Video Projects and Demos
- Electrical Components: Discussion
- Digital Logic: Gates
- Networking - pending
- Computer Programming - pending
- Microcontrollers - pending
When we think about electricity and electronics the first thing that comes to mind is switching things. We have light switches in our houses and we are switching on and off gobs of stuff in our daily lives without ever stopping to think what it is we are really doing - controlling energy by allowing electrons to flow or not. To understand what’s going on, we have to know about what conducts electrons and what doesn’t, and also the concept of a circuit.
It’s nice to know a lot about the Periodic Table to determine how various materials might be used with electricity, but being modern humans, we already know a lot by association. We are aware lighting circuits use mainly copper as a good material to conduct electrons. The main reason copper has widespread use is because it’s cheaper than the alternatives like silver and gold. Aluminum has been used as a conductor for households with a disastrous results by causing fires from an elusive property called “creep.” Over time an electrical connection comes loose as the metal changes shape under the pressure of the terminal. The resulting arcing causes excessive heat. In a wooden house, that’s trouble. We also have to confirm electrons won’t move at all without a completed circuit from a source back to that source - Conservation of Energy Law. Along the way, energy can be consumed, but it will always adds up to the energy provided. In our example, energy is consumed or better explained as energy mostly transformed, when a light comes on. A few years ago, that meant a filament got so hot it would emit light as electrical energy was being converted into heat. Today much more complex energy transforms are being done with fluorescents and LEDs or halogen gas plasmas to light things up. But it all stems from the chemical properties described in the Periodic Table. Copper is a conductor, because it has a loosely tied electron in its outer shell. Maybe I said too much… Yes, atoms have various shells of electrons buzzing around, each balancing out atomic forces. If a material has one or two electrons in its outer shell, those are easily moved by magnetic and static electric forces.
Nature balances energy transfers by manipulating the amount of electrons moving in a wire of copper or other conductive material by providing a resistance to the flow, so as more energy transfers, the amount of electron flow or current increases proportional to the force causing the migration and the resistance to the movement. What provides the potential energy in the first place is called voltage in electric circuits. This potential energy comes, once again, from the material properties of the Periodic Table. Placing various metallic metals together causes an electrical static force to be present. If we stack these elements to form a battery of them, thus the name battery, the force increases. For direct current scenarios, voltage is like pressure in a water pipe where the amount of water flowing is equivalent to current (measured in amperes) and the pipe diameter is equivalent to resistance measured in ohms in an electric circuit. Or better yet, if a restriction is placed in the pipe, a resistance to the flow is seen discretely like a resistor in an electrical circuit. In a water circuit, the pressure is provided by gravity or a pump.
When we restrict current in a circuit, the first energy transformed is usually heat, depending on the efficiency of the electronic component. So why do we care? Excessive heat usually destroys components. But more surprising is the amount of heat or energy transferred, goes up as the square of current flow. If we don’t become savvy to circuit parameter effects, things blow up or burn out quickly.
You might be thinking, I just want to take the trip; I don’t need to know how the train engine works to get there. True. But what if our task at hand is to build an engine so we can make the trip. What I will be doing here is teaching engineering, not selling vacations. But through examples, it should be a fun ride. So let’s go.
Moving electrons has another very unusual property and that is they produce a magnetic field. This phenomenon is very useful and makes possible motors, generators, and the type of power we use to run our homes and businesses. Since magnetism is invisible in itself, it can take on some mysterious effects. If you pass a conductor through a magnetic field, electrons are forced to move in the conductor in a predetermined direction established by the magnetic field, which has the opposite effect when we pass electrons through a conductor which produces a magnetic field in a particular polarity associated with the direction the current is flowing. So our job is to figure out which way the current is flowing to produce a magnetic field so that we can also label its polarity for a better term. Getting directions and polarities confused is easily done, so keeping a glossary of terms is a great thing to do. Will always have Wikipedia as a backup, but tailoring our vocabulary of technical terms keeps us focused on our little corner of the world and group things logically about what we are learning. The art of being educated is growing a vocabulary and referencing what these terms mean. We use words to think with, and words can have connotations, so writing down what the best definitions are for terms you are using at the time, is a smart thing to do. Next, compare with other trusted sources to see what the variations might be. That can be enlightening as well. Back to the elusive electron.
Electrons can generate an influence on conductive materials by just standing still, but accumulating beyond what the material needs to be atomically stable. This is how a capacitor works. Two conductive surfaces are brought close together with a dielectric material in between that has the property to store electric charge equivalent to the energy placed across the material. A dielectric is a material that basically is an insulator, but under electric stress becomes polarized and its molecules align with the electric field and stay that way until the electric field is reversed or dissipates. At that point, electrons are allowed to flow in the external circuit to bring the material back to an unpolarized state or even reversed. The exciting thing is, the resistance of these devices is very low, and if the circuit connected has low resistance, the current tries to reach an uninhibited level very fast only limited by the native resistance in the wiring. Engineers categorize capacitors as devices that store electrical charge not unlike a battery, but can flip polarities in many types in such a manner that alternating currents appear to pass right through them, a property we will find very useful in later discussions. Note the symbol for a capacitor is two parallel plates, but they are not touching.
