CHAPTER 6

TOOLS
Take a look at the tools in your garage or workshop. You probably already have all the implements required to build your own robot. Unless your robot designs require a great deal of precision (and most hobby robots don’t), a common assortment of hand tools is all that’s really needed to construct robot bodies, arms, drive systems, and more. Most of the hardware, parts, and supplies you need are also things you probably already have, left over from old projects around the house. You can readily purchase the pieces you don’t have at a hardware store, a few specialty stores around town, or through the mail.
This chapter discusses the basic tools for hobby robot building and how you might use them. You should consider this chapter only as a guide; suggestions for tools are just that— suggestions. By no means should you feel that you must own each tool or have on hand all the parts and supplies mentioned in this chapter. You may have tools that you like to use that aren’t listed in this chapter. Once again, the concept behind this book is to provide you with the know-how to build robots from discrete modules. In keeping with that open-ended design, you are free to exchange parts in the modules as you see fit. Some supplies and parts may not be readily available to you, so it’s up to you to consider alternatives and how to work them into your design. Ultimately, it will be your task to take a trip to the hardware store, collect the items you need, and hammer out a unique creation that’s all your own.
6.1 Safety
When building a robot, there should be one overriding concern and that is the safety of you and the other people building the robot. A momentary distraction or a few seconds of carelessness can lead to you or somebody else being seriously hurt. There are a few simple rules to follow when building robots to make sure that everyone is safe and, even if accidents happen, to minimize the chances for injuries.
1.  Always wear safety glasses. There are a variety of different safety glasses available. Make sure you get ones that have shatterproof glass and side protection. If you wear glasses, use safety glasses that fit over your regular glasses or have a pair made with impact-resistant lenses and side shields.
2.  Never disable or take off tool safety devices. This apparatus may seem to make the work more difficult and harder to observe, but they are there for a purpose. If doing the work seems to be particularly onerous due to the safety devices, then chances are you are not using the tool correctly.
3.  Always work in a well-ventilated area. Some tools or building processes output gases that are not normally toxic, but in a closed environment can be dangerous. If you are working in a garage, it is a good idea to install a bathroom exhaust fan.
4.  Never work without somebody nearby. There will be times when you work on your own, but make sure there is somebody you can call out to if there is a problem—never work alone in a house.
5.  If something goes wrong, take a few minutes to figure out what was its root cause and how to either fix it or prevent it from happening again later. Try to avoid getting frustrated or angry at the work and instead go back and fix the reasons for the problem.
6.  Practical jokes have no place in a workshop. Things that seem funny at the spur of the moment can unleash a catastrophic chain of events.
7.  Keep a fire extinguisher in the work area. Cutting tools can throw off sparks or raise the temperature of materials to the flashpoint of wood and paper. Soldering irons, by definition, are very hot. Short-circuited batteries can become extremely hot and their casings catch fire.
8.  Make sure there is a telephone close by. Ideally “911” should be programmed into it.
The most important rule is to never use a tool unless you are trained in its operation and understand all the safety issues. The same goes for chemicals; even apparently benign compounds can become dangerous with the right set of circumstances. Make sure you read and are familiar with all manuals, material safety sheets, and any plan notes before starting work.
Following these simple rules and properly preparing to do the work will greatly minimize the chances of somebody getting hurt.
6.2 Setting Up Shop
You’ll need a worktable to construct the mechanisms and electronic circuits of your robots. The garage is an ideal location because it affords you the freedom to cut and drill wood, metal, and plastic without worrying about getting pieces in the carpet or tracking filings and sanding dust throughout the house. The garage is also good because it will minimize any trapped paint or chemical smells, and on those occasions when you burn out an electrical or electronic device, the house won’t take on the smell of a store having a fire sale. Your new hobby will be better tolerated and even encouraged if it does not result in extra work or inconvenience for anyone you live with.
