Tools and Supplies for Laser Experimentation

Take a long look at the tools in your garage or workshop. You probably have all the implements necessary to build your own laser systems. Unless your designs require a great deal of precision (and most don’t), a common assortment of hand tools are all that’s really required to construct all sorts of laser projects.

Most of the hardware, parts, and supplies are things you probably already have that are left over from old projects from around the house. The pieces you don’t have can be readily purchased at a hardware store and a few specialty stores around town or through the mail.

This section discusses the basic tools and supplies needed for constructing hobby laser systems and how you might use them. You should consider this section a guide only; suggestions for tools and supplies are just that—suggestions. By no means should you feel that you must own each tool mentioned in this section or have on hand all the parts and supplies.

Some supplies and parts might not be readily available to you, and it’s up to you to consider alternatives and how to work these alternatives into the design. Ultimately, it will be your task to take a trip to the hardware store, collect various miscellaneous items, and go home to hammer out a unique creation that’s all your own.

CONSTRUCTION TOOLS

Construction tools are the things you use to fashion the frame and other mechanical parts of the laser system. These include hammer, screwdriver, saw, and so forth. Tools for the assembly of the electronic subsystems are discussed later on.

Basic Tools

No workshop is complete without the following:

* Claw hammer, used for just about anything you can think of.

* Rubber mallet, for gently bashing pieces together that resist going together; also for forming sheet metal.

* Screwdriver assortment, including various sizes of flat-head and Philips-head screwdrivers. A few long-blade screwdrivers are handy to have, as well as a ratchet driver. Get a screwdriver magnetizer/demagnetizer to magnetize the blade so it attracts and holds screws for easier assembly.

* Hacksaw, to cut anything. The hacksaw is the staple of the laser hobbyist. Get an assortment of blades. Coarse-tooth blades are good for wood and PVC pipe plastic; fine-tooth blades are good for copper, aluminum, and light-gauge steel.

* Miter box, to cut straight lines. Buy a good miter box and attach it to your work table (avoid wood miter boxes; they don’t last). You’ll also use the box to cut stock at near-perfect 45-degree angles, helpful when building optical benches.

* Wrenches, all types. Adjustable wrenches are helpful additions to the shop but careless use can strip nuts. The same goes for long-nosed pliers, useful for getting at hard-to-reach places. A pair or two vise-grips (indispensable in my workshop) help you hold pieces for cutting and sanding. A set of nut-drivers make it easy to attach nuts to bolts.

* Measuring tape. A six- or eight-foot steel measuring tape is a good choice. Also get a cloth tape at a fabric store for measuring flexible things.

* Square, for making sure that pieces you cut and assemble from wood, plastic, and metal are square.

* File assortment, to smooth the rough edges of cut wood, metal, and plastic (particularly important when working with metal for safety).

* Drill motor. Get one that has a variable speed control (reversing is nice but not absolutely necessary). If the drill you have isn’t variable speed, buy a variable-speed control for it. You need to slow the drill when working with metal and plastic. A fast drill motor is good for wood only. The size of the chuck isn't important, because most of the drill bits you’ll be using will fit a standard ¼-inch chuck.

* Drill bit assortment. Good, sharp ones only. If yours are dull, have them sharpened (or do it yourself with a drill-bit sharpening device), or buy a new set. Never use dull drill bits or your laser systems won’t turn out.

* Vise, for holding parts while you work. A large vise isn’t required, but you should get one that’s big enough to handle the size of pieces you’ll be working with.

* Clear safety goggles. Wear them when hammering, cutting, drilling, and any other time flying debris could get in your eyes.

If you plan on building your laser systems from wood, you might want to consider adding rasps, wood files, coping saws, and other woodworking tools to your toolbox. Working with plastic requires a few extras as well, including a burnishing wheel to smooth the edges of the cut plastic (a flame from a cigarette lighter also works but is harder to control), a strip-heater for bending, and special plastic drill bits. These bits have a modified tip that isn’t as likely to rip through the plastic material. Bits for glass can be used as well. Small plastic parts can be cut and scored using a sharp razor knife or razor saw, available at hobby stores.

Optional Tools

There are a number of tools you can use to make your time in the laser shop more productive and less time-consuming. A drill press helps you drill better holes, because you have more control over the angle and depth of each hole. Use a drill press vise to hold the pieces; never use your hands.

