I was wondering if it is possible to tap into the signal either on the low power side (between motion controller and the stepper motor driver) or on the high power side (between the stepper motor driver and the step motor itself).

I have a 4 axis motion controller, from which I am trying to take the signal off of the Z axis and use it to drive a optocoupler that would be in Darlington configuration with a bigger transistor to drive a relay.

Stepper motor is a big one Leadshine 86HS120 High Performance 2-Phase NEMA 34 Hybrid Stepper Motor, 70 V / 5-7 A.

Is this "tap" going to degrade the signal in any way, and if not - what should be required (I was thinking about some rectification and smoothing circuit to drive the optocoupler LED).

Excuse for my lack of knowledge in this field and please share your thoughts. Any word of advice is appreciated. Thank you.

Update #1:

Before anything, thank you everyone for engaging. Secondly, I see your point - so I am including the details for easier understanding.

This is a commercially made industrial laser cutting machine. It uses two axes (X, Y) for laser cutting head and Z axis for moving the belt "bed" underneath the material (textile material that is fed from a spool on the right side of the machine, goes trough the machine and out the left side).

There is an additional table to the left side of the machine, that needs to rotate its belt when the belt inside the machine rotates, so the cut material flows out without wrinkling.

This side table is the issue. It has its relay that is connected to PIN 6 of the general purposes "OUT" port of the controller, and should get a command to start the side table belt when Z axis is engaged. But it does not - and the manufacturer is unable to debug it for a long time.

Thus a need for alternative solution arised from. To make a circuit that would take Z axis signal and trigger a relay, bypassing the port "OUT6".

Controller model is AMC6340, and the driver model is DM856.

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  • \$\begingroup\$ No but you must define the function for direction and threshold as you have 4 signals or 2 currents to convert to 1 \$\endgroup\$ May 6, 2020 at 21:54
  • \$\begingroup\$ I'm curious as to what you are wanting to use the relay for being that a stepper signal is a square wave? \$\endgroup\$
    – Ron Beyer
    May 6, 2020 at 22:01
  • \$\begingroup\$ It might be that your stepper driver takes Step, Dir, Enable inputs, if so it is pretty easy to tap that signal.. that said: 1 - this sounds like a XY problem - you might want to desbribe your actual problem, not the problem you found in your solution, 2 - Would be nice if you could specify which motion controller/driver you are using so that we know the signals you can tap. \$\endgroup\$
    – Wesley Lee
    May 6, 2020 at 23:16
  • \$\begingroup\$ Thank you all. I updated the thread a little bit. If wiring diagram is needed, I think I could follow up on it and provide that as well. \$\endgroup\$
    – nexus.so
    May 7, 2020 at 6:59

2 Answers 2


The simplest solution is to feed the Z axis PUL/DIR/5V signals to two stepper drivers: one to drive the actual Z axis, and another to drive the side table stepper. If the direction is wrong, just swap polarity of one side table motor coil. Hopefully that will work.

If the side table is not a stepper but a simple DC motor, then things are even simpler: you can use the pulse signal from the Z axis output to drive an enable signal to a DC motor speed controller - one of those little boards that you can buy from China should do the trick.

The way I'd set up this pulse-to-on/off-signal conversion is by the following circuit:


simulate this circuit – Schematic created using CircuitLab

The circuit in the dashed line box is a model of an optocoupler. Probably any optocoupler with a transistor output will do in this application.

The circuit on the left drives the optocoupler from the Z PUL signal, without loading the signal down - transistor Q1 buffers the signal.

The circuit on the right is a relay driver with a "low pass" response. C1 is sufficient for 4kHz stepper pulse rate from the controller. If the rate is lower, increase C1 up to a couple microfarads as needed. This will determine how long the relay will stay on after the Z axis stepper has stopped.

BUF1 is a Schmitt trigger input logic gate. Q2 drives a 24V (max) relay.

The circuit on the right should be powered from the same 24V and ground that is used for the relays. The relay coil should be connected as shown.


AS the DM856 has optically isolated inputs, I see no reason why you could not connect your DM856 to the controller Z output in parallel with the existing Z driver

  • \$\begingroup\$ Uh, oh ... DM856 is the current driver hooked to the controller. I'll try to make a wiring diagram, for easier understanding of how everything is connected together. TY nonetheless for stepping in and replying. \$\endgroup\$
    – nexus.so
    May 7, 2020 at 9:30
  • \$\begingroup\$ you'll need some sort of stepper driver to control the conveyor motor. \$\endgroup\$ May 7, 2020 at 9:40

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