McGraw-Hill - The Robot Builder''''s Bonanza Part 7 pot

Ni-Cads, provide different nominal cell voltages. Specifically, Ni-Cad and nickel metal hydride batteries provide 1.2 volts per cell, and lead-acid batteries provide 2.0 volts per cell. To achieve higher voltages, you can link cells internally or externally (see the next section, “Increasing Battery Ratings,” for more information). By internally linking together six 1.5-volt cells, for example, the battery will output 9 volts. Nominal cell voltage is important when you are designing the battery power supplies for your robots. If you are using 1.5-volt cells, a four-cell battery pack will nominally deliver 6 volts, an eight-cell pack will nominally deliver 12 volts, and so forth. Conversely, if you are using 1.2-volt cells, a four-cell battery pack will nominally deliver 4.8 volts and an eight-cell pack will nominally deliver 9.6 volts. The lower voltage will have an effect on various robotic subsystems. For example, many microcontrollers used with robots (see Part 5 of this book) are made to operate at 5 volts and will reset—restart their program- ming—at 4.5 volts. A battery pack that delivers only 4.8 volts will likely cause problems with the microcontroller. You either need to add more cells or change the battery type to a kind that provides a higher per-cell voltage. 196 ALL ABOUT BATTERIES AND ROBOT POWER SUPPLIES Discharge (in hours) 0 1 3 4 5 6 1AH battery at: 3 hours 5 hours 7 hours Volts per cell 1.2 1.6 1.4 FIGURE 15.3 Discharge curves of a 1-AH battery at three-, five-, and seven-hour rates. Charge Discharge Volts per cell 1.2 1.6 1.4 FIGURE 15.4 The charge/discharge curves of a typical rechargeable battery. Note that the charge time is longer than the dis- charge time. Ch15_McComb 8/29/00 8:37 AM Page 196 INTERNAL RESISTANCE The internal resistance of a battery determines the maximum rate at which power can be drawn from the cells. A lower internal resistance means more power can be drawn out in less time. Lead-acid and nickel metal hydride cells are good examples of batteries that have a very low internal resistance. When comparing batteries, you don’t really need to know the actual internal resistance of the cells you use. Rather, you’ll be more concerned with the discharge curve and the maximum amp-hour ratings of the battery. Still, knowing that the battery’s internal resis- tance dictates the discharge curve and capacity of the battery will help you to design power packs for your robots. Increasing the Battery Ratings You can obtain higher voltages and current by connecting several cells together, as shown in Fig. 15.5. There are two basic approaches: ■ To increase voltage, connect the batteries in series. The resultant voltage is the sum of the voltage outputs of all the cells combined. ■ To increase current, connect the batteries in parallel. The resultant current is the sum of the current capacities of all the cells combined. Take note that when you connect cells together not all cells may be discharged or recharged at the same rate. This is particularly true if you combine two half-used batteries with two new ones. The new ones will do the lion’s share of the work and won’t last as long. Therefore, you should always replace or recharge all the cells at once. Similarly, if one or more of the cells in a battery pack is permanently damaged and can’t deliver or take on a charge like the others, you should replace it. Battery Recharging Most lead-acid and gel-cell batteries can be recharged using a 200- to 800-mA battery charger. The charger can even be a DC adapter for a video game or other electronics. Standard Ni-Cad batteries can’t withstand recharge rates exceeding 50 to 100 mA, and if you use a charger that supplies too much current you will destroy the cell. Use only a bat- tery charger designed for Ni-Cads. High-capacity Ni-Cad batteries can be charged at higher rates, and there are rechargers designed specially for them. Nickel metal hydride, rechargeable alkalines, and rechargeable lithium-ion batteries all require special rechargers. Avoid substituting the wrong charger for the battery type you are using, or you run the risk of damaging the charger and/or the battery (and perhaps caus- ing a fire). You can rejuvenate zinc batteries by placing them in a recharger for a few hours. The process is not true recharging since the battery is not restored to its original power or BATTERY RECHARGING 197 Ch15_McComb 8/29/00 8:37 AM Page 197 voltage level. The rejuvenated battery lasts about 20 to 30 percent as long as it did during its initial use. Most well-built zinc batteries can be rejuvenated two or three times before they are completely depleted. Rechargeable batteries should be periodically recharged whether they need it or not. Batteries not in regular use should be recharged every two to four months, more frequently for NiMH batteries. Always observe polarity when recharging batteries. Inserting the cells