Make: More Electronics (2014)
I made suggestions about a work area, storage of parts, tools, and other basics in Make: Electronics. Some of these suggestions should now be revised, while others must be reiterated or elaborated.
Most of the circuits in this book can be powered by a 9V battery, which has the advantage of not only being cheap but also supplying a stable current without any spikes or glitches. On the other hand, the voltage from a battery will diminish significantly with use, and will vary from moment to moment, depending on how much current you are drawing from it.
Having a variable power supply capable of delivering 0VDC to 20VDC (or more) is a real pleasure, but may cost more than you are willing to spend. A reasonable compromise is to buy the type of AC adapter that plugs directly into the wall and has switch-selectable voltages, as suggested in my previous book.
Another option is to buy the kind of single-voltage AC adapter designed for laptop computers. Many have an output around 12VDC, which can be passed through a voltage regulator to get the 5VDC or 9VDC that you need for most of the experiments here. Voltage regulators cost less than $1 each, and a laptop power supply shouldn’t cost much more than $10, making this an attractive option. The power supply should be capable of delivering up to 1A (1,000mA).
You may be tempted to use a cellular phone charger, especially if you have one lying around after a phone has died. But most chargers deliver only 5VDC, which makes them unsuitable for the 9V projects that I will be describing. Also, because they are designed to function as battery chargers, they may reduce their output voltage, depending on the load.
The bottom line: if you’re on a tight budget, and you don’t expect to make permanent versions of any of the projects here, a 9V battery will do. Otherwise, look for a 12VDC adapter in your price range.
Many of the experiments will require a regulated supply of 5VDC. You will need these components:
§ LM7805 voltage regulator
§ Ceramic capacitors: 0.33µF, 0.1µF
§ Resistor: 2.2K
§ SPST or SPDT switch of PC-mount type (i.e., its leads will push into the holes in a breadboard)
§ Generic LED
Figure 3 shows how the parts can be squeezed into the top few rows of a breadboard, creating a positive bus on the left and a negative bus on the right, which is the layout I’ll be using for many experiments. The photograph shows a 9V battery, but naturally you can use an AC adapter. Make sure it has a DC output of at least 7VDC. To avoid generating excess waste heat, the adapter should not deliver more than 12VDC.
Figure 3. Placement of components to provide a regulated 5VDC power supply.
Figure 4 shows the same circuit in schematic form. The capacitors should be included even if you are using a battery, because they insure correct behavior of your voltage regulator.
Figure 4. Schematic for the 5VDC regulated power supply.
I’m suggesting that you include a switch and an LED because they’re so convenient. When you’re wondering why a circuit doesn’t work, it’s useful to see the LED glowing, confirming that power is reaching the board. And when you’re moving wires around to modify a circuit, you’ll appreciate being able to switch the power off and on without any hassles. I’m suggesting a relatively high-value 2.2K resistor in series with the LED, to conserve power if you use a battery.
In Make: Electronics I used the type of breadboard with a pair of buses down each of its two long edges, so that you had positive and negative power on both sides of the board. In this book I decided to use the simpler type of breadboard, which has only one bus down each long edge, as shown in Figure 5.
Figure 5. The external appearance of a breadboard of the type that has only one bus on each side. All the circuits in this book will be designed for this type of board.
I have several reasons for making this change:
§ Boards of this type are exceptionally affordable, especially if you buy them direct from Asian sources that list their products on eBay. Don’t be disconcerted by obscure vendor names such as “herofengstore” or “kunkunh.” At the time of writing, you can find breadboards for as little as $2 each, so long as you don’t mind waiting ten days or more for international shipping. For more advice about component sources, see Appendix B.
If you buy several breadboards, you can keep previous circuits on some of them while using a fresh board for each new circuit.
§ If you want to make a permanent version of a circuit by soldering components into a printed-circuit (PC) board, the easiest way is to use a PC board where the traces are configured in breadboard format. This type of PC board often has just one bus on each side. (The RadioShack 276-170 is an example.) Transferring the components to it from a breadboard will be much easier if the layout is exactly the same.
§ Feedback from readers has shown me that people tend to make mistakes more easily on breadboards where positive and negative buses are paired on both sides. These mistakes can be costly and inconvenient, as some components have very little tolerance for reversed polarity.
