Motors - BeagleBone - page 243

var states = [[ 1 , 0 , 0 , 0 ], [ 0 , 1 , 0 , 0 ], [ 0 , 0 , 1 , 0 ], [ 0 , 0 , 0 , 1 ]];
Whenever you step, you just index the next element in the array. If you want to go back-
ward, index the previous element.
There are two other state sequences given in the code, but they aren't ever used.
statesHiTorque is like the original states , except that it has both magnets on at
the same time, giving a stronger pull on the motor. The statesHalfStep alternates
between having one and two coils on simultaneously to give finer control in the step size:
var statesHiTorque = [[ 1 , 1 , 0 , 0 ], [ 0 , 1 , 1 , 0 ], [ 0 , 0 , 1 , 1 ], [ 1 , 0 , 0 , 1 ]];
var statesHalfStep = [[ 1 , 0 , 0 , 0 ], [ 1 , 1 , 0 , 0 ], [ 0 , 1 , 0 , 0 ], [ 0 , 1 , 1 , 0 ],
[ 0 , 0 , 1 , 0 ], [ 0 , 0 , 1 , 1 ], [ 0 , 0 , 0 , 1 ], [ 1 , 0 , 0 , 1 ]];
You can easily try either of these by assigning them to the states variable.
Notice the banded wire running from pin 8 (lower left) of the L293D to P9_7 in Fig-
ure 4-8 . This is connecting the 5 V power supply on the Bone to the L293D. The Bone
outputs 3.3 V on its GPIO pins, but the stepper motor I am using really needs 5 V. Con-
necting the 5 V in this way provides 5 V out of the L293D to the stepper motor.
NOTE
If your stepper motor requires a higher voltage (up to 12 V), you can wire an external power
supply, as shown in Figure 4-10 .