1.0 ADVANCE PREPARATION

1.1  List the name: of the course, the instructor's name, and all of the students' names on the whiteboard

1.2  Prepare the following demonstrations:

1.2.1  The AC power demo panel (switches, contactor, variac, thermostat), garden spigot valve; gate valve; an air pressure valve with push-button operation;, home type; salt, six small cups

1.2.2  Transistor board display; tube board display; old vacuum tube receiver (preferably working).

1.2.3  Cutaways of vacuum tubes and transistors.

2.0 Introduction

2.1  Each staff member introduces himself and gives a little background.

2.2  Class Participation. Remember, we want you to ask questions; you can't learn unless you really understand. If you are sincere.....NO question is too simple or too trivial. We want you to think, not just memorize. And….it's very important that you arrive at the class on-time!! We have more than enough information and project work to keep us all busy for the two hours that you're here. If you arrive late, you hold up the class and every one here is cheated out of valuable time. So….please ask your parents early Saturday morning to get you here on time.

2.3  What is a Museum? You know that we are in a museum. Why do we have museums? [to preserve the past; to help us understand the present; ] Our classes connect the history of the day with the inventions that are the subject of the class.

2.4  Why We're Here: In this course, we're going to learn about these things:

2.4.1  Semiconductors. The whole development theory on transistors is based on "semiconductor science." What are semiconductors? How do they differ from conductors? From insulators?

2.4.2  Transistors: The invention of the transistor opened up this vast field of electronics. Its importance can't be overstated!

2.4.3  Vacuum Tube. Before the transistor, we had vacuum tubes for all control and signal generation. They were unreliable, limited life, fragile, power-wasting, space- wasting…..but they did the job!

2.5  Equipment. We have eight workbenches and toolboards; two students work together at each of these benches. It's very important that you treat the bench the same as you would treat the family dining-room table. Never drill directly into it; never solder on it; never pound directly on it. Each bench has a backer board that is used under your work so that the bench will not be scarred or damaged. In addition, for this class, each bench has a digital multi-meter. You will learn how to use this instrument for some of the experiments.

2.6.  Each Workshop Session: Our first hour at each session is spent talking about the history and the theory. The second hour is spent on the workbench, running experiments with your Experimenter's Kit. At the end of this second hour, and before you leave, clean up your work area and put all of your experimental work into the kit box. Check that your name is on your kit; then bring the kit up to my table here. Put away all tools of your workbench color; return any tools of a different color to the proper workbench; clean off the bench and local floor area of scraps, paper clippings, wire ends and any other items that don't belong there. DO NOT LEAVE UNTIL EVERYTHING IS ALL CLEANED UP!!

3.0 THEORY AND DEMONSTRATION

3.1  Control: {Show off the different types of valves] Why did I bring these valves in today? What could they possibly have to do with transistors and vacuum tubes? [a way to control energy]. Can you name anything else that has energy and we have a way of controlling it….turning it on or off, or both ON and OFF? [water wheel and a chute; a stick of dynamite; a bullet in a gun; a horse-drawn wagon; the steam valve on a locomotive; the gas pedal in a car…]. The vacuum tube acts as an electronic valve, controlling energy flow. In fact, the average Londoner wouldn't even realize what you meant if you referred to a "tube". To a Londoner, "the tube" is….do you know what? [the subway system]. They refer to vacuum tubes as "electron valves." This display shows different types of vacuum tubes, starting with old ones of about 1918 and running up to "new" ones in the 1960s.

3.2  Function: What is the basic function of a transistor or a vacuum tube [to control a large amount of power with a small control power]? Why are transistors and vacuum tubes so important? [because they are high-speed controllers in electric circuits] What is an electric circuit? .What did we use for controls before we had transistors or vacuum tubes?. [switches; telegraph key; telephone transmitter mouthpiece; connectors, plugs] Demo: AC Panel, telegraph key and sounder.

3.3  Early History Leading up to the Vacuum Tube: Two hundred years ago, in the year 1800, none of the miracles that we take for granted to day existed, even in brilliant minds.

3.3.1  The battery: It was then that Volta invented the electric battery, giving us a source of electric power. Before we had a battery, where did we get our electrical energy? [rubbing amber on a cat's fur; electroscope; static generating machines].

3.3.2  The electric motor: with steady power, Faraday invented one of the first electric motors. Others went on and quickly, within 20-30 years there was an electric motor that closely resembles today's motors. But nobody cared! Why not? [it ran from batteries, which wore out quickly] We soon discovered that the motor, when run backward from something like a steam engine, would generate electricity. And the race was on!!

