All the questions asked below are
related to the Applications of PIC16F877A.
1. Make comparison between DC Motor and stepper motor?
Solution
DC Motor
A DC motor usually means a
permanent-magnet, direct-current (DC) motor of the sort used in toys, models,
cordless tools, and robots. These motors are particularly versatile because
both their speed and direction can be readily controlled; speed by the voltage
or duty cycle of their power supply, and direction by its polarity.
Stepper Motor
Stepper motors work in a similar way to
dc motors, but where dc motors have 1 electromagnetic coil to produce movement,
stepper motors contain many. Stepper motors are controlled by turning each coil
on and off in a sequence. Every time a new coil is energized, the motor rotates
a few degrees, called the step angle. Repeating the sequence causes the motor
to move a few more degrees and so on, resulting in a constant rotation of the
motor shaft.
2. For
forward and reverse motions in motor control, why 1 second of stop is inserted
before running the motor?
Solution
For forward and reverse motions, 1
second of stop is inserted before running the motor, to give time to stop the
on-going motion and its inertia (and reverse electromotive force development
and attenuation).
3. Why motor driver or relays
are used to drive the motor instead of using microcontroller to drive the motor
directly?
Solution
Because the microcontroller
couldn’t supply enough power to drive the motor directly. The maximum sink
current of PIC 16F877A is only 25mA, and the maximum voltage is only 5V.
4. The circuit in figure 4 shows the controlling of motor using
H-bridge. Explain how the microcontroller can be used the control the direction
of the motor.
Solution
Connect pin A and B to port D of
the PIC 16F877A. The motor will move forward if pin A is High and pinB is low,
vice versus, if the pin A is low and pin
B is high, the motor will moves in reverse direction. If pinA and pin B are
low, then the motor will stops.
5. Refer to figure 5, two motors are used to control front wheels and
two motors are used to control rear wheels of a car. Explain how to make the
car turns left or turns right?
Solution
Turn left or right has many different
operational options but the easiest one is: Run forward two right motors, front
and rear, and stop two left motors, front and rear for "turn left"
motion; and run forward two left motors, front and rear, and stop two right
motors, front and rear for "turn right" motion.
6. For Bi-polar stepper motor control, a
sequence of pulses must be supply to make the motor moves forward or reverse. As illustrated in figure 6 below, for
forward step turns, the correct sequence of pulses must be provided to the
coils in the order of 1 – 2 - 3 - 4 - 1. The each pulse will turn one step.
Therefore, the one sequence of pulses turns four steps, or 7.5°x4
= 30°.Write a program to move the motor forward for 30o
.
;
1 FORWARD sequence subroutine (will turn 4 steps)
;
A B 7 6 5 4 3 2 1 0 (PORTD)
;
+ + --->1 1 0 0 0 0 1 0
;
- + --->0 1 0 0 0 0 1 0
;
- - --->0 0 0 0 0 0 1 0
;
+ - --->1 0 0 0 0 0 1 0
Solution
fsequence
banksel PORTD
bcf PORTD, 0x05 ;100% power (Start Condition)
movlw B'11000010' ;1st excitation
with LED1 on
movwf PORTD
call delay10ms
call delay10ms ;this time delay determines
;how fast one step finishes
;longer delay slows the motor turn
banksel PORTD
movlw B'01000010' ;2nd excitation
with LED1 on
movwf PORTD
call delay10ms
call delay10ms
banksel PORTD
movlw B'00000010' ;3rd excitation
with LED1 on
movwf PORTD
call delay10ms
call delay10ms
banksel PORTD
movlw B'10000010' ;4th excitation
with LED1 on
movwf PORTD
movlw B'11000000' ;back to the fist pulse with
LEDs off
movwf PORTD
call delay10ms
call delay10ms
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