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I'm working on a project that requires a stepper motor and that motor is controlled by a Siemens S7 1200 PLC.

The motor in question: http://www.omc-stepperonline.com/nema-34-cnc-stepper-motor-5nm708ozin-30a-34hs383008s-p-32.html

The driver: http://www.omc-stepperonline.com/bipolar-stepper-motor-driver-max-4a-current-40vdc-input-16-subdivision-st6600-p-246.html

My question is how to wire the S7 1200 outputs to the motor controller. The 1200 has the required pulse outputs and I believe I can figure out most of the software aspect. I'm just not sure how the 1200's outputs correlate to the pulse, direction, and enable inputs on the controller.

Thanks in advance.

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  • \$\begingroup\$ Tristan - FYI, I have found that the ENABLE signal defaults to the enabled state with no connections. So while you are doing your initial testing you can leaving the ENABLE signal disconnected if that simplifies your early testing. \$\endgroup\$ – Entrepreneur May 25 '17 at 14:58
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The inputs on the stepper driver module are optical isolators, in other words, LEDs. The manufacturer provided connections to both sides of the input, but you can tie one side to +5V (from the S7) as indicated on the driver module silk-screen writing. To actuate the control signal the S7 provides a logic low, 0V, or ground to the other input. Your control signal is in effect providing power to turn on the internal LED which passes the control signal through optically while maintaining electrical isolation.

If +5 volts in unavailable +24 vdc could be used with a 2.2K ohm resistor in line to limit the LED current to about 10 mA. Also you may vary the parameters to accommodate the output choices available from the S7. The goal is to provide about 10 mA through the opto-isolator to turn the LED on and off under your control.

Mechanical relay outputs for the S7 PLC will not work though because relay outputs can bounce a few times in a millisecond and the driver will interpret that as multiple motor steps. Solid state outputs will work. Digital outputs are the most common method.

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  • \$\begingroup\$ Updated my answer to include alternatives to a 5 vdc supply. \$\endgroup\$ – Entrepreneur May 24 '17 at 15:34
  • \$\begingroup\$ So to be clear, I will need the outputs from the s7 to go to the "-" input for the pulse and direction and then I could use a 24Vdc power supply with 2.2k ohm resistors on the "+" for pulse and direction. Is this correct? \$\endgroup\$ – Tristan Abrams May 24 '17 at 16:42
  • \$\begingroup\$ Yes. But you don't need to use an additional power supply. Whatever DC voltage is readily available will work. I only chose 24vdc because when I googled "S7 1200" some of the photos showed that 24 vdc was available at some of the terminals. Optionally, you could fix the "-" terminal of the driver module to ground and pulse the "+" terminal high through a 2.2k ohm resistor. \$\endgroup\$ – Entrepreneur May 24 '17 at 19:08

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