3.3.3  The light bulb: This invention was offered in many different forms by different inventors, beginning with Sir Humphrey Davy ca 1803. However, there was no production electric light bulb until 1879. Why not? This is a whole course in itself. Simply stated, Thomas Edison invented the first reliable electric lighting system. He invented the light bulb, the screw-in base just like the ones used today; the dynamo that generated 110 volts. And that's why we have a standard voltage that is used today everywhere in the USA

3.3.4  The Edison effect: In 1883 Edison was testing his light bulbs to learn why there was a black deposit on the inside of the glass. He put an independent plate inside the bulb. While he was making measurements with electric power on the bulb, he observed that a current flowed between the light bulb filament and the plate when it had a positive voltage on it. Did he jump up and say, " Hey, I've invented electron flow."? Absolutely not!! Why not? [No one had discovered the electron yet -- scientists referred to current flow as "a fluid" that moved through conductors." This phenomenon was called "The Edison Effect." Edison paid no further attention to it -- he didn't see it as having anything to do with his problem, and he was very focussed. But it was the first step toward the invention of the vacuum tube.

3.3.5  Discovery of the Electron: Just 14 years later, in 1897, J.J. Thomson of England, in a series of remarkable experiments, identified the "electric fluid" as being a collection of electrons. He further related them to the atom, and even computed a "charge to mass" ratio for the electron.

3.3.6  The first thermionic diode: What do I mean by "Thermionic?" [operated by heat]. In 1904, John A. Fleming made the first radio tube by using the Edison effect. He used a heated wire, resembling a light bulb filament, to release a cloud of electrons. Such an element was called a cathode long before Fleming's work. He then used a second element, called an anode or a plate, to collect the electrons. He discovered that this diode would pass a current when the cathode was negative and the anode was positive; however, it would not pass a current when the polarity was reversed. What do I mean by reversed polarity? [Draw a picture on the board with the voltages]. A device that operates in this manner is called a rectifier. This was the beginning of a development period that involved thermionic vacuum tubes.

3.3.7  Early history of semiconductor research: Long before there was any thought of vacuum tubes, of transistors, of radios….scientists were studying semiconductors. In 1833 Michael Faraday reported on peculiar resistance properties of silver sulfide.

3.3.8  Marconi's first radio. The race to develop semiconductors really started with the beginning of radio, back in the Marconi arc transmitter time around 1895. Marconi's first radio receiver was terribly insensitive! This receiver did not have a loudspeaker, or even earphones. How did Marconi know that his receiver was getting a signal? The signal coming in from the antenna had to be strong enough that it would create an arc -- this is how one knew that the transmitter at the other end was sending.

3.4  Early history of semiconductor detector development. "There must be a better way!"

3.4.1  'Way back in 1874, Ferdinand Braun was experimenting with various sulfide crystals. Much to his surprise, the crystals seemed to conduct much better in one direction than in the other. But there wasn't any such thing as a radio then, and he went on to study other things.

3.4.2  In 1890, Edouard Branly invented an ingenious device called the "coherer". It consisted of a glass tube with a bunch of metal filings inside. The Marconi-style very crude receiver applied a received current to the coherer. This caused the filings to stick together. Problem: they stuck together after the transmitted signal was turned off. The ingenious solution to this was to keep tapping the tube very rapidly to shake the filings down once the transmitted signal was off. It was more sensitive than requiring the sight of an arc, but not much more. And, as you might expect, one could not send Morse code very fast with this system.

3.4.3  In 1897, let's go back and see what Ferdinand Braun is doing. By now, Marconi had done some work on radio transmission and Braun was intrigued. He experimented with coherers for his receiver, but was dissatisfied with their performance and lack of sensitivity. He replaced the coherer with one of his crystals, to run it as a detector of the radio waves. It didn't work very well either! But then, he substituted earphones from a telephone and the receiver became much more sensitive. He now had a good receiver for radio waves!

3.4.4  In 1904 in India, a brilliant scientist named J.C. Bose had also been looking for a good detector. He too tried using a sulfide crystal -- a lead sulfide unit. This spelled the death knell of the coherer. The standard detector now was a crystal and a set of headphones.

3.4.5  And finally, to lead this study of semiconductor detectors and rectifiers into the modern world, there was G.W. Pickard of the USA. He meticulously made a study of over 30,000 different materials to be used for crystal rectifiers. In 1907 he selected silicon crystals to serve in the receivers. Although the Fleming valve replaced the crystal detector when price was no object, the crystal continued as the first choice for the inexpensive receivers.

