Control Stepper Motor Using Digital Outputs

This example shows how to control a stepper motor using digital output ports.

Discover Devices Supporting Digital Output

Use daqlist to discover devices. This example uses a National Instruments® ELVIS II with ID Dev2.

d = daqlist

d =

  12×5 table

    VendorID     DeviceID                 Description                    Model             DeviceInfo     
    ________    ___________    __________________________________    _____________    ____________________

      "ni"      "cDAQ1Mod1"    "National Instruments NI 9205"        "NI 9205"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod2"    "National Instruments NI 9263"        "NI 9263"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod3"    "National Instruments NI 9234"        "NI 9234"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod4"    "National Instruments NI 9201"        "NI 9201"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod5"    "National Instruments NI 9402"        "NI 9402"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod6"    "National Instruments NI 9213"        "NI 9213"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod7"    "National Instruments NI 9219"        "NI 9219"        [1×1 daq.DeviceInfo]
      "ni"      "cDAQ1Mod8"    "National Instruments NI 9265"        "NI 9265"        [1×1 daq.DeviceInfo]
      "ni"      "Dev1"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]
      "ni"      "Dev2"         "National Instruments NI ELVIS II"    "NI ELVIS II"    [1×1 daq.DeviceInfo]
      "ni"      "Dev3"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]
      "ni"      "Dev4"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]

d{10, "DeviceInfo"}

ans = 

ni: National Instruments NI ELVIS II (Device ID: 'Dev2')
   Analog input supports:
      7 ranges supported
      Rates from 0.0 to 1250000.0 scans/sec
      16 channels ('ai0' - 'ai15')
      'Voltage' measurement type
   
   Analog output supports:
      -5.0 to +5.0 Volts,-10 to +10 Volts ranges
      Rates from 0.0 to 2857142.9 scans/sec
      2 channels ('ao0','ao1')
      'Voltage' measurement type
   
   Digital IO supports:
      39 channels ('port0/line0' - 'port2/line6')
      'InputOnly','OutputOnly','Bidirectional' measurement types
   
   Counter input supports:
      Rates from 0.1 to 80000000.0 scans/sec
      2 channels ('ctr0','ctr1')
      'EdgeCount' measurement type
   
   Counter output supports:
      Rates from 0.1 to 80000000.0 scans/sec
      2 channels ('ctr0','ctr1')
      'PulseGeneration' measurement type
   

Hardware Setup Description

This example uses a Portescap 20M020D1U motor (5 V, 18 degree unipolar stepper). The TTL signals produced by the digital I/O system are amplified by a Texas Instruments ULN2003AIN (high voltage, high current Darlington transistor array), as shown in this schematic:

Add Digital Output-Only Channels

Create a DataAcquisition and add 4 digital channels on port 0, lines 0-3. Set the measurement type to OutputOnly. These are connected to the 4 control lines for the stepper motor.

dq = daq("ni");
addoutput(dq,"Dev2","port0/line0:3","Digital")

Warning: Added channel does not support clocked sampling: clocked operations are
disabled. Only on-demand operations are allowed. 

Define Motor Steps

Refer to the Portescap motor wiring diagram describing the sequence of 4-bit patterns. Send this pattern sequentially to the motor to produce counterclockwise motion. Each step turns the motor 18 degrees. Each cycle of 4 steps turns the motor 72 degrees. Repeat this cycle five times to rotate the motor 360 degrees.

step1 = [1 0 1 0];
step2 = [1 0 0 1];
step3 = [0 1 0 1];
step4 = [0 1 1 0];

Rotate Motor

Use write to output the sequence to turn the motor 72 degrees counterclockwise.

write(dq,step1);
write(dq,step2);
write(dq,step3);
write(dq,step4);

Repeat sequence 50 times to rotate the motor 10 times counterclockwise.

for motorstep = 1:50
    write(dq,step1);
    write(dq,step2);
    write(dq,step3);
    write(dq,step4);
end

To turn the motor 72 degrees clockwise, reverse the order of the steps.

write(dq,step4);
write(dq,step3);
write(dq,step2);
write(dq,step1);

Turn Off All Outputs

After you use the motor, turn off all the lines to allow the motor to rotate freely.

write(dq,[0 0 0 0]);

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