So Internet of things is all about interacting with the physical world. So as we get into this, it's important for you to understand how to interact with physical systems, and we're going to start talking about things like wiring and enclosures in how to deal with the mechanics of IoT. So a Summary View, and we'll talk a little bit about electrical current. So as you'll recall, electrical current is about electrons moving within materials. So if you have a material with electrons in it, you can apply a force to those electrons and it'll cause those electrons to move down the material and we call this current. So when we talk about current flowing through materials, there's different kinds of materials and some materials are more amendable to current flow than others. In particular, if you could take a material and look at it in detail, what you would find is you would find that there's a bunch of atoms, and then there's places where electrons can be. In some materials, if you apply a certain amount of force, you can get electrons in there, and then if you apply more force, you can get those electrons to move, and often these different levels of energy that you apply to these materials can be separated. So if you have a material, there's a certain amount of force you can put in or electron energy you can put into the material that can get electrons in there, and that's called the valence band. That's like a band of energies where can get electrons into the material. There's also another band called the conduction band which is where electrons actually move. So in certain materials like metal, these two bands overlap. There is a region where you can get electrons in there and they can move easily. So in metal, we can move electrons easily and we call these conductors because they're very good at conducting electricity. In other materials like insulators, these bands are separated. So you can get electrons in there. But then there is a huge step you have to do to really push those electrons to get them to move. There's a band gap, and so insulators are not good conductors, and you get electrons in there but it's really hard for them to move. In an in-between there semiconductors where these bands are close. But it's hard to get electrons to cross this gap unless you dope it. So we can talk about conductors and insulators, and when you're building something, when you're building a device, you got to think about where you want electricity to go. You might have wires going around where you went electricity to go in certain directions, you may have physical enclosures where you went to prevent electricity from getting in you want to insulate your device from static or lightening and other effects. So it's helpful to know the properties of different materials and how well they conduct and how well they insulate when you're building devices. So in particular, if you have a material it could be a conductor. A conductor is a material in which your valence electrons wander around easily. It's good at conducting energy. There's also insulators where your valence electrons are tightly bound to your nucleus. So it's hard to move electrons through them, and then they're semiconductors which are in between. So if you're building something where you want to carry electron easily, use a conductor. So materials like copper and aluminum are good conductors. These are used for things like carrying signal and cables, transferring electricity. Insulators are used where you want to separate conductors. So if you want to take a conductor but you don't want to touch another conductor, you can wrap it in an insulator, and for this use things like glass and latex and plastic and rubber, and then there's semiconductors. Semiconductors are what we use to build electronic components like integrated circuits. Semiconductors are things we can easily make them more conductive by adding impurities. So to get a sense of how different these materials are, let me show you some real numbers. So as you can see from this chart, if we have something like glass, glass is an insulator. Glass has a really high resistivity. You can push electrons in it but you're going to need a lot of force to get them in there. Very high resistivity. Same for mica and quartz. Very high resistance to electricity. Something like copper is totally opposite. Very easy to slide electrons through it. So conductors and insulators are different. Now, the next question is if you're building something and you went to conduct electricity, you wouldn't use wires. What specific material should you use? So it turns out there's a lot of different metals. Knowing the properties of these different metals, can help you make more intelligent decisions about your designs. Because you'll know what wires to use in your particular environment. Because they're actually very different. So as one option, we have copper. Copper is used all over the place. Copper is a great material. Is cheap. It has lower strength, and if you've ever taken a piece of copper like a copper wire and tried to bend it, is very easy to bend, has low strength. It's also subject to melting. It has somewhat low operating temperature. Is also subject to corrosion. So if you leave it out and exposed to oxygen, it will turn green, and if you've ever seen the statue of liberty, that thing is made out of copper. But what happened is it it oxidize and it turned green, we are used to that. We probably could scrape all that stuff off. The same thing happens with regular copper wires as well. If they're not coded if they're exposed to oxygen, they will oxidize and that can make problems when you're forming connections between them. Is subject to corrosion from air and also water. It's better at conducting heat than other materials though. So that's why we make pans out of copper sometimes. If you put it on a burner and it will conduct the heat all over the pans. So that's nice. So if you're building a material, you're building a device. It has got a CPU in it. The CPS getting high. You might want to put copper on top of that because it'll conduct the heat away from that which is nice. However, it's worse at radiating the heat. Is good at absorbing heat and spreading it around. It's not good at radiating it because it's a pretty dense material. So copper is really good for wiring. We use it all over the place for wiring. It's also good for flexible parts. If you want to build a wire and the wire is in an environment where it might get bent, might interact with humans or might move around, Copper is a good choice for that. Another very common conductor is called aluminum. Aluminum is less conductive than copper. So if you're building wires, it might be better to use copper wires than aluminum wires. Aluminum also has problems handling load surges. Has some other problems too. Back in the 1970s, there was a shortage of copper, and so for a period of time in the United States, we actually built house wiring out of aluminum, and that worked great