In whatever space you choose to set up your robot lab, make sure all your tools are within easy reach. You can keep special tools and supplies in an inexpensive fishing tackle box. It provides lots of small compartments for screws and other parts. For best results, your work space should be an area where the robot-in-progress will not be disturbed if you have to leave it for several hours or several days, as will usually be the case. It should go without saying that the worktable and any power tools should also be off limits or inaccessible to young children.
Good lighting is a must. Both mechanical and electronic assembly requires detail work, and you will need good lighting to see everything properly. Supplement overhead lights with a 60-W desk lamp. You’ll be crouched over the worktable for hours at a time, so a comfortable chair or stool is a must. Be sure you adjust the seat for the height of the worktable.
It’s not a bad idea to set up your workshop with a networked PC and a phone to be electronically connected to the outside world as well as the systems within your house. Being able to talk to other people (either by phone or the Internet) will be useful, especially if you are having a problem and have the material and tools right in front of you. A PC networked to other PCs in the house could be used for displaying design drawings produced on another computer or allowing you to perform a quick web search for information. Remember to protect the PC and phone from dust and filings that could become airborne when material is being cut.
6.3 Basic Tools
Construction tools are what you use to fashion the frame and other mechanical parts (or structure) of the robot. We will look at the tools needed to assemble the electronics later in this chapter.
The basic tools for creating a robot include:
  • Claw hammer. These can be used for just about any purpose.
  • Rubber mallet. For gently bashing together pieces that resist being joined, nothing beats a rubber mallet; it is also useful for forming sheet metal.
  • Measurement tools. You should have a variety of metal scales, wood and plastic rulers all of varying lengths, as well as a cheap analog dial or digital calipers. You may also want to keep a drill diameter gauge handy along with tools for measuring screw diameters and pitches. Finally, kitchen and fishing scales are useful tools for keeping track of how much the robot is going to weigh.
  • Screwdriver assortment. Have several sizes of flat-head and Phillips-head screwdrivers. It’s also handy to have a few long-blade screwdrivers, as well as a ratchet driver. Get a screwdriver magnetizer/demagnetizer; it lets you magnetize the blade so it attracts and holds screws for easier assembly. Hacksaw. To cut anything, the hacksaw is the staple of the robot builder. Buy 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.
  • Hacksaw. To cut anything, the hacksaw is the staple of the robot builder. Buy 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 worktable (avoid wood miter boxes; they don’t last). You’ll also use the box to cut stock at near-perfect 45° angles, which is helpful when building robot frames.
  • Wrenches, all types. Adjustable wrenches are helpful additions to the shop but careless use can strip nuts. The same goes for long-nosed pliers, which are useful for getting at hard-to-reach places. One or two pairs of Vise-Grips will help you hold pieces for cutting and sanding. A set of nut drivers will make it easy to attach nuts to bolts.
  • Measuring tape. A 6- or 8-ft steel measuring tape is a good length to choose. Also get a cloth measuring tape at a fabric store so you can measure things like chain and cable lengths.
  • Square. You’ll need one to make sure that pieces you cut and assemble from wood, plastic, and metal are square.
  • File assortment. Files will enable you to smooth the rough edges of cut wood, metal, and plastic (particularly important when you are working with metal because the sharp, unfinished edges can cut you).
  • Motor drill. 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 is not important since most of the drill bits you’ll be using will fit a standard -in chuck.
  • Drill bit assortment. Use 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.
  • Vise. A vise is essential for holding parts while you drill, nail, and otherwise torment them. An extra large vise isn’t required, but you should get one that’s big enough to handle the size of the pieces you’ll be working with. A rule of thumb: a vice that can’t close around a 2-in block of metal or wood is too small.
  • Safety goggles. Wear them when hammering, cutting, and drilling as well as any other time when flying debris could get in your eyes. Be sure you use the goggles. A shred of aluminum sprayed from a drill bit while drilling a hole can rip through your eye, permanently blinding you. No robot project is worth that.
