CMOS Sourcebook, by Newton C. Braga (Sams Technical Publishing, 2001)
This book is entirely devoted to the 4000 series of CMOS chips, not the 74HC00 series that I’ve dealt with primarily here. The 4000 series is older and must be handled more carefully, because it’s more vulnerable to static electricity than the generations that came later. Still, the chips remain widely available, and their great advantage is their willingness to tolerate a wide voltage range, typically from 5 to 15 volts. This means you can set up a 12-volt circuit that drives a 555 timer, and use output from the timer to go straight into CMOS chips (for example). The book is well organized in three sections: CMOS basics, functional diagrams (showing pinouts for all the main chips), and simple circuits showing how to make the chips perform basic functions.
The Encyclopedia of Electronic Circuits, by Rudolf F. Graf (Tab Books, 1985)
A totally miscellaneous collection of schematics, with minimal explanations. This is a useful book to have around if you have an idea and want to see how someone else approached the problem. Examples are often more valuable than general explanations, and this book is a massive compendium of examples. Many additional volumes in the series have been published, but start with this one, and you may find it has everything you need.
The Circuit Designer’s Companion, by Tim Williams (Newnes, Second Edition, 2005)
Much useful information about making things work in practical applications, but the style is dry and fairly technical. May be useful if you’re interested in moving your electronics projects into the real world.
The Art of Electronics, by Paul Horowitz and Winfield Hill (Cambridge University Press, Second Edition, 1989)
The fact that this book has been through 20 printings tells you two things: (1) Many people regard it as a fundamental resource; (2) Secondhand copies should be widely available, which is an important consideration, as the list price is over $100. It’s written by two academics, and has a more technical approach than Practical Electronics for Inventors, but I find it useful when I’m looking for backup information.
Getting Started in Electronics, by Forrest M. Mims III (Master Publishing, Fourth Edition, 2007)
Although the original dates back to 1983, this is still a fun book to have. I think I have covered many of its topics here, but you may benefit by reading explanations and advice from a completely different source, and it goes a little farther than I have into some electrical theory, on an easy-to-understand basis, with cute drawings. Be warned that it’s a brief book with eclectic coverage. Don’t expect it to have all the answers.
Figure 5-9. These books from MAKE provide guidance if you want to go beyond basic microcontrollers into the more exotic realms of the Arduino chip.
Figure 5-10. A sun-damaged copy of the Don Lancaster’s classic TTL Cookbook, a 2,000-page catalog from the Mouser Electronics supply company, and two comprehensive reference books that can provide years of additional guidance in all areas of electronics.
Experiment 25: Magnetism
This experiment should be a part of any school science class, but even if you remember doing it, I suggest that you do it again, because setting it up takes only a matter of moments, and it’s going to be our entry point to a whole new topic: the relationship between electricity and magnetism. Quickly this will lead us into audio reproduction and radio, and I’ll describe the fundamentals of self-inductance, which is the third and final basic property of passive components (resistance and capacitance being the other two). I left self-inductance until last because it’s not very relevant to the experiments that you’ve done so far. But as soon as we start dealing with analog signals that fluctuate, it becomes essential.
You will need:
Large screwdriver.
22-gauge wire (or thinner). Quantity: 6 feet.
AA battery.
Fundamentals
A two-way relationship
Every electric motor that was ever made uses some aspect of the relationship between electricity and magnetism. It’s absolutely fundamental in the world around us. Remember that electricity can create magnetism:
When electricity flows through a wire, it creates a magnetic force around the wire.
The principle works in reverse: magnetism can create electricity.
When a wire moves through a magnetic field, it creates a flow of electricity in the wire.
This second principle is used in power generation. A diesel engine, or a water-powered turbine, or a windmill, or some other source of energy either turns coils of wire through a powerful magnetic field, or turns magnets amid some massive coils of wire. Electricity is induced in the coils. In the next experiment, you’ll see a dramatic mini-demo of this effect.
Procedure
This couldn’t be simpler. Wind the wire around the shaft of the screwdriver, near its tip. The turns should be neat and tight and closely spaced, and you’ll need to make 100 of them, within a distance of no more than 2 inches. To fit them into this space, you’ll have to make turns on top of previous turns. If the final turn tends to unwind itself (which will happen if you’re using stranded wire), secure it with a piece of tape. See Figure 5-11.
Figure 5-11. Anyone who somehow missed this most basic childhood demo of electromagnetism should try it just for the fun of proving that a single AA battery can move a paper clip.
Now apply a battery, as shown in Figure 5-12. At first sight, this looks like a very bad idea, because you’re going to short out your battery just as you did in Experiment 2. But by passing the current through a wire that’s coiled instead of straight, we’ll get some work out of it before the battery expires.