backward in the recharger will destroy the batteries and possibly damage the recharger. You can purchase ready-made battery chargers for the kind of battery you are using or build your own. The task of building your own is fairly easy because several manufactur- ers make specialized integrated circuits just for recharging batteries. These ICs provide all the necessary voltage and current protective mechanisms to ensure that the battery is prop- erly charged. For example, you can use the Unitrode UC/2906 and UC/3906 from Texas Instruments to build an affordable charger for sealed lead-acid and gelled electrolyte bat- teries. Similarly, the MAX712 from Maxim lets you construct a flexible fast recharger for NiMH batteries. These and other specialty ICs are not always widely available, so you may 198 ALL ABOUT BATTERIES AND ROBOT POWER SUPPLIES A. Parallel connection 2X current + - + - B. Series connection 2X voltage + - + - Battery 1 Battery 2 Battery 1 Battery 2 FIGURE 15.5 Wiring batteries to increase ratings. a. Parallel connection increases cur- rent; b. Series connection increases voltage. Ch15_McComb 8/29/00 8:37 AM Page 198 need to check several sources before you find them. However, the search is well worth the time because of the cost and construction advantages these chips can provide. Ni-Cad Disadvantages Despite their numerous advantages, Ni-Cad batteries have a few peculiarities you’ll want to consider when designing your robot power system. The most annoying problem is the “mem- ory effect” we discussed earlier in this chapter. Not all battery experts agree that Ni-Cads still suffer from this problem, but most anyone who has tried to use Ni-Cads has experienced it in one form or another. For various reasons we won’t get into, the discharge curve of Ni-Cad batteries is sometimes altered. The net effect is that the battery won’t last as long on a full charge as it should. This so-called memory effect can be altered in two ways: ■ The dangerous way. Short the battery until it’s dead. Recharge it as usual. Some batter- ies may be permanently damaged by this technique. ■ The safe way. Use the battery in a low-current circuit, like a flashlight, until it is dead. Recharge the battery as usual. You must repeat this process a few times until the mem- ory effect is gone. The best way to combat memory effect is to avoid it in the first place. Always fully dis- charge Ni-Cad batteries before charging them. If you don’t have a flashlight handy, build yourself a discharge circuit using a battery holder and a flashlight bulb. The bulb acts as a “discharge” indicator. When it goes out, the batteries are fully discharged. The other disadvantage is that the polarity of Ni-Cads can change—positive becomes negative and vice versa—under certain circumstances. Polarity reversal is common if the battery is left discharged for too long or if it is discharged below 75 or 80 percent capacity. Excessive discharging can occur if one or more cells in a battery pack wears out. The adjacent cells must work overtime to compensate, and discharge themselves too fast and too far. You can test for polarity reversal by hooking the battery to a volt-ohm meter (remove it from the pack if necessary). If you get a negative reading when the leads are connected properly, the polarity of the cell is reversed. You can sometimes correct polarity reversal by fully charging the battery (connecting it in the recharger in reverse), then shorting it out. Repeat the process a couple of times if necessary. There is about a fifty-fifty chance that the battery will survive this. The alternative is to throw the battery out, so you actually stand to lose very little. Recharging the Robot You’ll probably want to recharge the batteries while they are inside the robot. This is no problem as long as you install a connector for the charger terminals on the outside of the robot. When the robot is ready for a charge, connect it to the charger. Ideally, the robot should be turned off during the charge period, or the batteries may never recharge. However, turning off the robot during recharging may not be desirable, as this will end any program currently running in the robot. There are several schemes you NI-CAD DISADVANTAGES 199 Ch15_McComb 8/29/00 8:37 AM Page 199 can employ that will continue to supply current to the electronics of the robot yet allow the batteries to charge. One way is to use a relay switchout. In this system, the external power plug on your robot consists of four terminals: two for the battery and two for the electron- ics. When the recharger is plugged in, the batteries are disconnected from the robot. You can use relays to control the changeover or heavy-duty open-circuit jacks and plugs (the ones for audio applications may work). While the batteries are switched out and being recharged, a separate power supply provides operating juice to the robot. Battery Care Batteries are rather sturdy little creatures, but