We're in section 1.4, addressing system connectivity. Electronic systems require connections between the various components making up the system. Several methods are used. The first is wires, and then printed circuit board traces, infrared links, fiber-optic links and radio links.
The first one we'll look at is wires. Conductive wire is the most well known method for providing electrical connection between electronic parts. Conductive wire is usually made of copper, gold, silver or aluminum. These are all highly conductive substances. The wire is usually solid or stranded. Here we have a picture of a solid strand, you'll notice here we have a single conductor and it's a piece of solid metal and we have it wrapped with insulation. Then this lower wire- similar with the insulation except that we have strands, many braided conductors here other than this single core conductor.
There are advantages and disadvantages of each, and it tends to be based on application, we won't go there now, in chapter three we'll provide a great deal more detail about the specifics of wire. For now we are just mentioning it as one of the methods for system connectivity.
Printed Circuit Boards
Another is printed circuit boards, and earlier in this chapter we had seen this same graphic here, but one of the methods for connecting devices is through these little things we call traces, and remember we talked about how traces can be on multiple layers of electronic boards. Now the thickness of these traces is usually between .007 to .0028 inches. That is quite thin. The width is going to be a little bit larger, that is usually between .006 and .2 inches.
You can see on this board, for example here, you can see that this trace is really quite wide and here it's quite narrow, and sometimes they get extremely narrow, all the way down to six thousandths of an inch.
Then we have infrared. Many electronic systems pass data through infrared transmitters and receivers, and up here you'll see we have a picture of a transmitter and a receiver, and you'll see these little dotted lines are indicating the actual infrared signal that's being passed from one to the other. And you have a picture of this in your text by the way. Devices that use infrared include: cordless computer mice, this is prior to the advent of the infrared mouse, they were all mechanical, the cordless type are quite nice because the dirt doesn't get clogged up in the little and they're a little more responsive, I like them. And then we have the television remote control, and another thing we call the PDA- Personal Data Assistant.
Now infrared devices, one of the things that identifies them is that they are often referred to as- notice this- “Line of site devices” since the signal cannot penetrate walls or long distances. If you've noticed when using a remote for a remote TV, if someone gets in front of you and you click it you simply won't get a response, or there's a glass or something in your way the TV won't respond, and this is because they are “line of site devices”. Typically short range, although your text doesn't mention it infrared devices usually are operating in the terahertz frequency range.
Fiber Optic Links
Then we have fiber optic links, another method of connectivity of electronic devices. Fiber consists of thin glass threads which have a dense clear inner core- notice here the darker blue is the core, this would be the actual glass- with a less dense outer covering called the cladding- and here you see the outer material here surrounding the glass is the cladding. The fiber moves data as short pulses of light- and you see these arrows here are indicating the actual light moving through the glass core.
The advantages of fiber optic cable is that it can carry much more data than its copper counterpart, so for years copper has been the primary method of moving data but with fiber optics we can more much more data. And it is immune from Electro Magnetic Interference (EMI), now this EMI is the big enemy of copper, because when you're moving data through a copper line and if that wire passes through an area where there is, for example, high voltages or magnetic fields, that data is subjected to being corrupted. And with fiber that data can move right through those magnetic fields or those high noise areas in terms of voltage and it will ignore them, and so light is immune to electromagnetic interference, which is a major advantage of fiber. And it can carry data much further without the need to re-amplify, with copper these devices called repeaters are necessary because copper can only carry data limited distances before it needs to be re-amplified, and fiber can carry it miles, and with copper you're talking several hundred feet at the most.
Now those are the advantages. Disadvantages is that it can be quite expensive and it is rather difficult to install; it is rather delicate, remember it's glass, if you bend it too severely it can break, and it it does in fact break it really requires high-end, extremely expensive equipment to repair it, whereas copper is relatively simple to repair, fiber is extremely difficult to repair.
Okay, radio links; wireless communication is made possible by radio links, the RF spectrum makes possible a wide variety of wire devices to include (and this is not all encompassing but just a few are the things that the RF spectrum makes possible) we have wireless telephones these days, we have wireless networks, paging systems, internet access via satellites, and many forms of industrial control without the need for wires, so these industrial control devices are controlled wirelessly. And I have a picture here, this is a wireless router and this would enable wireless network and these operate, this particular one, about 2.4 gigahertz, and typically devices in the RF spectrum are megahertz and gigahertz ranges, whereas infrared ranges are way up in the terahertz range.
Okay, so this section is rather quick, it addresses system connectivity and we're looking at how are electronic system connected and we looked radio link, fiber optic links, infrared links, printed circuit boards and wires.