Yes, the 24V side will be powered by an auxiliary 24V power supply. It's just that it looks quite simple, I was expecting a far more complicate solution

Hi,
As I mentioned before, it is quite simply in theory.
That link to the SS Relays didn't work for me but looking at some of the products on that web site, they could work. I see they have special configuration relays that can run to 100 kHz which is probably more than you need.
It appears that the standard relays are rather slow and this may cause problems but I also think this approach may be just as simple or complicated (depending on point of view) as using a buffer chip. The only thing you save with the relays is the pullup resistors/

The more I think about this the more I think my original suggestion of the SN7407N type chip would work as well or better and be a lot cheaper: ($1.00) for the chip that can handle step and dir for 3 axis, 2 pullup resistors per axis, and a couple of inexpensive capacitors on the 24V power supply.
I'd also recommend isolating the PP from the 24V with more than just the 7407 or the relays and would use HCPL2531 optocouplers These are very fast and are only $2 each with one per axis .

I did not think it through carefully but I also believe the CS Labs Universal Converter (the 63 Euro one - differential TTL to OC) could handle everything if configured as an open collector output. Not inexpensive but almost a complete solution rather than a bunch of parts.

Graham

GBowes: here is a shorter version of the URL that TPS posted
http://bit.ly/1sx9sXo

(the long one seems to have been altered by the forum)

Thanks. That relay would be great solution except for one slight problem. It has the isolation and buffers the signal and converts to 24V. All you would need is the 24V supply and a couple of capacitors, You would need two relays for each axis (step + dir).

I had guessed that it might be a little expensive, but I was wrong.
Mouser wants $92 each so $560 for the 6 needed for three axis.

That makes the CS Labs unit look cheap at about $80 plus shipping.

Graham