A table saw or circular saw makes cutting through large pieces of wood and plastic easier. Use a guide fence, or fashion one out of wood and clamps, to ensure a straight cut. Be sure to use a fine-tooth saw blade if cutting through plastic. Using a saw de signed for general wood-cutting will cause the plastic to shatter.

A motorized hobby tool is much like a hand-held router. The bit spins very fast (25,000 rpm and up), and you can attach a variety of wood-, plastic-, and metal-working bits to it. The better hobby tools, such as those made by Dremel and Weller, have adjustable speed controls. Use the right bit for the job. E.g., don’t use a wood rasp bit with metal or plastic, because the flutes of the rasp will too easily fill with metal and plastic debris.

A nibbling tool is a fairly inexpensive accessory (under $40) that lets you “nibble” small chunks from metal and plastic pieces. The maximum thickness depends on the bite of the tool, but it’s generally about 1/16- or 1/8-inch. Use the tool to cut channels, enlarge holes, and so forth. A tap and die set lets you thread holes and shafts to accept standard size nuts and bolts. Buy a good set. A cheap assortment of taps and dies is more trouble than its worth.

A thread size gauge made of stainless steel might be expensive ($20 to $42), but it helps you determine the size of any standard SAE or metric bolt. It’s a great accessory for tapping and dieing. Most gauges can be used when chopping threads off bolts with a hacksaw, providing a cleaner cut.

A brazing tool or small welder lets you spot-weld two metal pieces together. These tools are designed for small pieces only; they don’t provide enough heat to adequately weld pieces larger than a few inches in size. Be sure that extra fuel and /or oxygen cylinders or pellets are readily available for the brazer or welder you buy. There’s nothing worse than spending $50 to $70 for a home welding set, only to discover that supplies are not available for it. Be sure to read the instructions that accompany the welder and observe all precautions.

A caliper and micrometer let you measure small things such as lenses and other optical components. The projects in this book don’t call for an extremely accurate caliper or micrometer, but if you’re serious about laser work you’ll want the best laboratory grade instruments you can afford. At the very least, the caliper should be accurate to ‘/64 of an inch and the micrometer to 0.001 of an inch.

ELECTROMC TOOLS

Constructing electronic circuit boards or wiring the power system of your laser requires only a few standard electronic tools. A soldering iron leads the list. For maximum flexibility, invest in a modular soldering pencil with a 25- to 30-watt heating element. Anything higher could damage electronic components. (If necessary, a 40- or 50-watt element can be used for wiring switches, relays, and power transistors.) Stay away from “instant-on” soldering irons. Supplement your soldering iron with these accessories:

* Soldering stand, for keeping the soldering pencil in a safe, upright position.

* Soldering tip assortment. Get one or two small tips for intricate PCB work and a few larger sizes for routine soldering chores.

* Solder. Resin- or flux-core only. Acid core and silver solder should never be used on electronic components.

* Sponge, for cleaning the soldering tip during use. Keep the sponge damp and wipe the tip clean after every few joints.

* Heatsink, for attaching to sensitive electronic components during soldering. The heatsink draws the excess heat away from the component to help prevent damage to it.

* De-soldering vacuum tool, to soak up molten solder. Used to get rid of excess solder, to remove components, or redo a wiring job.

* Soldering or “dental” picks, for scraping, cutting, forming, and gouging into the work.

* Resin cleaner. Apply the cleaner after soldering is complete to remove excess resin.

* Solder vise or “third hand.” The vise holds together pieces to be soldered, leaving you free to work the iron and feed the solder.

VOLT-OHMMETER

A volt-ohmmeter is used to test voltage levels and the impedance of circuits. This moderately priced electronic tool is the basic requirement for working with electronic circuits of any kind. If you don’t already own a volt-ohmmeter, seriously consider buying one. The cost is minimal considering the usefulness of the device.

There are many volt-ohmmeters (or VOMs) on the market today. For work on lasers, you don’t want a cheap model, but you don’t need an expensive one. A meter of intermediate quality is sufficient and does the job admirably. The price for such a meter is between $30 and $75. Meters are available at Radio Shack and most electronics outlets. Shop around and compare features and prices.

Digital or Analog

There are two general types of VOMs available today: digital and analog. The difference isn't that one meter is used on digital circuits and the other on analog circuits. Rather, digital meters employ a numeric display not unlike a digital clock or watch, and analog VOMs use the older fashioned—but still useful—mechanical movement with a needle that points to a set of graduated scales.

