AE-230 / 231 / 252
INSTRUCTOR: Eddie CilettiWEEK-1: Introduction to Electronics
Day-1
I had this idea to use a string of lites to show the difference between Conventional Current Flow (plus to minus) and Electron Flow (minus to plus). Here goes..
You might be wondering what actually happens when you turn something on. Everything that matters is MATTER and it's composed of atomic particles - protons, neutrons and electrons.
As the ancient geeks were stumbling upon the basic building blocks - like generating and measuring electricity - they had to "guess" when assigning POLARITY, like POSITIVE and NEGATIVE. They had a fifty-fifty chance of getting it right (they didn't), consequently, we have two ways at looking at how current flows. CONVENTIONAL CURRENT flows from plus to minus - that's what the ancient geeks thought. Later, once everybody had test equipment that could assist in deciphering the laws of physics. It was determined that electrons were doing the moving and shaking during the "current dance."
So, take a look at the sting of lights. Electrons are in BLUE, moving from right-to-left. Holes are in black and move from left to right.
I got this overview of "Holes" from Wikipedia...
In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. A full (or nearly full) valence band is present in semiconductors and insulators. The concept of a hole is essentially a simple way to analyze the electronic transitions within the valence band.
Hole conduction can be explained by the following analogy. Imagine a row of people seated in an auditorium, where there are no spare chairs. Someone in the middle of the row wants to leave, so he jumps over the back of the seat into an empty row, and walks out. The empty row is analogous to the conduction band, and the person walking out is analogous to a free electron.
Now imagine someone else comes along and wants to sit down. The empty row has a poor view; so he does not want to sit there. Instead, a person in the crowded row moves into the empty seat the first person left behind. The empty seat moves one spot closer to the edge and the person waiting to sit down. The next person follows, and the next, et cetera. One could say that the empty seat moves towards the edge of the row. Once the empty seat reaches the edge, the new person can sit down.
In the process everyone in the row has moved along. If those people were negatively charged (like electrons), this movement would constitute conduction. If the seats themselves were positively charged, then only the vacant seat would be positive. This is a very simple model of how hole conduction works.
BUILDING A CIRCUIT, ONE COMPONENT AT A TIME
There are a handful of Electronic Components that can be configured into basic building blocks - useful circuits that must first be "turned-on" to be in a useful state. The most obvious example, for our purposes, is an audio amplifier. It is neither fully ON nor OFF, but "biased" to an in-between "static" state state so it is then ready to be dynamically modulated by an AC (alternating current) audio.
There are AC and DC power sources (such as wall power and batteries), Passive Components (resistors, capacitors, switches, lamps and fuses), Active Components (vacuum tubes, transistors and Integrated Circuits or ICs, the latter being the result of component miniaturization).
Click For Schematic Symbol Exercise
AC signals can be Audio, Radio Frequency (RF) or Power. DC signals can be Power (from batteries or power supplies), control or logic signals. In any electronic circuit, DC is required to turn the active components on via passive components that establish and "center" the operating paramters. The essence of circuit design is for ALL components to operate within a safe "window," from the obvious - not too hot as to compromise longevity - and the less tangible - not too "cold" as to be unpredictable.
Click For Basic Schematic Exercise
Circuits can be analyzed in both the virtual and the real world, on "paper" and with test equipment, respectively. There are a handful of formulae, such as Ohm's Law and the Power Formula, that can be used to establish and analyze the operating parameters.
A digital multimeter can be used to measure "Potential" (in Volts), Current (in Amperes), Resistance (in Ohms) and Capactance (in Micro-farads). Its pedecessor was an analog VOM (volt-ohm, milliamp meter), still in use today.
Prior to the VOM, meters were application-specific - capable of measuring one quantity only (volts or amps, for example). A Wheastone Bridge was used to measure resistance only..
DAY-2Voltage Division: Introduction to Series and Parallel Circuits
Resistors, Light Bulbs (Incandescent Lamps) and Bungee Cords have "resistance" in common. In conventional track lighting, all lamps are in parallel and independent of one another in the sense that one lamp can burn out without affecting the others. Adding another lamp merely increases the illumination, again, without affecting the others.
In a string of "holiday" lights, the lamps are all in series - if one lamp is removed, ALL lamps go out. Oddly, one or more lamps can burn out and the rest stay lit because an internal resistor is in parallel with each lamp filament. This design allows the user to find the bad lamps before the whole string goes out. This happens if too many lamps burn out, stressing the hiddent resistors into failure.
The Bungee Analogy helps to explain what it feels like to be a filament. Stretch a bungee for as long as possible and you will warm up - that's what happenes when electrical current flows. A filament is literally white hot when voltage is applied to it. Imagine the ceiling and the floor as the difference in potential voltage, let's say one-volt per foot, for a distance of ten feet. Now, imagine an eye hook in both locations to which a single bungee is stretched. Pretty taut, eh?
Now, connect two bungees of equal elasticity in series between floor and ceiling. Where do they meet? In the middle, of course, dividing 10-volts in half. The bungees are now half as taut as one signle bungee was. If each was a 100-watt light bulb, they'd now be operating at 50-watts.
CLICK for Voltage Division Exercise
Ohm's Law is one example of how math can describe what happens to electrons as they make the journey from power source to components and back It is ALWAYS a round trip, what is referred to in wiring as Continuity.
Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere. Students should know two primary formulae - Ohm's Law and the Power Formula - from which they can derive all the others.
This image courtesy of the12volt.com
This image courtesy of the12volt.com
READING and LINKS
