SECTION 17.1: RELAYS AND OPTOISOLATORS
1. Give one application where would you use a relay.
2. Why do we place a driver between the microcontroller and the relay?
3. What is an NC relay?
4. Why are relays that use coils called electromechanical relays?
5. What is the advantage of a solid-state relay over EMR?
6. What is the advantage of an optoisolator over an EM relay?
Answers:
1. With a relay we can use a 5 V digital system to control 12 V-120 V devices such as horns and appliances.
2. Since microcontroller I digital outputs lack sufficient current to energize the relay, we need a driver.
3. When the coil is not energized, the contact is closed.
4. When current flows through the coil, a magnetic field is created around the coil, which causes the armature to be attracted to the coil.
5. It is faster and needs less current to get energized.
6. It is smaller and can be connected to the microcontroller directly without a driver.
SECTION 17.2: STEPPER MOTOR INTERFACING
1. Give the 4-step sequence of a stepper motor if we start with 0110.
2. A stepper motor with a step angle of 5 degrees has steps per revolution.
3. Why do we put a driver between the microcontroller and the stepper motor?
Answers:
1. 0110, 0011, 1001, 1100 for clockwise; and 0110, 1100, 1001, 0011 for counterclockwise
2. 72
3. Because the microcontroller pins do not provide sufficient current to drive the stepper motor
SECTION 17.3: DC MOTOR INTERFACING AND PWM
1. True or false. The permanent magnet field DC motor has only two leads for +ve and -ve voltages.
2. True or false. Just like a stepper motor, one can control the exact angle of a DC motor's move.
3. Why do we put a driver between the microcontroller and the DC motor?
4. How do we change a DC motor's rotation direction?
5. What is stall in a DC motor?
6. True or false. PWM allows the control of a DC motor with the same phase, but different amplitude pulses.
7. The RPM rating given for the DC motor is for __________ (no-load, loaded).
Answers:
1. True
2. False
3. Since microcontroller I digital outputs lack sufficient current to drive the DC motor, we need a driver.
4. By reversing the polarity of voltages connected to the leads
5. The DC motor is stalled if the load is beyond what it can handle
6. False
7. No-load
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