Introduction

For many applications, stepping motors are preferable to conventional DC motors or servomotors.

Typical advantages of stepping motors are:

• precise positioning without position sensor feedback
• small rotations without gear reduction
• high torque especially for small speed
• controllable speed (especially low speed)
• possibility to hold the positioning after moving
• instantaneous start and stop

In this Application Note we demonstrate how a small stepping motor can be directly connected to the ADB I/O through Port A.

What is a stepping motor

A stepping motor is an electrical motor which has no brush but windings (2 or 4) on the stator only.

Fig. 1 The stepping motor connected to port A of ADB I/O. The orange LEDs connected to Port B monitor the currents of the motor windings.

It turns of one step each time that at least one winding is connected or disconnected from the supply.

The number of step per revolution is variable but the most common values are 100 or 200 steps/turn meaning an angular resolution of 3.6 or 1.8 degrees.

In principle a stepping motor can turn continuously if the windings are successively powered in a well defined sequence. This is why it is often driven by an electronic interface which controls the windings.

In this Application the electronic interface is completely replaced by the Mac and the ADB I/O.

As can be seen on Fig. 1, the only parts are the ADB I/O, The motor and a battery.

How to recognise a unipolar stepping motor

There are two types of stepping motors:

• unipolar stepping motors
• bipolar stepping motors

Since this application works only with unipolar stepping motors, we give the following rules to recognise a unipolar stepping motor:
Fig. 2 Connections of 6 wires and 5 wires unipolar stepping motors

• A typical unipolar stepping motor has 5 wires.
• in some cases it may have 6 wires.
• a stepping motor which has only 4 wires is definitely a bipolar one.

The windings of a unipolar motor are connected as shown on Fig.2. They are made of two independent windings with a middle point wire on each (6 wires unipolar). Possibly the two middle points may be internally connected to a single wire called Common (C)(5 wires unipolar).
In the present application the middle points are always connected together whatever this is done inside or outside the motor, so that Fig. 2.b always applies.

What type of stepping motor to choose

Since the motor windings are driven by the ADB I/O relays, one must choose a motor compatible with the relays characteristics (max. 100 V, 500 mA).
Taking into account possible spikes due to switching-off the windings, it is recommended not to go beyond 12 V 200 mA. The motor shown on Fig. 1 has 4 windings of 75 Ohms (12 V - 160 mA/phase) and works fine when powered by a 4.5 V battery.

How to identify the wires

The first task when starting with a stepping motor is to identify the wires.
This can be done with an Ohm-Meter. Each time you find a resistance R, you are between C and one of the A terminals. If you are measuring 2R you are between two A terminals.

Fig. 3 Determination of the good colour sequence

Now all A wires are not equivalent, this is why they have a different colour. Unfortunately the colours are not universal and you will have to determine what is the "good colour sequence". The "good sequence" is the one which will make the motor to run continuously and smoothly, not going back and forth. To do that, connect the C wire to one (say +) of the pole of a small battery (4.5 V is OK). Then connect successively the 4 A wires to the other pole (Fig. 3). If the motor has always turned in the same direction you won: write quickly that the "good sequence" was brown, blue, green, red!

But if you noticed the motor going in the wrong direction while connecting the 3rd wire, this means that the 3rd wire is wrong in the sequence. Repeat the beginning of the sequence but change the 3rd colour.

Doing like this, you should quickly determine what is the "good sequence".
Note that a sequence is cyclic, which means that if:

	brown	blue	green	red	is a good sequence
then	blue	green	red	brown
or	green	red	brown	blue
or	red	brown	blue	green

are also good sequences.
This also means that no matter the colour you are starting from to test a given sequence.

Connecting the stepping motor to ADB I/O

Fig. 4 Connection of the ADB I/O to the motor

As shown on Fig.4 a, the wiring requires a common "ground" wire connected to one side of each relay screw terminal. This is done by the yellow wire directly screwed on blocks (Fig.1 and Fig. 4 b) which connects all the ADB I/O right output screws. Once the good sequence has been determined just connect the first motor wire of the motor (say brown) to channel 1, the second to channel 2 ...
Then connect the common (or the two common) wire to the + battery.
Finally connect the - battery to the yellow ground through one of the block screws.

That's all for the hardware...

You can now test that the motor moves a bit each time you set one of the channel of Port A to HIGH with the ADB I/O standard controller.

In the second part of this Note, we give some examples of HyperTalk Scripts, and briefly describe an HyperCard Applications used to run the motor.

