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Tham khảo tài liệu 'mcgraw-hill - the robot builder's bonanza episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Control V1 V2 Control Q1 Load 0 Forward Reverse FIGURE 29.4 Power MOSFET interface. D1-D4 1N4002 Q1-Q4 n-channel MOSFET FIGURE 29.5 Discrete component H-bridge interface. V FIGURE 29.6 Packaged H-bridge interface. FIGURE 29.7 Non-inverting buffer follower interface. FIGURE 29.8 Direct connection of switch digital input. FIGURE 29.9 Switch debouncer input. Microprocessor microcontroller input INTERFACING DIGITAL INPUTS 443 FIGURE 29.10 Buffer input. Buffer or interver Schmitt trigger Shown Microprocessor microcontroller input Fig. 29.11 shows how to interface TTL 5 volt to CMOS circuits that use different power sources use this circuit even if both circuits run under 5 vdc . Fig. 29.12 shows the same concept but for translating CMOS circuits to TTL circuits that use different power sources. USING OPTO-ISOLATORS Note that in both circuits the ground connection is shared. You may wish to keep the power supplies of the inputs and control electronics totally separate. This is most easily done using opto-isolators which are readily available in IC-like packages. Fig. 29.13 shows the basic concept of the opto-isolator the source controls a light-emitting diode. The input of the control electronics is connected to a photodetector of the opto-isolator. Note that since each side of the opto-isolator is governed by its own power supply you can use these devices for simple level shifting for example changing a 5 vdc signal to 12 vdc or vice versa. ZENER DIODE INPUT PROTECTION If a signal source may exceed the operating voltage level of the control electronics you can use a zener diode to clamp the voltage to the input. Zener diodes act like valves that turn on only when a certain voltage level is applied to them. As shown in Fig. 29.14 by putting a zener diode across the V and ground of an input you can basically shunt any excess voltage and prevent it from reaching the control .
