Run a stepper from 2 DM542 drive

[m_c]

I've not really been following this thread, but the simplest option is a 4PDT relay as has been suggested, but you only need to switch the Dir+/-, and Step +/- signals.
Driver is permanently enabled, so you don't have to worry about it losing power and the Z dropping.
And the GND is only needed for the main power, as the driver inputs are optoisolated.

The only issue with using a relay is with switching such a small current, the contacts will likely oxidise with use due to lack of current to wet/clean the contacts, eventually leading to lack of continuity,
For a circuit only switching occasionally, it'll likely be a long time before failure is likely to be an issue, but it's something to bear in mind.

[A_Camera]

I've not really been following this thread, but the simplest option is a 4PDT relay as has been suggested, but you only need to switch the Dir+/-, and Step +/- signals.
Driver is permanently enabled, so you don't have to worry about it losing power and the Z dropping.

That is only true if he ALWAYS wants to have the stepper energised and always holding. That is not always desirable or even advised. So unless you absolutely certain that he doesn't care about enabling/disabling the driver it is indeed necessary to switch the enable signal also. Regardless of which, there is no harm in switching it, but there can be harm in not switching it.

And the GND is only needed for the main power, as the driver inputs are optoisolated.

GND is the same as STEP - , DIR - and EN -. It is better to connect those to the same - output as the one providing the control signals. Again, it would do no harm and we know too little about his design and implementation.

The only issue with using a relay is with switching such a small current, the contacts will likely oxidise with use due to lack of current to wet/clean the contacts, eventually leading to lack of continuity,
For a circuit only switching occasionally, it'll likely be a long time before failure is likely to be an issue, but it's something to bear in mind.

That's why I said that a small signal relay needs to be used, not a contactor. You talk about a contactor which is designed for high voltage and current.

[m_c]

That is only true if he ALWAYS wants to have the stepper energised and always holding. That is not always desirable or even advised. So unless you absolutely certain that he doesn't care about enabling/disabling the driver it is indeed necessary to switch the enable signal also. Regardless of which, there is no harm in switching it, but there can be harm in not switching it.

If you'd looked at the relevant photo, you would see the Enable on the driver has nothing connected to it, plus there is also the post stating he doesn't want the axis to become disabled to avoid the axis dropping, so connecting the enable is not needed.

GND is the same as STEP - , DIR - and EN -. It is better to connect those to the same - output as the one providing the control signals. Again, it would do no harm and we know too little about his design and implementation.

Not on the existing step source, as again, the photo shows differential outputs.
However I did think about this earlier, as the alternative controller may not have differential outputs, so some thought may be needed in that regard.

That's why I said that a small signal relay needs to be used, not a contactor. You talk about a contactor which is designed for high voltage and current.

All relays, apart from specialist relays have minimum switching currents. It is not something that only applies to contactors.
Good relay manufacturer's will publish the relevant detail in the datasheet.

[BeagleBrainz]

Yeah so basically go for a relay rather than a contactor.

[BeagleBrainz]

Or if you want to be really simple, a 4PDT switch. Which would mean a human having to do the change over. Would do even during just testing.

[A_Camera]

Or if you want to be really simple, a 4PDT switch. Which would mean a human having to do the change over. Would do even during just testing.

...but that is really difficult to find. Of course, it could be done with 2 or even 4 individual switches also.

[BeagleBrainz]

I wouldn't assume -DIR or -STEP are connected to ground, the output circuit could be a NPN transistor (open collector). So the safest bet would be to put each (for lack of better description signal) on a separate pole.
Maybe the output circuit of one of the boards can recognize an open circuit, on either the STEP or DIR causing a fault condition.
The user has provided no circuit diagrams so it is really hard to say which way to jump.

It would be the same as asking a programmer to design a routine to process a data packet without actually telling them anything about the format of the data packet.

[A_Camera]

The user has provided no circuit diagrams so it is really hard to say which way to jump.

Yes, that's the key issue. We are all only guessing. I provided my solution, but yes, other solutions might be needed, we have no idea since we don't have enough information about his design. I was however very clear that the solution I proposed is what I use and it works for me, and I bet you that I could make it work with his driver also.

There are two documented possible ways of connecting the driver, in one case you bridge all the + to the same and switch all the - signals, the other way is what I am using, which is I think the most commonly used. Basically there is very little difference between them (I know that electrically the difference is huge), and both uses the same principle, but without knowing all the details of his solution it is impossible the say which is right and which is wrong.

[A_Camera]

The user has provided no circuit diagrams so it is really hard to say which way to jump.

Yes, that's the key issue. We are all only guessing. I provided my solution, but yes, other solutions might be needed, we have no idea since we don't have enough information about his design. I was however very clear that the solution I proposed is what I use and it works for me, and I bet you that I could make it work with his driver also.

There are two documented possible ways of connecting the driver, in one case you bridge all the + to the same and switch all the - signals, the other way is what I am using, which is I think the most commonly used. Basically there is very little difference between them (I know that electrically the difference is huge), and both uses the same principle, but without knowing all the details of his solution it is impossible the say which is right and which is wrong.

[gabi68]

Well, taking your advices I have a relay with appropriate socket on the way
https://www.rapidonline.com/Relpol-R...-Relay-61-6063
and I will connect Pul-, Pul+,Dir- and Dir+ and power the relay from a 12V power supply.

I also bought this fancy button
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1 .

The last advice need it is where should I connect the button to make the change of the inputs?

Thank you
Gabi