If you plan to build your robots from wood, you may want to consider adding rasps, wood files, coping saws, and other woodworking tools to your toolbox. Working with plastic requires a few extra tools as well, including a burnishing wheel to smooth the edges of the cut plastic (the 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. Small plastic parts can be cut and scored using a sharp razor knife or razor saw, both of which are available at hobby stores.
6.3.1 OPTIONAL TOOLS
There are a number of other tools you can use to make your time in the robot shop more productive and less time consuming. Note that many of these tools are powerful and cause a lot of injury or damage if you are not careful or are inexperienced in their use. If you are unfamiliar with any of the tools, do not buy or use them until you have received training in them!
images
Figure 6-1   A motorized hobby tool is ideal for drilling, sanding, and shaping small parts.
6.4 Electronic Tools
Constructing electronic circuit boards or wiring the power system of your robot requires only a few standard tools. A soldering iron leads the list. For maximum flexibility, invest in a modular soldering pencil, the kind that lets you change the heating element. For routine electronic work, you should get a 25- to 30-W heating element. Anything higher may damage electronic components. You can use a 40- or 50-W element for wiring switches, relays, and power transistors. Stay away from instant-on soldering irons. For any application other than soldering large-gauge wires they put out far too much heat.
As obvious as it seems to most people, do not use soldering iron, solder, or flux that is designed for plumbing applications. These tools and materials are not appropriate for any robot applications and could potentially damage the components being connected together.
  • Soldering stand. Mandatory for keeping the soldering pencil in a safe, upright position.
  • Soldering tip assortment. Get one or two small tips for intricate printed circuit board work and a few larger sizes for routine soldering chores.
  • Solder. Buy resin or flux core type that is designed for electronics. Acid core and silver solder should never be used on electronic components.
  • Solder sponge. Sponges are useful for cleaning the soldering tip as you use it. Keep the sponge damp, and wipe the tip clean every few joints.
  • Desoldering vacuum tool. This is useful for soaking up molten solder. Use it to get rid of excess solder, remove components, or redo a wiring job.
  • Solder braid. Performs a similar function to the desoldering vacuum tool by wicking excess molten solder away from a joint or a component.
  • Dental picks. These are ideal for probing and separating wires and component leads.
  • Resin cleaner. Apply the cleaner after soldering is complete to remove excess resin. An ultrasonic jewelry cleaner used with the resin cleaner (or isopropyl alcohol) will get the components very clean with very little work on your part.
  • Solder vise. This vise serves as a third hand, holding together pieces to be soldered so you are free to work the iron and feed the solder.
  • An illuminated magnifying glass. Often going by the trade name Dazer, this provides a two or three time magnification of the surface below. It is invaluable for inspecting work or soldering fine components.
6.4.1 STATIC CONTROL
Running robots are terrible environments for electronics. The motors tend to produce large transients on the power lines that come back to the control electronics, running across different surfaces will build up static electrical charges, and different metal parts can produce unexpected voltages and currents that can upset electronics. Fortunately, most modern electronic devices are protected from static electrical discharges, but you should still make some basic concessions to protect them from being damaged during assembly and operation.
Everybody is familiar with the sparks that you can produce by shuffling along a synthetic carpet and touching a metal doorknob. What will probably surprise you is the magnitude of the voltage needed to produce a spark: for you to feel and see the spark, a static charge of 2500 V or more is required. The minute amount of current flow (on the order of microamperes) is why you are not hurt. As you have probably heard, when somebody is electrocuted it is the current that kills, not the voltage.
The amount of static electricity that can damage a silicon chip is significantly less— 125 V can ruin a diode’s PN junction or a MOSFET’s gate oxide layer. Note that 125 V is 20 times less than the 2500-V threshold needed to detect static electricity. This relatively low level is the reason for the concern about static electricity. The term electrostatic discharge (ESD) is used to describe the release of static electricity (either from you to the doorknob or into an electronic circuit). Virtually all modern electric devices have built-in protections against ESD, but there are still a number of things that you must do to ensure that the components are not damaged by static electricity, either during assembly or use.
