

>> And then- >> R is 3.

So we have 12 volts over 3 ohms, and that equals four amps.

>> Okay. So now if we had a device there that

couldn't handle four amps, what would we do to get less current?

>> So we would have add a resistor, say, to the circuit or

increase the resistance somehow.

>> Perfect.

So yeah.

If we had a device that couldn't handle four amps and

it could only handle three amps,

if we increased that resistance to four ohms Well then, we would get i equals 3.

>> Nice.

>> Perfect.

So we have officially created a circuit on paper.

And then before we burn out our device we calculated what we needed and

we implemented it.

>> So no money wasted, no materials wasted.

Ready to go.

>> Yeah, I would suggest that everyone take some time.

We will provide some supplemental reading materials at the end of this,

to kind of, maybe give you some, actually I think that will be a great idea.

We should give you some little problems that maybe you can do.

Just some simple circuits like this, have some fun with.

And practice,

because core concepts create a good foundation and Ohm's Law is one of those.

Take the time and see us in the next video when you're ready with this.

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