Digital VOMs used to cost a great deal more than the analog variety, but the price difference has evened out recently. Digital VOMs, such as the one shown in ill. 23-1, are fast becoming the standard; in fact, it’s becoming difficult to find a decent analog meter anymore.

ill. 23-1. A typical digital volt-ohmmeter.

Analog VOMs are traditionally harder to use, because you must select the type and range of voltage you are testing, find the proper scale on the meter face, then estimate the voltage as the needle swings into action. Digital VOMs, on the other hand, display the voltage in clear numerals and with a greater precision than most analog meters.

Automatic Ranging

As with analog meters, some digital meters require you to select the range before it can make an accurate measurement. E.g., if you are measuring the voltage of a 9-volt transistor battery, you set the range to the setting closest to, but above, 9 volts (with most meters it's the 20- or 50-volt range). Auto-ranging meters don’t require you to do this, so they are inherently easier to use. When you want to measure voltage, you set the meter to volts (either ac or dc) and take the measurement. The meter displays the results in the readout panel.

Accuracy

Little of the work you’ll do with laser circuits requires a meter that’s super accurate. A VOM with average accuracy is more than enough. The accuracy of a meter is the minimum amount of error that can occur when taking a specific measurement. E.g., the meter may be accurate to 2,000 volts, ± 0.8 percent. A 0.8-percent error at the kinds of voltages used in most laser experiments—typically 5 to 12 volts dc—is only 0.096 volts!

Digital meters have another kind of accuracy. The number of digits in the display determines the maximum resolution of the measurements. Most digital meters have 3 and one-half digits, so it can display a value as small as .001 (the half digit's a “1” on the left side of the display). Anything less than that isn't accurately represented.

Functions

Digital VOMs vary greatly in the number and type of functions they provide. At the very least, all standard VOMs let you measure ac volts, dc volts, milliamps, and ohms. Some also test capacitance and opens or shorts in discrete components like diodes and transistors. These additional functions are not absolutely necessary for building general-purpose laser circuits, but they are handy to have when troubleshooting a circuit that refuses to work.

The maximum ratings of the meter when measuring volts, milliamps, and resistance also varies. For most applications, the following maximum ratings are more than adequate:

dc Volts 1,000 volts

ac Volts 500 volts

dc Current 200 milliamps

Resistance 2 megohms

One exception to this is when testing current draw for motors and other high-demand circuits. All but the smallest dc motors draw an excess of 200 milliamps, and an entire laser system for a light show is likely to draw 2 or more amps. Obviously, this is far out of range of most digital meters. You might need to get a good assessment of current draw, especially if your laser projects are powered by batteries, but to do so, you’ll need either a meter with a higher dc current rating (digital or analog) or a special-purpose ac/dc current meter. You can also use a resistor in series with the motor and apply Ohm’s Law to calculate the current draw.

Meter Supplies

Meters come with a pair of test leads—one black and one red—each equipped with a needle-like metal probe. The quality of the test leads is usually minimal, so you might want to purchase a better set. The coiled kind are handy. They stretch out to several feet yet recoil to a manageable length when not in use.

• Standard leads are fine for most routine testing, but some measurements require the use of a clip lead. These attach to the end of the regular test leads and have a spring- loaded clip on the end. You can clip the lead in place so your hands are free to do other things. The clips are insulated to prevent short circuits.

Meter Safety and Use

Most applications of the meter involve testing low voltages and resistance, both of which are relatively harmless to humans. Sometimes, however, you might need to test high voltages—like the input to a power supply—and careless use of the meter can cause serious bodily harm. Even when you’re not actively testing a high-voltage circuit, dangerous currents might still be exposed.

Proper procedure for meter use involves setting the meter beside the unit under test, making sure it's close enough so that the leads reach the circuit. Plug in the leads and test the meter operation by first selecting the resistance function setting (use the smallest scale if the meter isn't auto-ranging). Touch the leads together: the meter should read 0 ohms.

If the meter does not respond, check the leads and internal battery and try again. If the display does not read 0 ohms, double-check the range and function settings and adjust the meter to read 0 ohms (not all digital meters have a 0 adjust, but most analog meters do).