You can buy basic ESD protection kits, which consist of a conducting mat, a wrist strap with cord, and a static bleed line that can be attached to the grounding screw (holding the faceplate on an electrical outlet), for about $20. Before buying this type of kit, there are a number of things that you should be aware of. First, the term conducting when applied to the mat, the wrist strap, and the static bleed line is very loosely applied; each of these components should have internal resistances in the mega-ohm range. Do not buy an ESD kit that does not have a mega-ohm resistor in the wrist strap cord or the static bleed line as there could be dangerous voltages passed along them into you. Finally, before attaching the static bleed line to the electrical outlet’s grounding screw make sure that the socket is wired properly using a socket tester (which costs around $5).
All circuit assembly should take place on the conducting mat while you are wearing the wrist strap. When you buy electronic components, they will either be packaged in conducting plastic tubes or in anti-static bags. When you have completed the assembly operation, the components should be returned to their original packages and any assembled circuitry placed inside an anti-static bag. Operation of the circuitry can have potential problems as was noted at the start of this section. To minimize the chance of the robot’s electronics becoming damaged, there are a few precautions that can be taken:
  • The metal parts of the robot should all be connected together and connected to the ground (negative) connection of the robot’s electronics. This will prevent static electricity from building up within the robot.
  • Robot whiskers must be connected to the ground as they can generate static electricity when they run across an object.
  • Castor mountings should be attached to the robot’s ground connection to avoid buildups of static electricity.
  • You might want to let a small metal chain or wire braid run on the ground while the robot is moving to help dissipate static charges from the robot.
  • The robot electronics should be within some kind of metal box to protect them from static electricity when the robot is picked up.
  • Connectors to PCs (e.g., USB or RS-232) for programming or monitoring must have the outside shells connected to the robot’s metal frame and negative connection to make sure any static electricity buildup is not passed through either the robot’s or the PC’s electronics, damaging them.
6.4.2 DIGITAL MULTIMETER
A digital multimeter (DMM and also known as a volt-ohm meter or multitester) is used to test voltage and current levels along with the resistance of different parts of circuits. Along with these basic functions, you can find DMMs that can test transistors and capacitors, and measure signal frequencies and temperature. They can be purchased from under $10 to several thousand, and if you don’t already own a volt-ohm meter you should seriously consider buying one immediately. The low cost of a simple unit is disproportionate to the usefulness of the instrument.
There are many DMMs on the market today. For robotics work, a meter of intermediate quality is sufficient and does the job admirably at a price between $30 and $75 (it tends to be on the low side of this range). Meters are available at Radio Shack and most electronics outlets.
While analog (meters with needles) multimeters are still available, you should avoid them. Digital meters employ a numeric display not unlike a digital clock or watch. Analog meters use the older-fashioned mechanical movement with a needle that points to a set of graduated scales. When they first became available, DMMs (like the one shown in Fig. 6-2) used to cost a great deal more than the analog variety, but now they generally cost less than analog meters, are more easily read, and are usually more robust. In fact, it’s hard to find a decent analog meter these days.
images
Figure 6-2   A volt-ohm meter (or multitester) checks resistance, voltage, and current. This model is digital and has a 3½-digit liquid crystal display (LCD) readout.
Most low-cost DMMs require you to select the range before it can make an accurate measurement. For example, if you are measuring the voltage of a 9-V transistor battery, you set the range to the setting closest to, but above, 9 V (with most meters it is the 0 to 20 or 0 to 50-V range). Auto-ranging meters (which cost more than the basic models) 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.
Little of the work you’ll do with robot circuits will require a DMM that’s superaccurate; when working with electronics, being within a few percentage points of the desired value is normally good enough for a circuit to work properly. The accuracy of a meter is the minimum amount of error that can occur when taking a specific measurement. For example, the meter may be accurate to 2000 V, plus or minus 0.8 percent. A 0.8 percent error at the kinds of voltages used in robots—typically, 5 to 12 V DC—is only 0.096 V.