for awhile, and then people started noticing there are a lot of fires in these houses. In the problem that happened is that aluminum is not as malleable as copper. If you have two pieces of copper like two copper wires and you twist them together to form a connection, copper squishes together which works really nice for connections. If you have two aluminum wires and you do that, they don't really squish together very well. They're not as squishy and this led to fires because you'd have these little gaps and sparks to jump across them. So these are some issues with using aluminum. However, aluminum has some great advantages too. It's one of the most lightweight metals. So if you want to build physical enclosures, something that can protect your device that strong but is also very light, you want to use aluminum. It also has less corrosion than copper. So it can resist the elements. So all these things make it really good for cases. In corrosion resistant, wiring in pipes and foils and things like that. It's also a great choice for heat sinks. A lot of heat sinks are made out of aluminum because it's not all that great at distributing heat, is good at radiating it off because it's not very dense. So aluminum is a good choice for these environments. Another choice for a conductor is silver. So of all the metals, silver is the best electrical conductor. It's very good at conducting electricity. Very low resistance. So if you're dealing with environments where you're very battery constrained and you need to transmit electricity, silver is a great choice for that. Silver also happens to be the best thermal conductor as well. So if you have something that's hot, you need to get the heat away from that, you can use silver. Silver has a high melting temperature. So can withstand high temperatures. Unfortunately, it's very expensive. There's a lot of demand for silver and there's not much of it. So that drives up prices up high. Still it's good for environments where you're building things. You're deploying things and you can afford to pay high prices. Silver also has poor corrosion properties, and if you've ever been in a house where someone owns silverware. But that stuff tarnishes, you can have something that's nice and shiny and overtime it'll get cloudy you need to polish it, that's corrosion. Not very good for electrical connections. You have two pieces of silver pointing at each other. That stuff can get in between and damage the connection. So you have to maintain it. However, silver is very reflective. So it's good for things like mirrors and optical components. It's used a lot in optical storage and optical mechanisms. Is also very pliable, and it's very ductile as well. So it's good for, if you're building very thin wires. It's something you can stretch out make very thin things that if you're building intricate things, silver is a great choice for that as well because you can take the silver and platt little tiny things. If you're doing something with steel that's much harder to do because steel is brittle and steel breaks, but silver is great at that. Another choice is nickel. So Nickel is a metal that's very corrosion resistant. It's very strong, and it has a very high melting point. So if you need a material that's very resistant to heat and it's not going to melt if you're dealing with really hot industrial environments, nickel is a great choice for that. Unfortunately, nickel likes to interact with other metals. Which is good if you're trying to form alloys if you want to mix nickel together with other metals that's a good thing. But it's a problem if you have a plate of nickel and you have some aluminum pressed up against it. It's sit in there. Those metals will interact with each other,and it'll form a new metal that on the boundary between them which might be which is not conductive. So there's problems like that. That can happen. Nickel is very catalytic. It like to interact with other things. Nickel is very ductile though. So it's good for intercut components, and nickel has a high resistance to electricity and heat. So it's not something where it's very conductive. But if you have situations where you use it a little extra battery to push electricity through, then nickel can be a good choice. Another option is to use tin. So tin is a very soft metal. Tin is something and if you ever held a tin can, you can squish it. It's a metal where you can bend it pretty easily. Is very soft. Is very malleable and ductile. It has a pretty good durability though. So if you have a tin can, you can try squish it over and over it's not going to break very easily. So it is strong. It has poor corrosion resistance to acids and also very basic materials alkalis. It'll corrode a lot in those environments. However, for water it's great. Tin doesn't corrode much in water. So tin is very good for marine applications. If you're building something that's going to sit next to water, lakes, or oceans. Tin also has a very low melting point. So if you want something that can melt and be malleable and you can work with that at low temperatures, tin is a good choice and actually tin is used a lot in solder to create connections between electrical conductors. Because it's very malleable. Is used for malleable enclosures. If you want to build a something that encloses your system, case and you want to, it's not good to go very rigid things because rigid things break. So tin can be a good choice if you're dealing with an environment where it might get knocked around, you want to have a little flex in it tin is a good choice for that. I also want to mention steel. Steel is actually a very poor choice for a conductor. It has very poor electrical conductivity. We don't really use steel wires to conduct electricity if we can avoid it. It also has poor thermal conductivity not something you want to use for heat sinks. However, steel is really strong we use it to build skyscrapers very powerful very strong and heavy. Steel is also something where it's hard to create shapes out of it. Because it's very brittle. It's strong but if you try and bend it, it will resist bending, it resist bending and it'll just break. So if you want to build shapes out of it or intricate designs, really hard to do that with steel. Steel is also subject to rust and corrosion once exposed to water. If you want to prevent this corrosion, you can coat steel included in a plastic. But if it's exposed to water, it'll corrode. So steel is what you want to use if you want to make your device strong, is good for building reinforcing infrastructures. If you have struts or cables or enclosures, steel can be a good choice for that. So what I've done here is I've given you an overview of the different kinds of conductors you can use in your design. Different metals. So if you're going to choose which wires you're going to use in your design, you now know a little bit more about the different properties of these metals. You can choose between these for your wires or enclosures and so on.