Control De Un Motor Paso A Paso Con Pic 16F84

Controlling Stepper Motors with a PIC Microcontroller
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For applications where precise measuring of a motors' rotor position is critical, a Stepper Motor is the best choice.  Stepper motors operate diffrently from other motors; rather than voltage being applied and the rotor spinning smoothly, stepper motors turn on a series of electrical pulses to the motor's windings.  Each pulserotates the rotor by an exact degree.  These pulses are called "steps", hence the name "stepper motor".
The degrees per pulse is set in the motor's manufacturing, and is provided in the spec sheets for that motor.  They can range from ultra-fine movements of a fraction of a degree (i.e., 0.10 degrees), to larger steps (i.e. 62.5 degrees).
This article will explain the operating principals of steppermotors, and will give instructions on how to control them via a PIC16F84
How Stepper Motors Work
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Stepper motors consist of a permanent magnet rotating shaft, called the rotor, and electromagnets on the stationary portion that surrounds the motor, called the stator.  Figure 1 illustrates one complete rotation of a stepper motor.  At position 1, we can see that the rotor is beginning atthe upper electromagnet, which is currently active (has voltage applied to it).  To move the rotor clockwise (CW), the upper electromagnet is deactivated and the right electromagnet is activated, causing the rotor to move 90 degrees CW, aligning itself with the active magnet.  This process is repeated in the same manner at the south and west electromagnets until we once again reach the startingposition.
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In the above example, we used a motor with a resolution of 90 degrees or demonstration purposes.  In reality, this would not be a very practical motor for most applications.  The average stepper motor's resolution -- the amount of degrees rotated per pulse -- is much higher than this.  For example, a motor with a resolution of 5 degrees would move its rotor 5 degrees per step,thereby requiring 72 pulses (steps) to complete a full 360 degree rotation.
You may double the resolution of some motors by a process known as "half-stepping".  Instead of switching the next electromagnet in the rotation on one at a time, with half stepping you turn on both electromagnets, causing an equal attraction between, thereby doubling the resolution.  As you can see in figure 2, in the firstposition only the upper electromagnet is active, and the rotor is drawn completely to it.  In position 2, both the top and right electromagnets are active, causing the rotor to position itself between the two active poles.  Finally, in position 3, the top magnet is deactivated and the rotor is drawn all the way right.  This process can then be repeated for the entire rotation.
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There aresevral types of stepper motors.  4-wire stepper motors contain only two electromagnets, however the operation is more complicated than those with three or four magnets, because the driving circuit must be able to reverse the current after each step.  For our purposes, we will be using a 6-wire motor.
Unlike our example motors which rotated 90 degrees per step, real-world motors employ a series ofmini-poles on the stator and rotor to increase resolution.  Although this may seem to add more complexity to the process of driving the motors, the operation is identical to the simple 90 degree motor we used in our example.  An example of a multipole motor can be seen in figure 3.  In position 1, the north pole of the rotor's perminant magnet is aligned with the south pole of the stator'selectromagnet.  Note that multiple positions are alligned at once.  In position 2, the upper electromagnet is deactivated and the next one to its immediate left is activated, causing the rotor to rotate a precise amount of degrees.  In this example, after eight steps the sequence repeats.
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The specific stepper motor we are using for our experiments (ST-02: 5VDC, 5 degrees per step) has 6 wires...