Okay. So we just talked about hardware a lot. We've talked about all the different metrics that you'd use to measure electricity flow, all the different components, how they plugged together and things like that. Next, what we're going to do is we're going to get into some of the details. We're going to talk about specific components and how they work. To make this more applicable so that we can understand how these things are applied, I want to talk about this in the context of a set of use cases. So we're going to talk about a set of real-world use cases that are common that come up when you build IoT devices, and then I'm going to talk about a set of components that you can use to solve each of these use cases to give us some intuition on how these products and systems are designed. So for example, suppose you want to build something that lights up. You want to build something that indicates its status, some smart sweater that indicates the users temperature or some device with a display that indicates some information about the device. Something that lights up or indicates information. How can we do that? Well, it turns out that there are components that can produce light. One very common component, which you see all over the place is a light emitting diode. Here we have a green one that I'm showing here. There's also various displays which have little tiny points of light that we can control in different ways to display images. We can also actually use light to transmit information. We can encode audio or video in patterns of light and use that to transmit light over a cable. So there is these different components that use light to convey information or create illumination. So when we think about these different components, when we choose between them, they're different, and so there are certain metrics that are important here. So we can talk about brightness. How much light is created by one of these components? We can talk about viewing angle. Do you have to view the display head on? What if you're 30 degrees off? Is it just as bright? There's also color, the different colors of light. There's also things like voltage in current, how much electricity can these things handle without shorting out? So there are these different metrics, and then there's different units for each of these metrics. So brightness, you measure in Candela or knits, viewing angles in terms of degrees, different ways to measure color, and voltage, and current, and so on. So when you choose our components, you can think about what metrics are important to you, and think about what values for these metrics that you care about, and then you can choose components that have those values. So for example, if we talk about color. One interesting question is how you measure color. There's two common ways to measure color. One way is in terms of wavelength. So it turns out that light has a lot of properties of waves. You can think of light as being a wave, and color is actually the frequency of that wave. So if you have some light, light oscillates with a pattern and as you increase the oscillation speed, it gets more blue, and if you decrease, it gets more red. So what we can do is we can talk about the wavelength of light. So it turns out that if you have light and it's around 500 nanometers for the wavelength, then that's a green color. It was around 400, that's more of a purple color, and so on. So what manufacturers do if they want to talk about color, they can talk about the nanometer wavelength of light produced by that device. Another way that we can describe color is in terms of black body radiation. So it turns out that if you have an object, any object, all objects radiate light based on their temperature. Even if just have like a piece of steel or something, it is actually radiating light. Oftentimes, you can't see that light because it's infrared, it is outside the visible spectrum. But as you heat up elements, they go through this progression of color whereas it get hotter and hotter, they produce more and more intense grades of light. So I wonder if you've ever had a barbecue, or you have a electrical stove, or you have a burner, and you heat that up, when it starts getting high, it might be black or red. But as it gets hotter and hotter, it gets more and more orange, and then maybe it might start getting yellow and so on. So the lower diagram here is the color spectrum of black body radiation. If you take something and you heat it up, it'll get more yellow and then it'll get white, and it'll get a blue, and then it'll get outside the visible spectrum. So another way to measure color is in terms of temperature, black body temperature. So if we talk about white like a daylight white maybe 4700 Kelvin, something more yellow might be 3200 Kelvin, and so on. So if you go to the hardware store and you choose out light bulbs or something like that. Light bulbs are often measured using black body radiation for temperature. So this is the way that color is often measured. So I described some components that produce light. There's actually a lot of different components that produce light. To give you an overview of the space. There's different LEDs. They differ in terms of size and what color they produce and things like that. There's LEDs that produce infrared light, there's LEDs that produce ultraviolet light, and a lot of these technologies are based on diodes. There's also photo-transistors, which can also produce light as well. There's also components where they'll take a set of LEDs and arrange them in useful patterns. You may have seen seven-segment displays, where they'll take LEDs and arrange them in an eight diagram, and you can light up certain ones and display certain numbers and letters, or there might be arranged like bar graphs, and so on. There's also light matrices, where you can take sets of LEDs and arrange them in certain patterns to display images. There are shift LEDs, where you can make them flush mounted to different objects. Their sequence. So if you want to have something that's very light, they can put on clothing. You can use that. There's also back light modules. If you want to display something in front of a LED, you can use those. There's electro-luminescence wires. If you need something really long that you can light up, you can use those. There's light pipes and LED strips. There's also different technologies to produce light. There's incandescent bulbs, those are an older technology. There's lasers. There's also LCD displays, where you can display text and so on. There's also ways to use light to signal information. So at the top here, I have a photo interrupter, and that's useful if you have something like a door, you want to see if your door is closing. What would a photointerrupto does is, it's got a little light creator and a light sensor in it and it can sense if something comes between them. So if you have something that comes in and blocks the light, you can detect it using a photointerrupto. So that's useful for detecting movement, and speed, and things like that. There's also optocouplers. Optocouplers are devices where, if you have a circuit and you have another circuit and you need to talk to each other, but you don't want to have them electrically coupled. Maybe one is really high voltage, or one's touching water, or something like that, you can use an optocoupler and it'll couple the circuits together using light. So you can transmit information between them, but no electricity flows between them. There's also devices that convert different light intensities to different frequencies or encode data using optical as well. So when you build something, you can think about what you want to build, what light you want to display, and you can use this slide as a cheat sheet for starting to think about all the different components out there and figuring out what you want to use in your designs.