Once the meter has checked out, select the desired function and range and apply the leads to the circuit under test. Usually, the black lead is connected to ground, and the red lead is connected to the various test points in the circuit.

When testing high-voltage circuits, make it a habit to place one hand in a pants pocket. With one hand out of the way, you are less likely to accidentally touch a live circuit.

LOGIC PROBE

Meters are typically used for measuring analog signals. Logic probes test for the presence or absence of low-voltage dc signals that represent digital data. The 0s and 1s are usually electrically defined as 0 and 5 volts, respectively, with TTL ICs. In practice, the actual voltages of the 0 and 1 bits depend entirely on the circuit. You can use a meter to test a logic circuit, but the results aren’t always predictable. Further, many logic circuits change states (pulse) quickly and meters cannot track the voltage switches fast enough.

Logic probes, such as the model in ill. 23-2, are designed to give a visual and (usually) aural signal of the logic state of a particular circuit line. One LED on the probe lights up if the logic is 0 (or Low), another LED lights up if the logic is 1 (or HIGH). Most probes have a built-in buzzer that has a different tone for the two logic levels. That way, you don’t need to keep glancing at the probe to see the logic level.

ill. 23-2. A logic probe.

A third LED or tone can indicate a pulsing signal. A good logic probe can detect that a circuit line is pulsing at speeds of up to 10 MHz, which is more than fast enough for laser applications, even when using computer control. The minimum detectable pulse width (the time the pulse remains at one level) is 50 nanoseconds, again more than sufficient.

Although logic probes might sound complex, they are really simple devices and their cost reflects this. You can buy a reasonably good logic probe for under $40. Most probes are not battery operated; rather, they obtain operating voltage from the circuit under test. You can also make a logic probe if you wish. A number of project books provide plans.

Using a Logic Probe

The same safety precautions apply when using a logic probe as they do when using a meter. Be wary when working close to high voltages. Cover them to prevent accidental shock (for obvious reasons, logic probes are not meant for anything but digital circuits, so never apply the leads of the probe to an ac line). Logic probes cannot operate with voltages exceeding about 15 volts dc, so if you are unsure of the voltage level of a particular circuit, test it with a meter first.

Successful use of the logic probe really requires you to have a circuit schematic to refer to. Keep it handy when troubleshooting your projects. It’s nearly impossible to blindly use the logic probe on a circuit without knowing what you are testing. And because the probe receives its power from the circuit under test, you need to know where to pick off suitable power. To use the probe, connect the probe’s power leads to a voltage source on the board, clip the black ground wire to circuit ground, and touch the tip of the probe against a pin of an integrated circuit or the lead of some other component. For more information on using your probe, consult the manufacturer’s instruction sheet.

LOGIC PULSER

A handy troubleshooting accessory when working with digital circuits is the logic pulser. This device puts out a timed pulse, letting you see the effect of the pulse on a digital circuit. Normally, you’d use the pulser with a logic probe or an oscilloscope (discussed below). The pulser is switchable between one pulse and continuous pulsing. You can make your own pulser out of a 555 timer IC. Ill. 23-3 shows a schematic you can use to build your own 555-based pulser; TABLE 23-1 provides a parts list.

Most pulsers obtain their power from the circuit under test. It’s important that you remember this. With digital circuits, it’s generally a bad idea to present to a device an input signal that's greater than the supply voltage for the device. In other words, if a chip is powered by 5 volts, and you give it a 12-volt pulse, you’ll probably ruin the chip. Some circuits work with split (+, —, and ground) power supplies (especially circuits with op amps and digital-to-analog converters). Be sure to connect the leads of the pulser to the correct power points.

ill. 23-3. Schematic diagram for making your own logic pulser. With the components shown, output frequency is approximately 2.5 Hz to 33 Hz.

Also be sure that you don't pulse a line that has an output but no input. Some integrated circuits are sensitive to unloaded pulses at their output stages, and improper application of the pulse can destroy the chip.

OSCILLOSCOPE

An oscilloscope is a pricey tool—good ones start at about $500—and only a small number of electronic and laser hobbyists own one. For really serious work, however, an oscilloscope is an invaluable tool—one that will save you hours of time and frustration.

Things you can do with a scope include some of the things you can do with other test equipment, but oscilloscopes do it all in one box and generally with greater precision. Among the many applications of an oscilloscope, you can:

* Test dc or ac voltage levels.