Put a small paper clip near the screwdriver blade, on a soft, smooth surface that will not present much friction. A tissue works well. Because many screwdrivers are already magnetic, you may find that the paper clip is naturally attracted to the tip of the blade. If this happens, move the clip just outside the range of attraction. Now apply the 1.5 volts to the circuit, and the clip should jump to the tip of the screwdriver. Congratulations: you just made an electromagnet.
Figure 5-12. A schematic can’t get much simpler than this.
Theory
Inductance
When electricity flows through a wire, it creates a magnetic field around the wire. Because the electricity “induces” this effect, it is known as inductance. The effect is illustrated in Figure 5-13.
Figure 5-13. When the flow of electricity is from left to right along this conductor, it induces a magnetic force shown by the green arrows.
The field around a straight wire is very weak, but if we bend the wire into a circle, the magnetic force starts to accumulate, pointing through the center of the circle, as shown in Figure 5-14. If we add more circles, to form a coil, the force accumulates even more. And if we put a magnetic object (such as a screwdriver) in the center of the coil, the effectiveness increases further.
Figure 5-14. When the conductor is bent to form a circle, the cumulative magnetic force acts through the center of the circle, as shown by the large arrow.
Here’s an approximated formula showing the relationship between the diameter of the coil, the width of the coil from end to end, the number of turns, and its inductance. The letter L is the symbol for inductance, even though the unit is the Henry, named after an American electrical pioneer named Joseph Henry:
L (in microHenrys) =
[(D × D) × (N x N)] / [(18 × D) + (40 × W)]
(Approximately)
In this formula, D is the diameter of the coil, N is the number of turns, and W is the width of the coil from end to end. See Figure 5-15. Here are three simple conclusions from this formula:
Inductance increases with the diameter of the coil.
Inductance increases with the square of the number of turns
. (In other words, three times as many turns create nine times the inductance.)
If the number of turns remains the same, inductance is lower if you wind the coil so that it’s slender and long, but is higher if you wind it so that it’s fat and short.
Figure 5-15. The inductance of a coil increases with its diameter and with the square of its number of turns. If all other parameters remain the same, reducing the width (the distance from end to end) by packing the turns more tightly will increase the inductance.
Fundamentals
Coil schematics and basics
Check the schematic symbols for coils in Figure 5-16. Note that if a coil has an iron core, this is shown with an extra couple of lines (sometimes only one line). If it has a ferrite core, the line is sometimes shown with dashes.
An iron core will add to the inductance of a coil, because it increases the magnetic effect.
A coil in isolation does not generally have any polarity. You can connect it either way around, but the magnetic force will be reversed accordingly (coils that interact with stuff—such as in transformers and solenoids—do have polarity).
Perhaps the most widespread application of coils is in transformers, where alternating current in one coil induces alternating current in another, often sharing the same iron core. If the primary (input) coil has half as many turns as the secondary (output) coil, the voltage will be doubled, at half the current—assuming hypothetically that the transformer is 100% efficient.
Figure 5-16. Schematic diagrams represent coils. At far right is the older style. The third and fourth symbols indicate that the coil is wound around a solid or powdered magnetic core, respectively.
Background
Joseph Henry
Born in 1797, Joseph Henry was the first to develop and demonstrate powerful electromagnets. He also originated the concept of “self-inductance,” meaning the “electrical inertia” that is a property of a coil of wire.
Henry started out as the son of a day laborer in Albany, New York. He worked in a general store before being apprenticed to a watchmaker, and was interested in becoming an actor. Friends persuaded him to enroll at the Albany Academy, where he turned out to have an aptitude for science. In 1826, he was appointed Professor of Mathematics and Natural Philosophy at the Academy, even though he was not a college graduate and described himself as being “principally self-educated.” Michael Faraday was doing similar work in England, but Henry was unaware of it.
Henry was appointed to Princeton in 1832, where he received $1,000 per year and a free house. When Morse attempted to patent the telegraph, Henry testified that he was already aware of its concept, and indeed had rigged a system on similar principles to signal his wife, at home, when he was working in his laboratory at the Philosophical Hall.
Henry taught chemistry, astronomy, and architecture, in addition to physical science, and because science was not divided into strict specialties as it is now, he investigated phenomena such as phosphorescence, sound, capillary action, and ballistics. In 1846, he headed the newly founded Smithsonian Institution as its secretary.
Figure 5-17. Joseph Henry was an American experimenter who pioneered the investigation of electromagnetism. This photograph is archived in Wikimedia Commons.
Experiment 26: Tabletop Power Generation
If you have just three components, you can see magnetism generating electricity right in front of you, right now.
You will need:
Cylindrical neodymium magnet, 3/4-inch diameter, axially magnetized. Quantity: 1. (Obtainable online at sites such as http://www.kjmagnetics.com.)
Spool of hookup wire, 26-gauge, 100 feet. Quantity: 1.
