tailieunhanh - McGraw-Hill - The Robot Builder's Bonanza Part 3

Tham khảo tài liệu 'mcgraw-hill - the robot builder's bonanza part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 56 COMMON ELECTRONIC COMPONENTS Tolerance Multiplier 2nd Significant figure 1st Significant figure Schematic symbol for a resiStor FIGURE Resistors use color coding to denote their value. Start from the color band nearest the end. Most resistors have four bands three for the value and one for the tolerance. Resistors are also rated by their wattage. The wattage of a resistor indicates the amount of power it can safely dissipate. Resistors used in high-load applications like motor control require higher wattages than those used in low-current applications. The majority of resistors you ll use for hobby electronics will be rated at 1 4 or even 1 8 of a watt. The wattage of a resistor is not marked on the body of the component instead you must infer it from the size of the resistor. Variable Resistors Variable resistors first introduced in Chapter 3 are more commonly known as potentiometers let you dial in a specific resistance. The actual range of resistance is determined by the upward value of the potentiometer. Potentiometers are thus marked with this upward value such as 10K 50K 100K 1M and so forth. For example a 50K potentiometer will let you dial in any resistance from 0 ohms to 50 000 ohms. Note that the range is approximate only. Potentiometers are of either the dial or slide type as shown in Fig. . The dial type is the most familiar and is used in such applications as television volume controls and electric blanket thermostat controls. The rotation of the dial is nearly 360 depending on which potentiometer you use. In one extreme the resistance through the potentiometer or pot is zero in the other extreme the resistance is the maximum value of the component. Some projects require precision potentiometers. These are referred to as multiturn pots or trimmers. Instead of turning the dial one complete rotation to change the resistance from say 0 to 10 000 ohms a multiturn pot requires you to rotate the knob three five ten even fifteen times to span the .