The Software

The HyperCard Application

The software is an HyperCard stack made of 2 Cards with HyperTalk scripts.

The stack can be downloaded here. It's called ADB I/O SMC.

If you want to create your own stack, remind to install first the XCMDs for ADB I/O (see ADB I/O Manual P. 21)

The first card only contains one script to configure ADB ports A and B, and to define the sequence numbers (listN). This script is executed by clicking in the card. At the end of the script, the second card is opened.
The first card also has one field to report on errors returned by ConfigureADBIO.

The second card has 5 buttons and 6 fields.

Fig. 5 The HyperCard interface for the Stepping motor controller

Buttons

The "Forward" button is used to make the motor run forward until the shift key is pressed or the upper limit is reached.

The "Backward" button is used to make the motor run backward until the shift key is pressed or the lower limit is reached.

The " Go To OK" button is used to make the motor reach the value (target). First enter the target value in the field just above (card field 6) and click the "OK" Button.

The "switch off current" button opens all 4 relays.

The "Reset " makes the counter to reset the zero at the present position. This is to be used at the beginning or to set a new origin for angles.

Fields

The upper left field (card field 4) is a field where you enter the lower limit for the motor position. When you close the field (i.e. pressing the Enter key while the cursor is in the field, or clicking outside the field) this lower limit is put into the global variable "downstop" to be used by the button scripts.

The upper right field (card field 5) do the same for the upper limit (upstop).

The left-centre field (card field 2) is the step counter. It is cumulative for successive operations (Forward, Backward, Go To). The value of the step counter is stored in the field even after closing the stack or shutting down the Mac.

The right-centre field (card field 3) displays the number of steps made since the present movement has started, while the motor is running.

The field on the right of the "Go To button" (card field 6) is the field where you enter the target to be reached. The target is first checked to be within the limits defined in the above fields.

This Menu Button proposes 10 speeds. The speed of the motor is proportional to the speed numbers. Speed 10 corresponds to no waiting time, so the real speed of the motor is determined by the speed of your Mac. Speed 1 corresponds to approx. 1 step per second. This can be changed by changing the value of "speedfactor" in the speed button script. When you choose an item in the menu, the lower left field displays the speed number, the waiting time and the number of ticks. This is to make easier a tuning of the speed range (by changing the speedfactor) according to the speed of your Mac and to your needs.

The bottom left field (card field 1) is an information field (not for input).

The logic for the motor motion.

The principle to move the motor is simply to make the current to flow in the windings according to the following sequence:

-----------------------------------------------------
step #	1	2	3	4	------->
-----------------------------------------------------
channel 1	1	0	0	1	------->
channel 2	1	1	0	0	------->
channel 3	0	1	1	0	------->
channel 4	0	0	1	1	------->
-----------------------------------------------------
decimal N	3	6	12	9
-----------------------------------------------------

• In the above table, "step #" in the first line represent four successive steps in the currents setting.
• Each step correspond to a SetADBIO output command which is defined in the corresponding column.
• Numbers 1 and 0 in the table means current ON an OFF.
• The channel states (HIGH = 1) at a given time is given by the 4 bit number in the corresponding column. One column also represent the LEDs states of Port B (ex.: for step 2, the 2 middle lights are ON)
• "decimal N" is just the decimal value of the corresponding binary number in the column above, the Least Significant Bit being on the top.(ex.: for step #3 the currents (0011) are represented by N = 0+0+2**2+2**3 = 12). This is the number to be entered in the "SetADBIO 1,A,N" command

   

Example HyperTalk Scripts

This four steps sequence can be executed by the following script:

on mouseUp
put "3,6,12,9" into listN
repeat with k=1 to 4
put item k of listN into N
SetADBIO 1,A,N
put N into card field 1
wait 60 -- wait 1 second
end repeat
end mouseUp

Here is a script to make an arbitrary number of steps.

It uses the (j mod 4) function which returns the remainder of the division of j by 4. Note the correspondence:

j	0	1	2	3	4	5	6	7
(j mod 4)	0	1	2	3	0	1	2	3
k	1	2	3	4	1	2	3	4

since item 0 is invalid and (j mod 4) never reaches the value 4.

on mouseUp
put "3,6,12,9" into listN
put 10 into jmax
repeat with j=0 to jmax-1
put ((j mod 4)+1) into k
put item k of listN into N
SetADBIO 1,A,N
put N into card field 1
wait 60
end repeat
end mouseUp

Please let other ADB I/O users know that these archival pages are again available.