Embedded Systems Design with the Atmel AVR Microcontroller Part II

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216 CHAPTER 7. ATMEL AVR OPERATING PARAMETERS AND INTERFACING { if(column==64) { lcd_select_side(RIGHT); lcd_instruction_write(X_ADRESS | page); lcd_instruction_write(Y_ADRESS); } lcd_data_write(0x00); } } } //************************************************************************* 7.4.8 HIGH POWER DC DEVICES A number of direct current devices may be controlled with an electronic switching device such as a MOSFET. Specifically, an N-channel enhancement MOSFET (metal oxide semiconductor field effect transistor) may be used to switch a high current load on and off (such as a motor), using a low current control signal from a microcontroller as shown in Figure 7.17(a). The low current control signal from the microcontroller is connected to the gate of the MOSFET. The MOSFET switches the high current load on and off, consistent with the control signal. The high current load is connected between the load supply and the MOSFET drain. It is important to note that the load supply voltage and the microcontroller supply voltage do not have to be at the same value. When the control signal on the MOSFET gate is logic high, the load current flows from drain to source. When the control signal applied to the gate is logic low, no load current flows. Thus, the high power load is turned on and off by the low power control signal from the microcontroller. Often the MOSFET is used to control a high power motor load. A motor is a notorious source of noise. To isolate the microcontroller from the motor noise, an optical isolator may be used as an interface as shown in Figure 7.17(b). The link between the control signal from the microcontroller to the high power load is via an optical link contained within a Solid State Relay (SSR). The SSR is properly biased using techniques previously discussed. 7.5 DC SOLENOID CONTROL The interface circuit for a DC solenoid is provided in Figure 7.18. A solenoid provides a mechanical insertion (or extraction) when asserted. In the interface, an optical isolator is used between the microcontroller and the MOSFET used to activate the solenoid. A reverse biased diode is placed
from micro Gate Drain Source a) N-channel enhance MOSFET Figure 7.17: MOSFET circuits. V DD load I load 7.5. DC SOLENOID CONTROL 217 b) solid state relay with optical interface across the solenoid. Both the solenoid power supply and the MOSFET must have the appropriate voltage and current rating to support the solenoid requirements. from micro I 7404 V DD R Solid State Relay Figure 7.18: Solenoid interface circuit. R G G D MOSFET S DC solenoid supply voltage I LOAD protection diode
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Embedded Systems Design with the At
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iv An Introduction to Logic Circuit
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Copyright © 2010 by Morgan & Clayp
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ABSTRACT This textbook provides pra
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x CONTENTS 7 6.9.3 Input Capture Mo
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xii CONTENTS A 8.5.3 Circuit diagra
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Preface In 2006 Morgan & Claypool P
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138 CHAPTER 6. TIMING SUBSYSTEM x(t
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140 CHAPTER 6. TIMING SUBSYSTEM spe
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266 CHAPTER 8. SYSTEM LEVEL DESIGN
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268 CHAPTER 8. SYSTEM LEVEL DESIGN
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270 APPENDIX A. ATMEGA164 REGISTER
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272 APPENDIX A. ATMEGA164 REGISTER
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274 APPENDIX B. ATMEGA164 HEADER FI
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Author’s Biography STEVEN F. BARR
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296 INDEX switch debouncing, 187 sw
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Embedded Systems Design with the Atmel AVR Microcontroller Part II

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