you should follow some simple guidelines when using them. You’ll find that your batteries will last much longer, and you’ll save yourself some money. ■ Store new batteries in the fresh food compartment of your refrigerator (not the freezer). Put them in a plastic bag so if they leak they won’t contaminate the food. Remove them from the refrigerator for several hours before using them. ■ Avoid using or storing batteries in temperatures above 75°F or 80°F. The life of the bat- tery will be severely shortened otherwise. Using a battery above 100°F to 125°F caus- es rapid deterioration. ■ Unless you’re repairing a misbehaving Ni-Cad, avoid shorting out the terminals of the battery. Besides possibly igniting fumes exhausted by the battery, the sudden and intense current output shortens the life of the cell. ■ Keep rechargeable batteries charged. Make a note when the battery was last charged. ■ Fully discharge Ni-Cads before charging them again. This prevents memory effect. Other rechargeable battery types (nickel metal hydride, rechargeable alkaline, lead-acid, etc.) don’t exhibit a memory effect and can be recharged at your convenience. ■ Given the right circumstances all batteries will leak, even the “sealed” variety. When they are not in use, keep batteries in a safe place where leaked electrolyte will not cause damage. Remove batteries from their holder when they are not being used. Power Distribution Now that you know about batteries, you can start using them in your robot designs. The most simple and straightforward arrangement is to use a commercial-made battery holder. Holders are available that contain from two to eight AA, C, or D batteries. The wiring in these holders connects the batteries in series, so a four-cell holder puts out 6 volts (1.5 times 4). You attach the leads of the holder (red for positive and black for ground or nega- tive) to the main power supply rail in your robot. If you are using a gel-cell or lead-acid battery you would follow a similar procedure. FUSE PROTECTION Flashlight batteries don’t deliver extraordinary current, so fuse protection is not required on the most basic robot designs. Gel-cell, lead-acid, and high-capacity Ni-Cad batteries 200 ALL ABOUT BATTERIES AND ROBOT POWER SUPPLIES Ch15_McComb 8/29/00 8:37 AM Page 200 can deliver a most shocking amount of current. In fact, if the leads of the battery acciden- tally touch each other or there is a short in the circuit the wires may melt and a fire could erupt. Fuse protection helps eliminate the calamity of a short circuit or power overload in your robot. As illustrated in Fig. 15.6, connect the fuse in line with the positive rail of the battery, as near to the battery as possible. You can purchase fuse holders that connect directly to the wire or that mount on a panel or printed circuit board. Choosing the right value of fuse can be a little tricky, but it is not impossible. It does require that you know how much current your robot draws from the battery during normal and stalled motor operation. You can determine the value of the fuse by adding up the current draw of each separate subsystem, then tack on 20 to 25 percent overhead. Let’s say that the two drive motors in the robot draw 2 amps each, the main circuit board draws 1 amp, and the other small motors draw 0.5 amp each (for a total of, perhaps, 2 amps). Add all these up and you get 7 amps. Installing a fuse with a rating of at least 7 amps at 125 volts will help assure that the fuse won’t burn out prematurely during normal operation. Adding that 20 to 25 percent margin calls for an 8- to 10-amp fuse. Recall from earlier in this chapter that motors draw excessive current when they are first started. You can still use that 8- to 10-amp fuse, but make sure it is the slow-blow type. Otherwise, the fuse will burn out every time one of the heavy-duty motors kick in. Fuses don’t come in every conceivable size. For the sake of standardization, choose the regular 1 1/4-inch-long-by-1/4-inch-diameter bus fuses. You’ll have an easier job finding fuse holders for them and a greater selection of values. Even with a standard fuse size, there is not much to choose from past 8 amps, other than 10, 15, and 20 amps. For values over 8 amps, you may have to go with ceramic fuses, which are used mainly for microwave ovens and kitchen appliances. MULTIPLE VOLTAGE REQUIREMENTS Some advanced robot designs require several voltages if they are to operate properly. The drive motors may require 12 volts, at perhaps two to four amps, whereas the electronics require ϩ5, and perhaps even Ϫ5 volts. Multiple voltages can be handled in several ways. The easiest and most straightforward is to use a different set of batteries for each main POWER DISTRIBUTION 201 To robot subsytems Fuse Battery + - To motors, regulators, etc. FIGURE 15.6 How to install a fuse in line with the battery and the robot electronics or motor. Ch15_McComb 8/29/00 8:37 AM Page 201 subsection. The motors