It’s important that you always have a mental image of the conductors inside a breadboard, so I’m including a version of a diagram that you may remember from my previous book. Figure 6 shows a cutaway view.
Figure 6. A cutaway view showing the conductors inside a breadboard.
Remember that many breadboards have buses with one or two breaks in them, to allow you to use different power supplies in different sections of the board. I don’t expect to make use of that feature, so when you get a new breadboard, you must use a meter to check that each bus is continuous from beginning to end. If it isn’t, you need to bridge the gaps in the buses with jumper wires. Forgetting to do this is a common cause of nonfunctional circuits.
Once in a while, a reader will send me an email with a photograph of a breadboarded circuit, asking me why it doesn’t work. If the reader has used the flexible type of jumper wires with a little plug at each end, my answer is always the same: I cannot offer any advice. Even if I had the circuit in front of me, I still wouldn’t be able to offer advice, other than to pull out all the wires and start over.
Breadboard jumper wires are quick and simple to install. I have succumbed to their temptation myself, many times—and have often regretted it, because if you make just one error, you will have extreme difficulty finding it amid the wiring tangle.
In almost most of the photographs in this book, you’ll find that I only use plug-type, flexible jumper wires when I need to connect with devices off the breadboard. On the breadboard I use little pieces of solid wire, stripped at each end. They are infinitely easier to deal with when you have to do some troubleshooting.
If you buy ready-cut segments of solid wire in a kit, you’ll find that they are color-coded by length. This is not helpful, because I want my breadboard wires to be color-coded according to function. A connection terminating at the positive bus of the breadboard should be red, for example, no matter how long or short it is. Two wires of equal length that run close together should be of contrasting colors, so that I don’t confuse one with the other. And so on. This way I can look at a breadboard, quickly assess its function, and find a misplaced wire more easily.
Perhaps you feel that custom-cutting your own color-coded jumper wires is too much of a hassle. If so, I have a suggestion. Figure 7 shows the system that I used to breadboard all the projects in this book.
First remove an arbitrary amount of insulation (a couple of inches) and discard it. Next, estimate the distance that your jumper should span on the breadboard. I’ll call this distance “X.” Measure this on the remaining insulation on your wire as shown in Step 2, and apply your wire strippers in the position indicated by the dashed line. Push the insulation down toward the end of the wire, as in Step 3, stopping about 3/8” from the end. Cut on the solid line. Bend the ends, and you’re done.
Figure 7. A simplified way to create breadboard jumper wires.
For sorting and storing jumper wires after they have been cut, you can make yourself a wire-length gauge. This is also useful for bending wire ends to the desired length. It consists simply of a triangular-shaped piece of plastic or plywood with steps cut into the diagonal edge, as shown in Figure 8 and Figure 9. Because the wire thickness will add slightly to the length of the jumper, your gauge should actually use steps that are about 1/16” less than the length that they represent.
Another way to check the lengths of jumper wires is by comparing them against a piece of plain perforated board (often referred to as “perf board”) where the holes are spaced at intervals of 0.1”.
Figure 8. A homemade wire-length gauge for breadboard jumper wires.
Figure 9. A jumper of 1.1” in length being checked against the length gauge.
Remember, holes in a breadboard are spaced 0.1” apart, horizontally and vertically, and the channel down the center of a breadboard is 0.3” wide.
As for wire thickness, I think 24 gauge is by far the best choice for breadboarding. If you use 26 gauge, it tends to kink too easily when you’re trying to push it into the holes; and after it’s inserted, it sits too loosely. On the other hand, 22 gauge is too tight a fit.
You can often find surplus lots of wire on eBay, or from sources such as Bulk Wire. Personally I have ten basic wire colors: red, orange, yellow, green, and blue (the spectrum), and black, brown, purple, gray, and white (the shades). If you are systematic, and you assign one color for each purpose on all your breadboards, this will make your life a lot easier.
Lastly, please take another look at Figure 2 to remind yourself of the two most common breadboard wiring errors. You may think that you would never make such obvious mistakes, but I have certainly made them myself when I’ve been tired or working under deadline.
