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OptoIsolation of stepper motor drivers

Posted: Fri Feb 15, 2019 6:54 am
by Phaedrus
Hello all,
I have a query for the electronics experts here.
I am making a control board of my own,which will run the GRBL firmware. Am powering my setup with a 24V SMPS,i.e. the steppers and the spindle motor.An isolated DC-DC converter will give the 5V needed for the uC and control electronics.
My query is : Is it useful to opto isolate the link between the uC and the stepper drivers? So far I have been running my machine with an Arduino and Protoneer shield,for about 15min runs with no problems.Has anyone had any problems which were solved,by optoisolating this part of the circuit.
Any links/suggestions would be great.

Re: OptoIsolation of stepper motor drivers

Posted: Thu Mar 14, 2019 8:39 pm
by GurneyHalleck
It is generally good practice to opto-isolate higher voltages to avoid accidentally exposing your control electronics to the higher voltage.
I have included the schematic for a relay board that I use with my Arduino.

The relay board came equipped with an Opto-Isolator, the 4-pin U1. 5V from the Arduino is connected to VCC. The digital output is connected to IN0. To be isolated, the jumper between VCC and VDD must be removed. Assuming the relay board is rated for 24V, your 24V power would connect to VDD and your 24V ground would connect at the ground symbol.

When the digital output is in the '1' state, outputting 5V, there is no current flow through the LED in U1. When in the '0' state, the pin is at ground and can 'sink' 40 mA. Resistor R1 in series with the LED limits the current. With current flowing through the LED, the photo transistor is switched on and conducts. This switches on Q1 and enough current flows through the relay coil to energize the relay.

Your stepper motor controller may already have opto-isolation, as my relay board has.

Re: OptoIsolation of stepper motor drivers

Posted: Fri Mar 15, 2019 6:51 am
by Phaedrus
Thanks GurneyHalleck,
Actually I was asking about opto-isolation between the Arduino and the Stepper Drivers.There are two grounds,separate for VMOT and Vdd,so I was wondering if opto-isolation would be useful. But so far the board I am using is working fine,with both the grounds shorted,so I am leaving it as it is for the time.
Thanks again for your reply!

Re: OptoIsolation of stepper motor drivers

Posted: Fri Mar 15, 2019 1:33 pm
by GurneyHalleck
Glad to help. Actually a question I can answer.

Didn't know the details of your circuits, but I figured my relay board was a similar. Your stepper driver circuit would replace the stuff connected on pins 3 and 4 of U1.

I'm sure too, that you didn't need my walk-through, but I figured for everyone who knows what opto-isolation is, there are 10 who have no clue.