The number of digits in the DMM display determines the maximum resolution of the measurements. Most DMMs have three and a half digits, so they can display a value as small as 0.001 (the half digit is a 1 on the left side of the display). Anything less than that is not accurately represented and there’s little need for accuracy better than this.
DMMs vary greatly in the number and type of functions they provide. At the very least, all standard meters 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 robot circuits, but they are handy when troubleshooting a circuit that refuses to work.
The maximum ratings of the meter when measuring volts, milliamps, and resistance also vary. Before buying a specific DMM, make sure you understand what the maximum values are that the meter can handle. Most DMMs have maximum values ratings in the ranges of:
 
DC voltages to 1000 V
AC voltages to 500 V
DC currents to 200 mA with up to 10 A using a fused input
Resistance 2 MΩ
 
One exception to this is when you are testing current draw for the entire robot versus just for motors. Many DC motors draw an excess of 200 mA, and the entire robot is likely to draw 2 or more amps. Obviously, this is far out of the range of most digital meters, but there are ways to do it as is shown in Chapter 19.
DMMs come with a pair of test leads, one black and one red. Each is equipped with a needlelike metal probe. Standard leads are fine for most routine testing, but some measurements may require that you use 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.
Most applications of the DMM involve testing low voltages and resistance, both of which are relatively harmless to humans. Sometimes, however, you may 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 can still be exposed.
The proper procedure for using a meter is to set it beside the unit under test, making sure it is close enough so 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 is not auto-ranging). Touch the leads together: the meter should read 0 Ω or something very close (a half ohm or so). If the meter does not respond, check the leads and internal battery and try again. Analog multimeters often have a “zero adjust,” which provides a basic calibration capability for the meter. 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 will be connected to the ground, and the red lead will be connected to the various test points in the circuit.
6.4.3 LOGIC PROBES
Meters are typically used for measuring analog signals. Logic probes test for the presence or absence of low-voltage digital data signals. The 0s and 1s are usually electrically defined as 0 and 5 V, respectively, when used with TTL integrated circuits (ICs). In practice, the actual voltages of the 0 and 1 bits depend entirely on the circuit and the parts used to make it up. 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 quickly enough.
Logic probes, such as the model in Fig. 6-3, are designed to give a visual and (usually) audible signal of the logic state of a particular circuit line. One LED (light-emitting diode) on the probe lights up if the logic is 0 (or low); another LED lights up if the logic is 1 (or high). You should only work with a probe that has a built-in buzzer with different tones for the two logic levels. This feature will allow you to look at the circuitry you are probing rather than having to glance at the probe to see the logic level.
images
Figure 6-3   The logic probe in use. Note that in the photograph the probe derives its power from the circuit under test.
A third LED or tone may 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 robotic applications, even when using computer control. The minimum detectable pulse width (the time the pulse remains at one level) is 50 nanoseconds, which again is more than sufficient.
Another feature that you should be aware of is the ability of the probe to work with different logic families and logic voltage levels. Different CMOS logic families can work at power supply voltages ranging from 3 to 15 V with a logic level transition voltage of one-half the power supply voltage (1.5 to 7.5 V). TTL logic’s transition voltage is usually regarded as 1.4 V and is independent of the input power supply (which ranges from 4.75 to 5.25 V). The logic technology that the probe works with is switch selectable.
Most probes are not battery operated; rather, they obtain operating voltage from the circuit under test. This feature allows you to start simply probing your circuit without providing a separate power supply (with a matching ground to the test circuit) for the logic probe and determining the appropriate CMOS logic test level.
Although logic probes may sound complex, they are really simple devices, and their cost reflects this. You can buy a reasonably good logic probe for under $20. The logic probe available from Radio Shack, which has most of the features listed here, can be purchased at this price point. You can also make a logic probe if you wish; it is not recommended as you will be hard pressed for buying the necessary parts for less than the cost of an inexpensive unit.
