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# ECET 340 WEEK 7 HOMEWORK 7

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ECET 340 WEEK 7 HOMEWORK 7

1. The movable part of the solenoid is the: +2 points

2. Why is the 6N139 optoisolator used in the interfaces to devices such as large motors? +2 points

3. Calculate the number of steps per revolution for a stepper motor with a step angle of 7.5°. +2 points

4. How is stepper motor speed controlled? State any two ways a program can do this. +2 points

5. For this problem, you should look at Figure 5A on the next page as a physical example of a stepper motor. It is an example of a stepper motor with four (4) magnetic windings which are connected via an interface circuit to the HCS12 Port T pins 4, 5, 6, & 7, with an armature (rotor) that has 12 poles (combined number of North and South magnetic poles). Notice how each step rotates the rotor 30 degrees, and notice the logic states on the Port T pins going from Step 1 to Step 2. To rotate the rotor 90 degrees, you would need three (3) steps (see figure 5A for explanation).

6. Identify 2 major kinds of devices that can be used to interface a dc motor to the HCS12. +2 points

7. Given that pulses need to be delivered to a specific dc motor at the rate of 12.5 kHz to avoid vibration, write down the C statements needed to output pulses from the HCS12 to drive the at 80% of its full drive level. +2 points

8. An HCS12 timer input capture/output compare register (TC0) holds the value 0x498 when timing the period between pulses coming in from a servomotor’s optical encoder (see Figure 8A below for setup of optical encoder). Assume the counter/timer is operating at 1.0us. The encoder wheel has 6 holes. Find the motor’s speed in RPM. Show work. +2 points

9. Unidirectional dc motors often have high-voltage diode connected for reverse-bias across the motor’s input terminals. Explain why this is done.+2 points

10. What advantages do dc motors offer over stepper motors? +2 points

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