* Analyze the waveforms of digital and analog circuits.

* Determine the operating frequency of digital, analog, and RF circuits.

* Test logic levels.

* Visually check the timing of a circuit to see if things are happening in the correct order and at the prescribed time intervals.

Table 23-1. Logic Pulser Parts List

• C2 0.1 uF
• IC1 LM555 timer IC
• R1 250 k-ohm potentiometer
• R2 10 k-ohm resistor
• C1 2.2 uF electrolytic capacitor
• C2 0.1 uF disc capacitor

The designs provided in this book don’t absolutely require the use of an oscilloscope, but you’ll probably want one if you design your own circuits or want to develop your electronic skills. A basic, no-nonsense model is enough, but don’t settle for the cheap, single-trace units. A dual-trace (two channel) scope with a 20 to 25 MHz maximum input frequency should do the job nicely. The two channels let you monitor two lines at once, so you can easily compare the input signal and output signal at the same time. You don't need a scope with storage or delayed sweep, although if your model has these features, you’re sure to find a use for them sooner or later.

Scopes are not particularly easy to use; they have lots of dials and controls that set operation. Thoroughly familiarize yourself with the operation of your oscilloscope before using it for any construction project or for troubleshooting. Knowing how to set the time- per-division knob is as important as knowing how to turn the scope on. As usual, exercise caution when using the scope with or near high voltages.

Lastly, don’t rely on just the instruction manual that came with the set to learn how to use your new oscilloscope. Buy (and read!) a good book on how to effectively use your scope. Here is our dedicated web site on using oscilloscopes.

FREQUENCY METER

A frequency meter (or frequency counter) tests the operating frequency of a circuit. Most models can be used on digital, analog, and RF circuits for a variety of testing chores—from making sure the crystal analog-to-digital circuit's working properly to determining the modulation frequency of your laser beam communication system. You need only a basic frequency meter—a $200 or so investment. Or you can save some money by building a frequency meter kit.

Frequency meters have an upward operating limit, but it’s generally well within the region valid to laser experiments. A frequency meter with a maximum range of up to 50 MHz is enough. A couple of meters are available with an optional pre-scaler, a device that extends the useful operating frequency to well over 100 MHz.

WIRE-WRAPPING TOOL

Making a printed-circuit board for a one-shot application is time consuming, though it can be done with the proper kits and supplies. Conventional point-to-point solder wiring isn't an acceptable approach when constructing digital and high-gain analog circuits, which represent the lion’s share of electronics you’ll be building for your lasers.

The preferred construction method is wire-wrapping. Wire-wrapping is a point-to- point wiring system that uses a special tool and extra-fine 28- or 30-gauge wrapping wire. When done properly, wire-wrapped circuits are as sturdy as soldered circuits, and you have the added benefit of making modifications and corrections without the hassle of desoldering and resoldering.

A manual wire-wrapping tool is shown in ill. 23-4. You insert one end of the stripped wire into a slot in the tool, and place the tool over a square-shaped wrapping post. Give the tool five to ten twirls, and the connection is complete. The edges of the post keep the wire anchored in place. To remove the wire, use the other end of the tool and undo the wrapping.

Wrapping wire comes in many forms, lengths, and colors, and you need to use special wire-wrapping sockets and posts. See the section below on electronic supplies and components for more details.

BREADBOARD

You should test each of the circuits you want to use with your lasers (including the ones in this book) on a solderless breadboard before you commit it to wire-wrap or sol der. Breadboards consist of a series of holes with internal contacts spaced 1/10 of an inch apart, which is the most common spacing for ICs. You plug in ICs, resistors, capacitors, transistors, and 20- or 22-gauge wire in the proper contact holes to create your circuit.

Solderless breadboards come in many sizes. For the most flexibility, get a double- width board, one that can accommodate at least 10 ICs. Smaller boards can be used for simple projects; circuits with a high number of components require bigger boards. While you’re buying a breadboard, purchase a set of pre-colored wires. The wires come in a variety of lengths and are already stripped and bent for use in breadboards. The set costs $10 to $17, but the price is well worth the time you’ll save.