To use the logic probe successfully you really must 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 since 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 on an integrated circuit or the lead of some other component. For more information on using your probe, consult the manufacturer’s instruction sheet.
When designing your robot, it is a good idea to keep your digital logic separate from power supplies and other high-voltage/high-current circuits. When working on an awkward circuit, such as one mounted in a robot, it is not unusual for the metal probe tip to slip and short out other circuits. If the board is all digital logic, then this isn’t a problem—but if there are other circuits on the board, you could end up damaging them, your logic probe, and any number of miscellaneous circuits.
6.4.4 OSCILLOSCOPE
An oscilloscope is a pricey tool, but for performing serious work or understanding how the circuitry behaves in your robot, it is invaluable and will save you hours of frustration. Other test equipment will do some of the things you can do with a scope, but oscilloscopes do it all in one box and generally with greater precision. Among the many applications of an oscilloscope, you can do the following:
  • 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.
The most common application used to demonstrate the operation of an oscilloscope is converting sound waves into a visual display by passing the output of a microphone into an oscilloscope. This application, while very appealing, does not demonstrate any of the important features of an oscilloscope nor is it representative of the kind of signals that you will probe with it. When you are looking at buying an oscilloscope, you should consider the different features and functions listed in the following.
The resolution of the scope reveals its sensitivity and accuracy. On an oscilloscope, the X (horizontal) axis displays time, and the Y (vertical) axis displays voltage. These values can be measured by the marks, or graticules, on the oscilloscope display. To change the sensitivity, there is usually a knob on the oscilloscope that will make the time between each set of markings larger or smaller. The value between the graticule markings is either displayed on the screen itself electronically or marked on the oscilloscope by the adjustment knob (Fig. 6-4).
images
Figure 6-4   Digital storage oscilloscope display showing the changing voltage level on the two pins used in the BS2’s shiftout statement.
There are two different types of oscilloscopes. The analog oscilloscope passes the incoming signal directly from the input probes to the CRT display without any processing. Rather than displaying the signal as it comes in, there is normally a trigger circuit, which starts the display process when the input voltage reaches a specific point. Analog oscilloscopes are best suited for repeating waveforms; they can be used to measure their peak to peak voltages, periods, and timing differences relative to other signals.
The digital storage oscilloscope (DSO) converts the analog voltage to a digital value and then displays it on a computer-like screen. By converting the analog input to digital, the waveform can be saved and displayed after a specific event (also known as the trigger, as in the analog oscilloscope) or processed in some way. Whereas the peak to peak voltage and the waveform’s period is measured from the screen in an analog oscilloscope, most digital storage oscilloscopes have the ability to calculate these (and other) values for you. Digital storage oscilloscopes can be very small and flexible; there are a number of products available that connect directly to a PC and avoid the bulk and cost of a display all together. It should be noted that the digital storage oscilloscope is capable of displaying the same repeating waveforms as an analog oscilloscope.
One of the most important specifications of an oscilloscope is its bandwidth, which is the maximum frequency signal that can be observed accurately. For example, a 20 MHz oscilloscope can accurately display and measure a 20 MHz sine wave. The problem with most signals is that they are not perfect sine waves; they usually consist of much higher frequency harmonics, which make up the signal. To accurately display an arbitrary waveform at a specific frequency, the bandwidth must be significantly higher than the frequency itself; five times the required bandwidth is the minimum that you should settle for, with 10 times being a better value. So, if in your circuit, you have a 20 MHz clock, to accurately observe the signal the oscilloscope’s bandwidth should be 100 MHz or more.
Along with the bandwidth measurement in a digital storage oscilloscope, there is also the sampling rate of the incoming analog signal. The bandwidth measurement of a digital storage oscilloscope is still relevant; like the analog oscilloscope it specifies the maximum signal frequency that can be input without the internal electronics of the digital storage oscilloscope distorting it. The sampling rate is the number of times per second that the oscilloscope converts the analog signal to a digital value. Most digital storage oscilloscopes will sample at 10 to 50 times the bandwidth and the sampling measurement is in units of samples per second.