Spool of magnet wire, quarter-pound, 26-gauge, about 350 feet. Quantity: 1. (Search online for sources for “magnet wire.”)
Generic LED. Quantity: 1.
100 μF electrolytic capacitor. Quantity: 1.
Signal diode, 2N4001 or similar. Quantity: 1.
Jumper wires with alligator clips on the ends. Quantity: 2.
Procedure
You may be able to make this experiment work with the spool of hookup wire, depending on the size of the spool relative to the size of your magnet, but as the results are more likely to be better with the magnet wire, I’ll assume that you’re using that—initially, at least. The advantage of the magnet wire is that its very thin insulation allows the coils to be closely packed, increasing their inductance.
First peek into the hollow center of the spool to see if the inner end of the wire has been left accessible, as is visible in Figures 5-18 and 5-19. If it hasn’t, you have to unwind the wire onto any large-diameter cylindrical object, then rewind it back onto the spool, this time taking care to leave the inner end sticking out.
Figure 5-18. An everyday 100-foot spool of hookup wire is capable of demonstrating the inductive power of a coil.
Figure 5-19. Magnet wire has thinner insulation than hookup wire, allowing the turns to be more densely packed, inducing a more powerful magnetic field.
Scrape the transparent insulation off each end of the magnet wire with a utility knife or sandpaper, until bare copper is revealed. To check, attach your meter, set to measure ohms, to the free ends of the wire. If you make a good contact, you should measure a resistance of 30 ohms or less.
Place the spool on a nonmagnetic, nonconductive surface such as a wooden, plastic, or glass-topped table. Attach the LED between the ends of the wire using jumper wires. The polarity is not important. Now take a cylindrical neodymium magnet of the type shown in Figure 5-20 and push it quickly down into the hollow core, then pull it quickly back out. See Figure 5-21. You should see the LED blink, either on the down stroke or the up stroke.
The same thing may or may not happen if you use 100 feet of 26-gauge hookup wire. Ideally, your cylindrical magnet should fit fairly closely in the hollow center of the spool. If there’s a big air gap, this will greatly reduce the effect of the magnet. Note that if you use a weaker, old-fashioned iron magnet instead of a neodymium magnet, you may get no result at all.
Figure 5-20. Three neodymium magnets, 1/4-, 1/2-, and 3/4-inch in diameter. I would have preferred to photograph them standing half-an-inch apart, but they refused to permit it.
Figure 5-21. By moving a magnet vigorously up and down through the center of a coil, you generate enough power to make the LED flash brightly.
Blood Blisters and Dead Media
Neodymium magnets can be hazardous. They’re brittle and can shatter if they slam against a piece of magnetic metal (or another magnet). For this reason, many manufacturers advise you to wear eye protection.
Because a magnet pulls with increasing force as the distance between it and another object gets smaller, it closes the final gap very suddenly and powerfully. You can easily pinch your skin and get blood blisters.
If there’s an object made of iron or steel anywhere near a neodymium magnet, the magnet will find it and grab it, with results that may be unpleasant, especially if the object has sharp edges and your hands are in the vicinity. When using a magnet, create a clear area on a nonmagnetic surface, and watch out for magnetic objects underneath the surface. My magnet sensed a steel screw embedded in the underside of a kitchen countertop, and slammed itself into contact with the countertop unexpectedly.
Be aware that magnets create magnets. When a magnetic field passes across an iron or steel object, the object picks up some magnetism of its own. Be careful not to magnetize your watch!
Don’t use magnets anywhere near a computer, a disk drive, credit cards with magnetic stripes, cassettes of any type, and other media. Also keep magnets well away from TV screens and video monitors (especially cathode-ray tubes). Last but not least, powerful magnets can interfere with the normal operation of cardiac pacemakers.
Here’s
another thing to try. Disconnect the LED and connect a 100 μF electrolytic capacitor in series with signal diode, as shown in Figure 5-23. Attach your meter, measuring volts, across the capacitor. If your meter has a manual setting for its range, set it to 20V DC. Make sure the positive (unmarked) side of the diode is attached to the negative (marked) side of the capacitor, so that positive voltage will pass through the capacitor and then through the diode.
Now move the magnet vigorously up and down in the coil. The meter should show that the capacitor is accumulating charge, up to about 10 volts. When you stop moving the magnet, the voltage reading will gradually decline, mostly because the capacitor discharges itself through the internal resistance of your meter.
This experiment is more important than it looks. Bear in mind that when you push the magnet into the coil, it induces current in one direction, and when you pull it back out again, it induces current in the opposite direction. You are actually generating alternating current.
The diode only allows current to flow one way through the circuit. It blocks the opposite flow, which is how the capacitor accumulates its charge. If you jump to the conclusion that diodes can be used to change alternating current to direct current, you’re absolutely correct. We say that the diode is “rectifying” the AC power.
Make: Electronics Page 32