HARDWARE SUPPLIES

ill. 23-4. A wire-wrapping tool in action

A fully functional laser system of just about any description is about 75 percent hardware and 25 percent electronic and electromechanical. Most of your trips to get parts for your laser schemes will be to the local hardware store. Here are some common items you’ll want to have around your shop:

Nuts and Bolts

Number 8 and 10 nuts and pan-head stove bolts (8/32 and 10/24, respectively) are good for all-around construction. Get a variety of bolts in 1/2-, ¾-, 1-, 1¼, and 1½-inch lengths. You may also want to get some 2-inch and 3-inch-long bolts for special applications.

Motor shafts and other heavy-duty applications require ¼-inch 20 or /16-inch hardware. Pan-head stove bolts are the best choice; you don’t need hex-head carriage bolts unless you have a specific requirement for them. You can use number 6 (6/32) nuts and bolts for small, lightweight applications.

Washers

While you’re at the store, stock up on flat washers, fender washers (large washers with small holes), tooth lockwashers and split lockwashers. Get an assortment for the various sizes of nuts and bolts. Split lockwashers are good for heavy-duty applications because they provide more compression locking power. You usually use them with bolt sizes of ¼-inch and larger.

All-Thread Rod

All-thread is 2- to 3-foot lengths of threaded rod stock. It comes in standard thread sizes and pitches. All-thread is good for shafts and linear motion actuators. Get one of each in 8/32, 10/24, and ¼-inch 20 threads to start.

Special Nuts

Coupling nuts are just like regular nuts but have been stretched out. They are de signed to couple two bolts or pieces of all-thread together, end to end. In lasers, you might use them for a variety of tasks including linear motion actuators and positioning tables.

Locking nuts have a piece of nylon built into them that provides a locking bite when threaded onto a bolt. Locking nuts are preferred over using two nuts tightened together.

EXTRUDED ALUMINUM

For most of your laser designs, you can take advantage of a rather common hardware item: extruded aluminum stock. This aluminum is designed for such things as building bathtub enclosures, picture frames, and other handyman applications and comes in various sizes, thicknesses, and configurations. Length is usually 6, 8, 10, or 12 feet, but if you needless, most hardware stores will cut to order (you save when you buy it in full lengths). The stock is available in plain (dull silver) anodized aluminum and gold anodized aluminum. Get the plain stuff—it’s 10 to 25 percent cheaper.

Two particularly handy stocks are 41/64-by-1/2-inch channel and 57/64-by- 9/16-by-1/16-inch channel (some stores sell similar stuff with slightly different dimensions). I use these extensively to make parts for optical benches, lens holders, and other laser system parts. Angle stock measuring 1-by-1-by- 1/6-inches is another frequently used item, usually employed for attaching cross bars and other structural components. No matter what size you eventually settle on for your own designs, keep several feet of the stuff handy at all times. You’ll use it often.

If extruded aluminum isn't available, another approach is to use shelving standards— the bar-like channel stock used for wall shelving. It’s most often available in steel, but some hardware stores carry it in aluminum (silver, gold, and black anodized).

The biggest problem with using shelving standards is that the slots can cause problems when drilling holes for hardware. The drill bits can slip into the slots, causing the hole to be off-center. Some standards have an extra lip on the inside of the channel that can interfere with some of the hardware you use to join the pieces together.

ANGLE BRACKETS

You need a good assortment of 3/8-inch and ½-inch galvanized iron brackets to join the extruded stock or shelving standards together. Use 1½-by-3/8-inch flat corner irons when joining pieces cut at 45-degree angles to make a frame. The 1-by-3/8-inch and 1½- by-1 1/2-by-3/8-inch corner angle irons are helpful when attaching the stock to base-plates and when securing various components.

ELECTROMC SUPPLIES AND COMPONENTS

Most of the electronic projects in this book and other books with digital and analog circuits depend on a regular stable of common electronic components. If you do any amount of electronic circuit building, you’ll want to stock up on the following standard components. Keeping spares handy prevents you from making repeat trips to the electronics store.

Resistors

Get a good assortment of ¼- or ½-watt resistors. Make sure the assortment includes a variety of common values and that there are several of each value. Supplement the assortment with individual purchases of the following resistor values: 270 ohm, 330 ohm, 1 k-ohm, 3.3 k-ohm, 10 k-ohm, and 100 k-ohm.

The 270 and 330 ohm values are often used with light-emitting diodes (LEDs) and the remaining values are common to TTL and CMOS digital circuits.

