Embedded Systems Design with the Atmel AVR Microcontroller Part II

More documents

Recommendations

Info

194 CHAPTER 7. ATMEL AVR OPERATING PARAMETERS AND INTERFACING default:; } while(PORTC_value_masked != 0xf0); //wait for key to be released return ascii_value; } //************************************************************************* 7.3.5 SENSORS A microcontroller is typically used in control applications where data is collected, the data is assimilated and processed by the host algorithm, and a control decision and accompanying signals are provided by the microcontroller. Input data for the microcontroller is collected by a complement of input sensors. These sensors may be digital or analog in nature. 7.3.5.1 Digital Sensors Digital sensors provide a series of digital logic pulses with sensor data encoded. The sensor data may be encoded in any of the parameters associated with the digital pulse train such as duty cycle, frequency, period, or pulse rate.The input portion of the timing system may be configured to measure these parameters. An example of a digital sensor is the optical encoder. An optical encoder consists of a small plastic transparent disk with opaque lines etched into the disk surface. A stationary optical emitter and detector pair is placed on either side of the disk. As the disk rotates, the opaque lines break the continuity between the optical source and detector.The signal from the optical detector is monitored to determine disk rotation as shown in Figure 7.6. Optical encoders are available in a variety of types depending on the information desired. There are two major types of optical encoders: incremental encoders and absolute encoders. An absolute encoder is used when it is required to retain position information when power is lost. For example, if you were using an optical encoder in a security gate control system, an absolute encoder would be used to monitor the gate position. An incremental encoder is used in applications where a velocity or a velocity and direction information is required. The incremental encoder types may be further subdivided into tachometers and quadrature encoders. An incremental tachometer encoder consists of a single track of etched opaque lines as shown in Figure 7.6(a). It is used when the velocity of a rotating device is required. To calculate velocity the number of detector pulses are counted in a fixed amount of time. Since the number of pulses per encoder revolution is known, velocity may be calculated. The quadrature encoder contains two tracks shifted in relationship to one another by 90 degrees. This allows the calculation of both velocity and direction. To determine direction, one would
Ch A Ch B Figure 7.6: Optical encoder. rotating disk Detector output a) Incremental tachometer encoder b) Incremental quadrature encoder S stationary optical source and detector pair D 7.3. INPUT DEVICES 195 monitor the phase relationship between Channel A and Channel B as shown in Figure 7.6(b). The absolute encoder is equipped with multiple data tracks to determine the precise location of the encoder disk (Sick). Example: Optical encoder for motor speed measurement and control. In Chapter 8, we provide a detailed example of actively regulating the speed of a motor under various loads. An optical tachometer is used to monitor instantaneous motor speed. Based on the speed measurement, the motor is incrementally sped up or slowed down by varying the duty cycle of the motor PWM signal. 7.3.5.2 Analog Sensors Analog sensors provide a DC voltage that is proportional to the physical parameter being measured. As discussed in the analog to digital conversion chapter, the analog signal may be first preprocessed by external analog hardware such that it falls within the voltage references of the conversion subsystem. The analog voltage is then converted to a corresponding binary representation.
Page 1:
Embedded Systems Design with the At
Page 4 and 5:
iv An Introduction to Logic Circuit
Page 6 and 7:
Copyright © 2010 by Morgan & Clayp
Page 8 and 9:
ABSTRACT This textbook provides pra
Page 10 and 11:
x CONTENTS 7 6.9.3 Input Capture Mo
Page 12 and 13:
xii CONTENTS A 8.5.3 Circuit diagra
Page 15:
Preface In 2006 Morgan & Claypool P
Page 18 and 19:
138 CHAPTER 6. TIMING SUBSYSTEM x(t
Page 20 and 21:
140 CHAPTER 6. TIMING SUBSYSTEM spe
Page 22 and 23:
142 CHAPTER 6. TIMING SUBSYSTEM 6.4
Page 24 and 25: 144 CHAPTER 6. TIMING SUBSYSTEM Sim
Page 26 and 27: 146 CHAPTER 6. TIMING SUBSYSTEM in
Page 28 and 29: 148 CHAPTER 6. TIMING SUBSYSTEM The
Page 30 and 31: 150 CHAPTER 6. TIMING SUBSYSTEM Tim
Page 32 and 33: 152 CHAPTER 6. TIMING SUBSYSTEM 6.6
Page 40 and 41: 160 CHAPTER 6. TIMING SUBSYSTEM //F
Page 42 and 43: 162 CHAPTER 6. TIMING SUBSYSTEM Ope
Page 44 and 45: 164 CHAPTER 6. TIMING SUBSYSTEM TCN
Page 46 and 47: 166 CHAPTER 6. TIMING SUBSYSTEM CW
Page 48 and 49: 168 CHAPTER 6. TIMING SUBSYSTEM //6
Page 50 and 51: 170 CHAPTER 6. TIMING SUBSYSTEM } c
Page 52 and 53: 172 CHAPTER 6. TIMING SUBSYSTEM //
Page 54 and 55: 174 CHAPTER 6. TIMING SUBSYSTEM //C
Page 56 and 57: 176 CHAPTER 6. TIMING SUBSYSTEM voi
Page 58 and 59: 178 CHAPTER 6. TIMING SUBSYSTEM fan
Page 62 and 63: 182 CHAPTER 7. ATMEL AVR OPERATING
Page 116 and 117: 236 CHAPTER 8. SYSTEM LEVEL DESIGN
Page 124 and 125:
244 CHAPTER 8. SYSTEM LEVEL DESIGN
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
270 APPENDIX A. ATMEGA164 REGISTER
Page 152 and 153:
272 APPENDIX A. ATMEGA164 REGISTER
Page 154 and 155:
274 APPENDIX B. ATMEGA164 HEADER FI
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 173:
Author’s Biography STEVEN F. BARR
Page 176:
296 INDEX switch debouncing, 187 sw
show all

Embedded Systems Design with the Atmel AVR Microcontroller Part II

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?