operate off one set of large lead-acid or gel-cell batteries; the elec- tronics are driven by smaller capacity Ni-Cads. This approach is actually desirable when the motors used in the robot draw a lot of cur- rent. Motors naturally distribute a lot of electrical noise throughout the power lines, noise that electronic circuitry is extremely sensitive to. The electrical isolation that is provided when you use different batteries nearly eliminates problems caused by noise (the remain- der of the noise problems occur when the motor commutators arc, causing RF interfer- ence). In addition, when the motors are first started the excessive current draw from the motors may zap all the juice from the electronics. This “sag” can cause failed or erratic behavior, and it could cause your robot to lose control. The other approach to handling multiple voltages is to use one main battery source and “step” it down (sometimes up) so it can be used with the various components in the sys- tem. This is called DC-DC conversion, and you can accomplish it by using circuits of your own design or by purchasing specialty integrated circuit chips that make the job easier. One 12-volt battery can be regulated (see “Voltage Regulation” later in this chapter) to just about any voltage under 12 volts. The battery can directly drive the 12-volt motors and, with proper regulation, supply the ϩ5-volt power to the circuit boards. Connecting the batteries judiciously can also yield multiple voltage outputs. By con- necting two 6-volt batteries in series, as shown in Fig. 15.7, you get ϩ12 volts, ϩ6 volts, and Ϫ6 volts. This system isn’t nearly as foolproof as it seems, however. More than likely, the two batteries will not be discharged at the same rate. This causes extra current to be drawn from one to the other, and the batteries may not last as long as they might otherwise. If all of the subsystems in your robot use the same batteries, be sure to add sufficient filtering capacitors across the positive and negative power rails. The capacitors help soak up excessive current spikes and noise, which are most often contributed by motors. Place the capacitors as near to the batteries and the noise source as possible. Exact values are not critical, but they should be over 100 µF—even better is 1000 to 3000 µF. Be certain the capacitors you use are rated at the proper voltage (25 to 35 volts is fine). Using an under- rated capacitor will burn it out and possibly cause a short circuit. You should place smaller value capacitors, such as 0.1 µF, across the positive and neg- ative power rails wherever power enters or exits a circuit board. As a general rule, you 202 ALL ABOUT BATTERIES AND ROBOT POWER SUPPLIES + - +12vdc +6vdc or -6vdc 6-volt battery + - 6-volt battery FIGURE 15.7 Various voltage tap-offs from two 6-volt batteries. This is not an ideal approach (the batteries will discharge at dif- ferent rates), but it works in a pinch. Ch15_McComb 8/29/00 8:37 AM Page 202 should add these “decoupling” capacitors beside clocked logic ICs, particularly flip-flops and counters. A few linear ICs, such as the 555 timer, need decoupling capacitors, or the noise they generate through the power lines can ripple through to other circuits. If many ICs are on the board, you can usually get by with adding one 0.1 µF decoupling capacitor for every three or four chips. SEPARATE BATTERY SUPPLIES Most hobby robots now contain computer-based control electronics of some type. The computer requires a specific voltage (called regulation, discussed in the next section), and it expects the voltage to be “clean” and free of noise and other glitches. A common prob- lem in robotic systems is that the motors cause so-called sags and noise in the power supply system, which can affect the operation of the control electronics. You can largely remedy this by using separate battery supplies for the motors and the electronics. Simply join the ground connection for the supplies together. With this setup, the motors have one unregulated power supply, and the control elec- tronics have their own regulated power supply. Even if the motors turn on and off very rapidly this approach will minimize sags and noise on the electronics side. It’s not always possible to have separate battery supplies, of course. In these cases, use the capacitor fil- tering techniques described in the earlier “Multiple Voltage Requirements” section. The large capacitors that are needed to achieve good filtering between the electronics and motor sections will increase the size of your robot. A 2200 µF capacitor, for example, may measure 3/4 inch in diameter by over an inch in height. You should plan for this in your design. Voltage Regulation Many types of electronic circuits require a precise voltage or they may be damaged or act erratically. Generally, you provide voltage regulation only to those components and circuit boards in your robot that require it. It is impractical to regulate