Variable Resistors

Variable resistors, or potentiometers (pots), are relatively cheap and are a boon when designing and troubleshooting circuits. Buy an assortment of the small PC-mount pots (about 80 cents each retail) in the 2.5k, 5k, 10k, 50k, 100k, 25 k-ohm and 1 megohm values. You’ll find 1 megohm pots often used in op amp circuits, so buy a couple extra of these. I also like to have several extra 10k and 100k pots around because these find heavy use in most all types of circuits.

Capacitors

Like resistors, you’ll find yourself returning to the same standard capacitor values project after project. For a well-stocked shop, get a dozen or so each of the following inexpensive ceramic disc capacitors: 0.1, 0.01, and 0.001 F. The 0.1 and 0.01 pF caps are used extensively as bypass components and are absolutely essential when building circuits with TTL ICs. You can never have enough of these.

Many circuits use the in-between values of 0.47, 0.047, and 0.022 uF so you may want to get a couple of these, too. Power supply, timing, and audio circuits often use larger polarized electrolytic or tantalum capacitors. Buy a few each of 1.0, 2.2, 4.7, 10 and 100 uF values. Some projects call for other values (in the pico-farad range and the 1000’s of microfarad range). You can buy these as needed unless you find yourself returning to standard values repeatedly.

Transistors

There are thousands of transistors available, and each one has slightly different characteristics than the others. However, most applications need nothing more than “generic” transistors for simple switching and amplifying. Common npn signal transistors are the 2N2222 and the 2N3904. Both kinds are available in bulk packages of 10 for about $2. Common pnp signal transistors are the 2N3906 and the 2N2907. Price is the same or a little higher.

I don’t discriminate between the plastic and metal can transistors. E.g., technically speaking, the plastic 2N2222 are called PN2222 while the metal can version carries the 2N2222 designator. In any case, buy the plastic ones because they’re cheaper.

If the circuit you’re building specifies another transistor than the generic kind, you might still be able to use one of these if you first look up the specifications of the transistor called for in the schematic. A number of cross-reference guides provide the specifications and replacement-equivalents for popular transistors.

There are common power transistors as well. The npn TIP31 and TIP41 are familiar to most anyone who has dealt with power switching or amplification of up to 1 amp or so. The pnp counterparts are the T1P32 and T1P42. These transistors come in the TO-220 style package.

A common larger capacity npn transistor that can switch 10 amps or more is the 2N3055. It comes in the TO-3 style package and is available everywhere. Price is between 50 cents and $2, depending on the source.

Diodes

Common diodes are the 1N914 for light-duty signal switching applications and the 1N4000 series (1N4001, 1N4002, and so forth). Get several of each and use the proper size to handle the current in the circuit. Refer to a data-book on the voltage and power handling capabilities of these diodes.

LEDs

All semiconductors emit light (either visible or infrared), but light-emitting diodes (LEDs) are especially designed for the task. LEDs last longer than regular filament lamps and require less operating current. They are available in a variety of sizes, shapes, and colors. For general applications, the medium-sized red LED is perfect. Buy a few dozen and use them as needed. Some of the projects in this book call for infrared LEDs. These emit no visible light and are used in conjunction with an infrared-sensitive phototransistor or photodiode.

The project in Section 4, “Experimenting With Light and Optics,” uses a special high-power visible red LED. Refer to that section for more information on this LED and where to obtain it.

Integrated Circuits

Integrated circuits let you construct fairly complex circuits from just a couple of components. Although there are literally thousands of different ICs, some with exotic applications, a small handful crops up again and again in hobby projects. You should keep the following ICs in ready stock:

* 555 timer. This is by far the most popular integrated circuit for hobby electronics. With just a couple of resistors and capacitors, the NE555 can be made to act as a pulser, a timer, a time delay, a missing pulse detector, and dozens of other useful things. The chip is usually used as a pulse source for digital circuits. It’s available in dual versions as the 556 and quadruple versions as the 558. A special CMOS version lets you increase the pulsing rate to 2 MHz.

* LM741 op amp. The LM741 comes second in popularity to the 555. The 741 can be used for signal amplification, differentiation, integration, sample-and-hold, and a host of other useful applications. The 741 is available in a dual version—the 1458. The chip comes in different package configurations. The schematics in this book and those usually found elsewhere, specify the pins for the common 8-pin DIP package. If you are using the 14-pin DIP package or the round can package, check the manufacturer’s data sheet for the correct pinouts. Note that there are numerous op amps available, and some have design advantages over the 741.