Finally, the oscilloscope’s trigger is an important feature that many people do not understand how to use properly. As previously noted, the trigger is set to a specific voltage to start displaying (or recording in the case of a digital storage oscilloscope) the incoming analog voltage signal. The trigger allows signals to be displayed without jitter so that the incoming waveform will be displayed as a steady waveform, instead of one that jumps back and forth or appears as a steady blur without any defined start point. The trigger on most oscilloscopes can start the oscilloscope when the signal goes from high to low at a specific voltage level, or from low to high.
Over the years, oscilloscopes have improved dramatically, with many added features and capabilities. Among the most useful features is a delayed sweep, which is helpful when you are analyzing a small portion of a long, complex signal. This feature is not something that you will be comfortable using initially, but as you gain experience with the oscilloscope and debugging you will find that it is an invaluable feature for finding specific problems or observing how the circuitry works after a specific trigger has been executed.
The probes used with oscilloscopes are not just wires with clips on the end of them. To be effective, the better scope probes use low-capacitance/low-resistance shielded wire and a capacitive-compensated tip. These ensure better accuracy.
Most scope probes are passive, meaning they employ a simple circuit of capacitors and resistors to compensate for the effects of capacitive and resistive loading. Many passive probes can be switched between 1X and 10X. At the 1X setting, the probe passes the signal without attenuation (weakening). At the 10X setting, the probe reduces the signal strength by 10 times. This allows you to test a signal that might otherwise overload the scope’s circuits.
Active probes use operational amplifiers or other powered circuitry to correct for the effects of capacitive and resistive loading as well as to vary the attenuation of the signal. Table 6-1 shows the typical specifications of passive and active oscilloscope probes.

TABLE 6-1   Specifications For Typical Oscilloscope Probe
table

As an alternative to a stand-alone oscilloscope you may wish to consider a PC-based oscilloscope solution. Such oscilloscopes not only cost less but may provide additional features, such as long-term data storage. A PC-based oscilloscope uses your computer and the software running on it as the active testing component.
Most PC-based oscilloscopes are comprised of an interface card or adapter. The adapter connects to your PC via an expansion board or a serial, parallel, or USB port (different models connect to the PC in different ways). A test probe then connects to the interface. Software running on your PC interprets the data coming through the interface and displays the results on the monitor. Some oscilloscope adapters are designed as probes with simple displays, giving you the capability of the DMM, logic probe, and oscilloscope in a package that you can hold in your hand.
Prices for low-end PC-based oscilloscopes start at about $100. The price goes up the more features and bandwidth you seek. For most robotics work, you don’t need the most fancy-dancy model. PC-based oscilloscopes that connect to the parallel, serial, or USB port—rather than internally through an expansion card—can be readily used with a portable computer. This allows you to take your oscilloscope anywhere you happen to be working on your robot.
The designs provided in this book don’t absolutely require that you use 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 analog units. A dual-trace (two-channel) digital storage oscilloscope with a 20- to 25-MHz maximum input frequency (with 250,000 samples per second) should do the job nicely. The two channels let you monitor two lines at once (and reference it to a third trigger line), so you can easily compare the input and output signals at the same time. The digital storage features will allow you to capture events and study them at your leisure, allowing you to track the execution progress of the software and its response to different inputs.
Oscilloscopes are not particularly easy to use for the beginner; they have lots of dials and controls for setting 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 oscilloscope on and you won’t be very efficient at finding problems until you understand exactly how the oscilloscopes trigger. As usual, exercise caution when using the scope with or near high voltages.
6.5 From Here
To learn more about . . .
  
Read
Electronic components
  
Chapter 5, “Electronic Components”
How to solder
  
Chapter 6, “Electronic Construction Techniques”
Building electronic circuits
  
Chapter 6, “Electronic Construction Techniques”
Building mechanical apparatuses
  
Part 2, “Robot Platform Construction”