If we take a copper wire and wrap it into a coil, in effect, the coils of wire will multiply the magnet field while storing energy in a magnetic field like capacitors store electric energy in their dielectric material. The resistive effects are everywhere, but when concentrated to get desired electrical outcome, we call those devices resistors. I’ll talk about active devices next like transistors, but with various combinations of the components mentioned so far, we can build up all the various devices known as electronics. What we are doing is controlling energy transfers and transformations.
Active devices are a result of using capacitance, resistance, and inductance to form switches, amplifiers, comparators, timers, and digital logic. They’re better known for performing a function more than presenting electrical properties based on electron flow.
Transistors are formed from two junctions of semi-conducting material that have been doped with material that allows one to pass electrons easily and the other to accept electrons, but are otherwise stable materials. Pushed together, they form a polarity barrier and no electron flow occurs. Here's a good point to mention that like charges repel and unlike charges attract. You probably already knew that, but it’s important here, because this junction barrier is formed by the semiconductor material’s electrons pushing away from the junction. When a tiny current is introduced into the junction, these materials causes a much larger flow of electrons but in a proportional fashion as this barrier is reduced. In other words. The output varies over a much greater range than the input signal thus the input is amplified. If we turn the input on quickly to its maximum point, the output looks like it is being switched from off to full on. If we take a bunch of these switches and arrange them in particular ways, we can produce AND, OR, NOR logic or invert, store digital 1 or 0, multiplex inputs, oscillate to build clocks and timing circuits, etc.
It’s probably a good time to focus on the concept of analog and digital for a moment. The “real world” is analog. In other words, everything varies over a continuum verses snapping on and off. Temperature, humidity, pressure are obvious examples. But most everything continuously moves around and produces varying signals if measured with an electric circuit. Digital systems use switching to represent the “real world” mathematically or compare the relative levels of one signal to another. Our decimal numbering system, based on powers of 10, is so engrained we don’t give it much thought. It’s used to mathematically model everything in science and engineering to have a way to analyzed the “real world.” Electronics can provide switches, but they are either on or off. The magic happens when we use two states, or binary, instead of 10 states as a numbering system. Both are numbering systems, binary just has a lot more digits to represent the same number. Digital switches are very tiny, and computers are very fast, so if we translate our normal mathematical world using decimal to binary, the results are the same in both math models, but now we can use computing power to control not only analysis of data, but control systems with valves, power switches, motors, and virtually everything around us in a predictable way by just using the capabilities of switching things on and off. We can even measure analog signals by assigning a binary number to individual levels of the measured signal. It’s not exact, but very close. If we use a lot of digital measurements in very short intervals, we can read an analog signal with excellent fidelity. We can also produce an analog output by controlling an amplifier with our digital data and filtering the output to smooth it out. This is how CDs and DVDs actually work. Sound or video, in an analog form, is digitized and recorded onto a plastic disk as digital data of long and short pits burned into the plastic disk to encode the off or on state, then reversed by reading the data and sending it to a DAC or digital to analog converter and filtered to see and hear the results. Nowadays video systems are digital from the light sensor all the way to final display on a flat-screen. Digital processing is so ubiquitous, we forget about the analog world. That’s ironic, since the “real world” is analog. All of these processes are happening faster than our senses can detect the changes, so we feel like what we see and hear is analog or a very close approximation.
So in effect, much of electronics has become the ability to move digital data around and storing it to be used for analysis, system control, communication or entertainment. At first, parallel lines were used to move a set of digital bits around, because it was fast, but when computers became so fast, a huge cost savings could be realized if data was serialized and sent over one circuit. So this is where we will begin - serial interfaces.
Although, using an Arduino to manage circuit electronics can enhance what I'm about to describe here, most of the following concentrates on TTL or CMOS dip-package chips, which are small bundles of gated logic arranged to do specific jobs. These chips are still the backbone of prototyping electronic projects, some 40 years after EE's first started piecing together what quickly exploded into the computer age. What surprised me is the parts I first used as a young engineer are still being made in abundance and are fun for the hobbyist where most parts are sub-microscopic and hard to use. DIP packages are large enough to build up without a lot of fuss and have all the functional power you need to run some very complex projects. I yield to the fact that once you know what you want to do, using parts that compress all this logic power into small packages, like the typical microcontroller, makes a lot of sense, yet many functions are still better suited to be built up as separate running pieces of your project. Microcontrollers in conjunction with TTL logic is one step below pushing all your logic into a FPGA and placing the whole circuit inside a postage stamp sized area. Most of us can't build such tiny devices, but using DIP chips and a breadboard, we can do a lot and not loose any computing power.
To illustrate what I mean by "abstraction", I'll build a box of logic that does one thing - help a lead sheep get his flock to grass and water in time of crisis. Say what? First we have to come up with criteria that describes all the parameters of our challenge and then make a "truth table." From the truth table, the needed logic gates will emerge. We'll build the prototype breadboard to checkout the circuit, and then solder up a box to illustrate the point... "It's just a box of switches, until you the designer, abstracts to the user what it is good for." But first, we need to become familiar with the gates.
Click here for Logic Gates.
Click here for the Sheep Compass.
Click here for 555 Timers.
Click here for Hardware Debounced Switching.
Click here for Linear Feedback Shift Registers.
Click here for 7-Segment Display Drivers.