the voltage for the entire robot as it exits the battery. You can easily add solid-state voltage regulators to all your electronic circuits. They are easy to obtain, and you can choose from among several styles and output capacities. Two of the most popular voltage regulators, the 7805 and 7812, pro- vide ϩ5 volts and ϩ12 volts, respectively. You connect them to the “ϩ” and “Ϫ” (ground) rails of your robot, as shown in Fig. 15.8 (refer to the parts list in Table 15.1). Other 7800 series power regulators are designed for ϩ15, ϩ18, ϩ20, and ϩ24 volts. The 7900 series provide negative power supply voltages in similar increments. The current capacity of the 7800 and 7900 series that come in the TO-220 style transistor packages (these can often be identified as they have no suffix or use a “T” suffix in their part num- ber), is limited to less than one amp. As a result, you must use them in circuits that do not draw in excess of this amount. Other regulators are available in a more traditional TO-3-style transistor package (“K” suffix) that offers current output to several amps. The “L” series regulators come in the small TO-92 transistor packages and are designed for applications that require less than about 500 mA. Other regulators of interest: VOLTAGE REGULATION 203 Ch15_McComb 8/29/00 8:37 AM Page 203 ■ The 328K provides an adjustable output to 5 volts, with a maximum current of 5A (amperes). ■ The 78H05K offers a 5-volt output at 5A. ■ The 78H12K offers a 12-volt output at 5A. ■ The 78P05K delivers 5 volts at 10 amps. SWITCHING VOLTAGE REGULATION All of the regulators described in the last section are the linear variety. They basically take an incoming voltage and clamp it to some specific value. Linear regulation isn’t very effi- cient; a lot of energy is wasted in heat from the regulator. This inefficiency is particularly notable in battery-powered systems, where the current capacity and the battery life are limited. An alternative to linear regulators is to use a switching (or switching-mode) voltage regulator, which exhibits better efficiencies. Most high-tech electronics equipment now use switching power supplies, especially since single-IC switching voltage regulators are now so common and inexpensive. Maxim, Texas Instruments, Dallas Semiconductor, and many other companies are actively involved in the design and sale of switching voltage regulators. See Appendix B, “Sources,” and Appendix C, “Robot Information on the Internet,” for more information on these and other companies offering power supply ICs and circuits. A good example of a switching voltage regulator is the MAX638, from Maxim. With just a few added parts (a typical circuit, taken from the MAX638’s data sheet, is shown in Fig. 15.9; refer to the parts list in Table 15.2), you can build a simple, compact, inex- pensive, and efficient voltage regulator. The chip can also be used as a low-battery detector. See “Battery Monitors” later in this chapter for more information on low- battery detection. 204 ALL ABOUT BATTERIES AND ROBOT POWER SUPPLIES IN OUT GND 100 µF Voltage Regulator To electronics + Decoupling/filtering capacitors Positive supply rail (from battery) Negative supply rail (from battery) 0.1 µF C1 C3 IC1 0.1 µF C2 FIGURE 15.8 Three-terminal linear voltage regulators, like the 7805, can be used to provide stable voltages for battery-pow- ered robots. The capacitors help filter (smooth out) the voltage. TABLE 15.1 PARTS LIST FOR ϩ 5-VOLT BATTERY REGULATOR. IC1 7805 linear voltage regulator C1 100 ␮F electrolytic capacitor C2, C3 0.1 ␮F tantalum capacitor Ch15_McComb 8/29/00 8:37 AM Page 204 ZENER VOLTAGE REGULATION A quick and inexpensive method for providing a semiregulated voltage is to use zener diodes, as shown in Fig. 15.10. With a zener diode, current does not begin to flow through the device until the voltage exceeds a certain level (called the breakdown voltage). Voltage over this level is then “shunted” through the zener diode, effectively limiting the voltage to the rest of the circuit. Zener diodes are available in a variety of voltages, such as 3.3 volts, 5.1 volts, 6.2 volts, and others. Zener diodes are also rated by their tolerance (1 percent and 5 percent are common) and their power rating, in watts. For low-current applications, a 0.3- or 0.5-watt zener should be sufficient; higher currents require larger 1-, 5-, and even 10-watt zeners. Note the VOLTAGE REGULATION 205 +Vm +BV 6 +Vs R1 R2 100k⍀ 3 2 LB1 LB0 N + - + - + - LOW BATTERY COMPARATOR LOW BATTERY OUTPUT ERROR COMPARATOR +1.31V BANDGAP REFERENCE 65kHz OSC MODE SELECT COMPARATOR GND 50mV + + P5LX D1 1N4148 220␮H 100␮F0.1␮F +5VOUT VOUT 1 COMP B VFB 7 4 FIGURE 15.9 The Maxim MAX638 is among several high-efficiency voltage regu- lators available. The MAX638 is most commonly used to provide regulated ϩ5 volts, but it can also be adjusted using external com- ponents to provide other voltages. TABLE 15.2 PARTS LIST FOR MAXIM MAX638 SWITCHING POWER SUPPLY. IC1 MAX 638 (Maxim) R1 120K resistor R2 47K–100K resistor C1 0.1 ␮F ceramic capacitor C2 100 ␮F electrolytic capacitor D1 1N4148 diode L1 220 ␮H inductor All resistors have 5 or 10 percent tolerance, 1/4-watt. Ch15_McComb 8/29/00 8:37 AM Page 205 [...]