3.5  Semiconductor Facts:

3.5.1  Comparisons: The semiconductor lives somewhere between good conductors and good insulators. Can you name a few of each? [for conductors: metals, impure water with dissolved salts; for insulators: glass, ceramic, most plastics; dry wood; dry silk; Why can't we just call the semiconductors: "resistors?" [their conductance varies greatly with temperature and bias voltage]

3.5.2  Particular Semiconductors: silicon; germanium; lead sulfide; silicon carbide. Copper oxide; selenium

3.5.3  Atomic Structures for Conductors, Semiconductors and Insulators: a. Conductors, such as metals, have electrons that move around in a "soup" of ions. Very little energy is required to move these seemingly unattached electrons. Semiconductors have a very tight, strong electron bond among the atoms, and the electrons are quite difficult to move. At absolute zero, no electron motion occurs; conduction increases markedly with increases in temperature. Insulators have much tighter, stronger electron bonds among the atoms than semiconductors. Typically, no electron movement occurs until the temperature is raised up to the point of destruction of the material. Any impurities typically will degrade the insulation.

3.5.4  Uses of Semiconductors: Some of the first uses were for detectors for radio receivers. For homes and factories wired with electric power (ca 1895 - 1940), the semiconductors are used as rectifiers to do a variety of electronic functions. They are also used in electronic thermometers; as lightning arrestors; as energy protectors in computer systems. Even more important is the use of semiconductors as the building material for making transistors and integrated circuits.

4.0 WORKSHOP HANDS-ON SESSION

4.1  You will work at our workbenches, with two students at each bench. Be considerate of each other, and do NOT monopolize the bench space. At the end of each session, pick up all of the material from your experimenter's kit and replace the kit in the box. Clean up the bench of any paper, wire scraps, or whatever. Remember the signs that some of us used to see in our laboratory: "Your mother doesn't work here! Clean up after yourself!".

4.2  For this class, we are doing something different from all of our earlier classes. Instead of having one project to build, we are going to work with an electrical experimenter's kit. Each of you will receive a kit. It is your property, and you will take it home at the end of our last, or fourth, meeting. We have a choice of over 50 experiments to perform, each of which gives you a chance to learn another bit about electricity, transistors, and semiconductors. As soon as you receive the kit, you must write your name in three places: 1)..On the outside of the Kit, at one end so that we can see the name when the boxes are stacked; 2) On the underside of the experimental board, so that there is no doubt who owns that kit; 3) On the front cover of your instruction manual.

4.3  Our session today will work with experiments nos. 1 through10. The instructors will help you with these experiments. For those of you who finish early, go ahead and start the next experiment. However - remember - this is not a contest!! We want you to understand what you are doing on each experiment; be sure to read all of the instructions that go with each of the experiments.

4.3.1  Experiments 1 through 10 are about LEDs, resistors, capacitors, and Ohm's Law. Be careful to read all of the explanation that goes with each one of these experiments. Note that the 9-volt battery must first be installed. Look at page 8 in your book to see how that is done.

4.3.2  There is a circuit diagram for each experiment. Follow that diagram to connect the wires. Note that each connection point is numbered. You put a wire to each point. Use the shortest possible wire for each point, so that you don't have a sloppy mess of wires hanging over the board. Each wire is installed by first bending the spring to one side. Look at page 8 for how to do that.

4.3.3   DMM ( Digital Multimeter) - Each bench has a DMM for use in these experiments. The DMM can indicate a number of different values. You can set it to read voltage, current, or resistance. It can read both dc (direct current, coming from a source such as a battery, or ac (alternating current). We do not work with ac in this class.
The meter has plug-in test leads. The black lead plugs into the "common" port,, and the red lead plugs into the appropriate red port. For your work today, you will plug the red lead into the "Ω-V" , which stands for ohms (resistance) or Volts. You will set the meter dial pointer to the green "V" area marked "20", This "V" has a bar and a dotted line above it, to indicate dc measurements.. You are now ready to read up to 20 volts full-scale.

Note that the meter has some letter designations along with the numbers. These letters are a very important part of the measurement. Here's what they mean:

k = kilo (1000 times the value indicated on the LCD [what's that?]

m = milli ( 1/1000 of the value indicated )

M = mega ( one million times, or 1,000,000 times the value indicated

u = micro (one millionth of, or 1/1000,000 of the value indicated)

4.3.4  Measuring resistance - you can also use the DMM to measure resistance. First, -- and very important!! -- Be sure that the battery is not connected, If you have the battery switch properly connected, that's good enough. Set the dial to the "Ω" area. To read a resistor that is less than 1.0 Kohm, set the dial at "2" If the resistor value is greater than the dial reading ( for instance, "3K") the meter will show "1 ." .

4.3.5  Page 7 of this session is "First Session Laboratory Experiments. These experiments, using the DMM, are done at the same time that you are doing Experiments 1 and 2. Take the measurements across the test points shown, when you are pressing on the battery switch.

4.3.6  After you have finished this set of experiments, do the quiz on page 24 and bring your notebook to the instructor for checking.

Ohms Law: E = I R or I = E / R or R = E / I

Experiment 10 - Put the meter across the 100 uF capacitor (36, 37). You can now watch the voltage decay. Note that it slows down below about 1.5 volts. What happens at that voltage?