In Make: Electronics I mentioned “minigrabbers” that you can push onto the probes of a multimeter. These used to be relatively difficult to find, but are now readily available from sources such as RadioShack (catalog part 270-0334, described as “Mini Test Clip Adapters”). Figure 10 shows a black grabber installed on a meter probe, while the red grabber remains unconnected. I think this is a useful mix. You can hook the black grabber onto any ground wire, then use the red probe to detect voltages around a circuit. The grabber is a very tight push-fit, which I think should add only an ohm or two at most.
Figure 10. Minigrabbers convert one or two probes of your meter so that they will latch onto a wire, freeing you from holding a probe in place.
The mechanism of the grabber is shown in Figure 11, where it is in its open state, extended against an internal spring. In Figure 12, the spring has been released to hold a resistor lead.
Figure 11. A minigrabber with its grabbing clip extended against the force of an internal spring.
Figure 12. When the spring is released, the grabber exercises a firm grip on a thin object, such as a resistor lead.
Jumper wires with an alligator clip at each end (as shown in Figure 13) can be used as a substitute, with one alligator gripping a meter probe while the other latches on to a convenient location in the circuit. You’ll find that I mention this later in the book where you need a free hand that isn’t occupied pressing a probe against a wire. Personally I think grabbers are better, but if you don’t want to encumber your meter probe(s) on a semipermanent basis, the double-alligator jumper is an alternative.
Lastly you can buy jumpers that have a micrograbber at each end, as shown in Figure 14. Here again RadioShack is a source, with part number 278-0016 identified as “Mini-Clip Jumper Wires.” The advantage of these jumper wires is that the micrograbber (a size smaller than the minigrabber) can latch onto small parts where an alligator clip would be liable to nudge an adjacent wire and cause a short circuit.
Figure 13. This type of jumper wire with an alligator clip at each end can be used as a “grabber substitute,” with one alligator gripping a meter probe while the other grips a wire or connection in a circuit that is being tested.
Figure 14. A jumper wire with a micrograbber at each end is useful for locations where a full-size alligator clip would be liable to touch an adjacent conductor.
For storing capacitors, the reduced size of multilayer ceramics means that my recommendations in Make: Electronics are becoming obsolete. Tiny parts are most efficiently kept in tiny containers, and jewelry hobbyists have exactly what we want.
At a crafts store in the United States, such as Michael’s, you will find all sorts of clever storage systems for beads. The system I use now for multilayer ceramic capacitors is a bead storage box shown in Figure 15. Ceramic capacitors fit easily into these little screw-top compartments, which are only 1” in diameter. This enables me to keep an entire range of basic values on my desktop, from 0.01µF (10nF) upward, in a box measuring just 6.5” by 5.5”. Moreover, because each container has a screw top, if I accidentally drop the whole box on the floor, the capacitors will remain confined instead of scattering everywhere. This is important because capacitors look so similar, it would be a nightmare trying to separate them by value.
Figure 15. Modern multilayer ceramic capacitors are so small, storage containers designed for beads are ideal.
For resistors, I suggest cropping their leads so that they, too, will fit in smaller containers. We seldom need the full length of a resistor lead—and on the rare occasions when it’s useful, an additional piece of insulated wire can be added to the breadboard instead.Figure 16 shows one option for storing the 30 most commonly used values. Like the storage system for capacitors, this one won’t spill any components if you knock it over. Each compartment can hold at least 50 resistors (see Figure 17).
Figure 16. Slightly larger jewelry storage containers are good for resistors, if the leads are trimmed.
Figure 17. Fifty resistors can be stored in one of these little containers.
When I’m building a circuit, I try to discipline myself to check the value of each resistor or capacitor before I place it on the breadboard. A 10µF ceramic capacitor looks almost identical to a 0.1µF ceramic capacitor, and resistor values such as 1K and 1M are only one colored band apart. If component values become mixed up, you will find yourself faced with faults that can be truly perplexing.
To simplify the checking process for resistors, I use a mini-breadboard with jumper wires clipped to the probes of an auto-ranging meter, as shown in Figure 18. All I have to do is push the leads of a resistor into the board, and verification takes about five seconds. The breadboard sockets add a small amount of resistance, but only a few ohms, and I’m usually not concerned with a precise value, anyway. I just want to be sure that I’m not making a significant error. For the same reason, the cheapest possible meter can be used for this task.
Figure 18. A simple system for quickly verifying resistor values before using them in a project.
So much for the introductory material. Now let’s make more electronics!