... must HOW THE CIRCUIT WORKS Here’s how the circuit works The incoming AC is routed to the AC terminals of the transformer The “hot” side of the AC is connected through a 2-amp slow-blow fuse and a single-pole, single-throw (SPST) toggle switch With the switch in the off (open) position, the transformer receives no power so the supply is off The 1 17 VAC is stepped down to the secondary voltage of the transformer... in Fig 16.12 The robot can be steered in a circle just slightly larger than the width of the machine Be careful about the wheelbase of the robot (distance from the back wheels to the front steering wheel) A short base will cause instability in turns, and the robot will tip over opposite the direction of the turn Tricycle-steered robots must have a very accurate steering motor in the front The motor must... a design in either of two ways: I Reduce the height of the robot to better match the area of the base, or I Increase the area of the base to compensate for the height of the robot (There is also a third method called dynamic balance Here, mechanical weight is dynamically repositioned to keep the robot on even kilter These systems are difficult to engineer and, in any event, are beyond the scope of this... keep in mind include the following: I The wider the wheels, the more the robot will tend to stay on course With very narrow I I I I wheels, the robot may have a tendency to favor one side or the other and will trace a slow curve instead of a straight line Conversely, if the wheels are too wide, the friction created by the excess wheel area contacting the ground may hinder the robot s ability to make... stop the left motor, the robot turns to the left By reversing the motors relative to one another, the robot turns by spinning on its wheel axis (“turns in place”) You use this forward-reverse movement to make “hard” or sharp right and left turns CENTER-LINE DRIVE MOTOR MOUNT You can place the wheels—and hence the motors—just about anywhere along the length of the platform If they are placed in the middle,... monitor using a 4.3-volt quarter-watt zener diode R1 sets the trip point When in operation, the LED winks off when the voltage drops below the setpoint To use the monitor, set R1 (which should be a precision potentiometer, 1 or 3 turn) when the batteries to your robot are low Adjust the pot carefully until the LED just winks off Recharge the batteries The LED should now light Another, more “scientific”... connect them as shown within the dotted box When using the bridge rectifier, be sure to connect the leads to the proper terminals The two terminals marked with a “~” connect to the transformer The “ϩ” and “Ϫ” terminals are the output and must connect as shown in the schematic in Fig 15.18 Use a 5-volt, 1-amp regulator—a 78 05—to maintain the voltage output at a steady 5 volts S1 BR1 4A F1 2A IC1 78 05 ~... center-line robot Steering circle for front-drive robot FIGURE 16 .7 The steering circle of a robot with centerline and front-drive mounted motors Ch16_McComb 8/18/00 2:14 PM Page 228 228 ROBOT LOCOMOTION PRINCIPLES Base Drive wheel Caster Path Suspension Path FIGURE 16.8 The height of the caster with respect to the drive wheels will greatly influence the robot s traction and maneuverability A spring-loaded... shown in the schematic (note the polarity), the ripple at the output of the power supply is negligible LED1 and R1 form a simple indicator The LED will glow when the power supply is on Remember the 220ohm resistor The LED will burn up without it The output terminals are insulated binding posts Don’t leave the output wires bare The wires may accidentally touch one another and short the supply Solder the. .. voltages above the normal supply An example are the “high-side” power MOSFET transistors in an H-bridge driver circuit You can use the circuit shown in Fig 15.13 (refer to the parts list in Table 15.4) to double the supply voltage to provide the desired voltage The current level at the output is very low, but it should be enough to be used as a high-voltage pulse The circuits described in the previous . The current capacity of the 78 00 and 79 00 series that come in the TO-220 style transistor packages (these can often be identified as they have no suffix or use a “T” suffix in their part num- ber),. BATTERIES AND ROBOT POWER SUPPLIES + - +12vdc +6vdc or -6 vdc 6-volt battery + - 6-volt battery FIGURE 15 .7 Various voltage tap-offs from two 6-volt batteries. This is not an ideal approach (the batteries. want to recharge the batteries while they are inside the robot. This is no problem as long as you install a connector for the charger terminals on the outside of the robot. When the robot is ready