Page 246 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

Port B Output (decimal)
Q1 Q2
Q3
Q4
1
—
—
On — Table 10.3 Full-Step Transistors
— On — — 2
— — On — 4
— — — On 8
and simple to show how easy it is to get a stepper motor moving.
Table 10.3 shows that each step in the sequence turns on one tran-
sistor. Use Table 10.3 to follow the logic in the PICBASIC program.
When you reach the end of the table, the sequence repeats starting
back at the top of the table.
‘Stepper Motor Controller
Symbol TRISB = 134 ‘Initialize TRISB to 134
Symbol PortB = 6 ‘Initialize portb to 6
symbol ti = b6 ‘Initial ti delay
ti = 25 ‘Set delay to 25 ms
Poke TRISB,0 ‘Set PORTB lines output
start: ‘Forward rotation sequence
poke portb,1 ‘Step 1
pause ti ‘Delay 225
poke portb,2 ‘Step 2
pause ti ‘Delay
poke portb,4 ‘Step 3
pause ti ‘Delay
poke portb,8 ‘Step 4
pause ti ‘Delay
goto start ‘Do again
One rotation

Using whole steps, the stepper motor requires 200 pulses to com-
plete a single rotation (360 degrees/1.8 degrees per step). Having
the PIC microcontroller count pulses allows it to control and position
the stepper motor’s rotor.

Second PICBASIC program

This second PICBASIC program is far more versatile. The user can
modify programmed parameters (time delay) as the program is run-
ning using one of the four switches connected to port A. Pressing
switch 1 (SW1) lengthens the delay pause between steps in the
sequence and subsequently makes the stepper motor rotate
slower. Pressing SW2 has the opposite effect. If you press SW3,

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