* TTL chips. TTL ICs are common in computer circuits and other digital applications. There are many types of TTL packages, but you won’t use more than 10 or 15 of them unless you’re heavily into electronics experimentation. Specifically, the most common and most useful T’FL ICs are the 7400, 7401, 7402, 7404, 7407, 7408, 7414, 7430, 7432, 7473, 7474, 74154, 74193, and 74244. All or many of these are available in “T’FL chip assortments” through some of the mail-order electronics firms.

* CMOS chips. Because CMOS ICs require less power to operate than the TTL variety, you’ll often find them specified for use with low-power laser and remote-control applications. Like TTL, there is a relatively small number of common packages: 4001, 4011, 4013, 4016, 4017, 4027, 4040, 4041, 4049, 4060, 4066, 4069, 4071, and 4081.

Wire

Solid-conductor, insulated, 22-gauge hookup wire can be used in your finished projects as well as connecting wires in breadboards. Buy a few spools in different colors. Solid- conductor wire can be crimped sharply and can break when excessively twisted and flexed. If you expect that wiring in your project might be flexed repeatedly, use stranded wire instead. Heavier 12- to 18-gauge hookup wire is required for connection to heavy-duty batteries, motors, and circuit-board power supply lines.

Wire-wrap wire is available in spool or pre-cut/pre-stripped packages. For ease of use, buy the more expensive pre-cut stuff unless you have a tool that does it for you. Get several of each length. The wire-wrapping tool has its own stripper built in (which you must use instead of a regular wire stripper), so you can always shorten the precut wires as needed. Some special wire-wrapping tools require their own wrapping wire. Check the instruction that came with the tool for details.

CIRCUIT BOARDS

Simple projects can be built onto solder breadboards. These are modeled after the solderless breadboard, so you simply transfer the tested circuit from the solderless breadboard to the solder board. You can cut the board with a hacksaw or razor saw if you don’t need all of it.

Larger projects require perforated boards. Get the kind with solder tabs or solder traces on them. You’ll be able to secure the components onto the boards with solder. Most pen boards are designed for wire-wrapping.

IC Sockets

You should use sockets for ICs whenever possible. Sockets come in sizes ranging from 8-pin to 40-pin. The sockets with extra-long square leads are for wire-wrapping.

You can also use wire-wrap IC sockets to hold discrete components like resistors, capacitors, diodes, LEDs, and transistors. You can, if you wish, wire-wrap the leads of these components, but because the leads are not square, the small wire doesn’t have anything to bite into, so the connection won’t be very strong. After assembly and testing and you are sure the circuit works, apply a dab of solder to the leads to hold the wires in place.

SETTING UP SHOP

You’ll need a work table to construct the mechanisms and electronic circuits of your lasers and laser systems. Electronic assembly can be indoors or out, but I’ve found that when working in a carpeted room, it’s best to spread another carpet or some protective cover over the floor. When the throw rug fills with solder bits and little pieces of wire and component leads, I can take it outside, beat it with a broom handle, and it’s as good as new.

Unlike the manufacturing process, actual use of your laser system should be done indoors, in a controlled environment. You’ll be using precision optics, so you should avoid exposing them to dust, dirt, and temperature extremes often found in garages. If you plan on building a sand box holography system as described in Sections 17 and 18, you must be sure to keep the table indoors and away from moisture, because sand has a tendency to soak up water that can impede the creation of your holographic masterpieces.

Whatever space you choose for your laser lab, make sure all your tools are within easy reach. Keep special tools and supplies in an inexpensive fishing tackle box. Tackle boxes have lots of small compartments for placing screws and other parts.

For best results, your workspace should be an area where the laser system in progress won't be disturbed if you have to leave it for several hours or days (as will usually be the case). The work table should also be one that's off limits or inaccessible to young children or at least an area that can be easily supervised. This is especially true of helium neon-based lasers and the high-voltage power supplies used with them.

Good lighting is a must. Both mechanical and electronic assembly require detail work, and you need good lighting to see everything properly. Supplement overhead lights with a 60-watt desk lamp. You’ll be crouched over the worktable for hours at a time, so a comfortable chair or stool is a must, and be sure the seat is adjusted for the height of the worktable.