Journey of a 1000 miles begins with a single step:

We will start by setting up our breadboard, similar to the way we used it with the Light-byte.  We will leave the 2+9 pins which mate with our 26-hole connector in exactly the same place.  But now we will be adding some new stuff-- in particular, we will be using power that does not come from the parallel port itself.  It is important to remember that the bit wire electricity is extremely low power-- enough to light an LED, but certainly not enough to run a motor!  In order to decrease the likelihood of making a mistake and damaging our computers, I have found some surplus power supplies and we will be using mating connectors that ensure that power gets hooked up in the right places.  I like Power Supplies because I hate changing batteries.  I found the PS we will use as surplus-- it has just the voltages (5 and 12) that we need, and can handle the amount of current we will use (more about this later).  It is possible to damage the control computer if you are not careful with where these voltages are connected!  Fortunately, it is easy with the breadboard setup to prevent this.  But, as an extra precaution, we will ALWAYS check our circuit BEFORE connection to the computer.

Here is the breadboard map of our single stepper motor driver circuit:

And here is a picture of the breadboard up to this point.

Placement of the PS connector is crucial-- the four pins must go into the first and second column of holes (E1,E2,F1,F2).  This will ensure that 5+ is on the A1-D1 column, GND is on both the A2-D2 and F2-J2 columns, and 12+ is on the F1-J1 column.  We will put a drop of Superglue on the bottom of this connector so that it does not come out every time we plug the PS into it.

After carefully checking to make sure that we have all the parts and jumpers properly in place, we will connect our stepper to the 6-prong connector (at J27-J32).  Make sure the connection is made so that the motor's white and yellow leads are connected to the right side (J31,J32).  Turn the motor shaft-- it should feel no different than before you made the connection.

Plug the PS's AC cord into a wall outlet, and then insert the PS's plug into the PS connector that has been glued to the breadboard.  It only goes in one way (the arrow will be visible on top).  Now try to turn the motor's shaft again-- it should be stuck tight!  You may be able to overpower it into turning (this causes no harm), but there is an obvious difference.  If the shaft turns easily, then something is wrong.  Don't feel bad-- I rarely put together a circuit which works the first time!  Disconnect the PS plug and carefully double check every connection.  You will find the error if you are patient.

You will notice that after a short while your motor will get very warm.  This is normal for stepper motors, but may surprise you if you don't know this.

OK-- if everything checks out (the motor shaft is stuck), we are now ready to connect to the computer.  But first, it is a good idea to disconnect out PS from the breadboard, in case we put the 26-hole connector on wrong.  So, after removing power from the breadboard, connect the 26-hole connector to the 2+9 pins (just as with the Light-byte).  Now reconnect to the PS.  Again the motor will be frozen in place.

Now we need to write a program to send step and direction bits to our motor:

Start QBASIC, and type (in the program window):

     OUT 888,2
     OUT 888,0

Put your finger on the motor shaft and then push Sh-F5--  you have just taken your first step!
Yes, it is rather small-- do it a couple times to convince yourself that the shaft is really moving.

Now, let's use a loop to make lots of steps (steps1.bas):

     CLS
    INPUT "enter count value for speed control: ", speed
    FOR counter = 1 TO 400

    OUT 888,2
    OUT 888,0
    FOR zz = 1 TO speed: NEXT
 
    NEXT counter

Run the program (Sh-F5) and try a count value of 500.  You should see the shaft take 1 complete rotation.  Try it a few times, and pay careful attention to the starting and final position of the flat spot on the shaft (they should be exactly the same).  Try different count values-- the lower, the faster it goes (remember, the computer must count up to this number in between every step).  You will find a value that is too low-- the motor just can't step that fast.  This causes no harm to the motor or the computer, but of course this "misstepping" causes position errors and we will want to avoid it in the future when we are building robots.

How can we make it go in the other direction?  Think about that direction bit.  It is assigned to bit #0 (STEP is on bit #1).  In our program, we have left it off the whole time-- OUT 888,2  can be thought of as OUT 888, 0+2 .  But what if we try OUT 888,1+2 -- go ahead, modify the program and run it.  The shaft should complete 1 rotation in the opposite direction now.

Finally, let's do both directions, 10 times (steps2.bas):
 
    CLS
    INPUT "enter count value for speed control: ", speed

    FOR repetition = 1 to 10
 
    FOR counter = 1 TO 400
    OUT 888,2
    OUT 888,0
    FOR zz = 1 TO speed: NEXT
    NEXT counter
 
    FOR counter = 1 TO 400
    OUT 888,3
    OUT 888,0
    FOR zz = 1 TO speed: NEXT
    NEXT counter

    NEXT repetition

Notice that (if you haven't chosen a counter value too low) the shaft position at the start and end of the run is the same.  This is because we have asked the motor to make full rotations only.  But if you look at the program you will notice that our program commanded the motor to take 400 steps (not 200).  The reason is that we are running in "half-step" mode-- an option of the 5804b chip.  Although our motor is designed to take a step of 1.8 degrees (200 steps/rev), this applies only when it is run in "full-step" mode.  The 5804b chip can run in this mode, but I always choose half-step because it is smoother (results in smaller motion pixels).  Even though we will actually be taking half-steps, I will refer to these simply as steps.


next-- Dual Stepping
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Copyright © 2000 Bruce Shapiro