[wasyoungonce (Brendan)]

Hi Alex, I can help, I'm in Melbourne and have to skills to really bugger this up (Just kidding).

I have to ask why are the interfaces for ST4 using relays? Relays are terribly laggy devices..aka they take time to build coil current and respond to a signal and same when de-energising due to back emf coil current? Is this some legacy or am I missing something?

I think it would be better using an opto Isolator like the 4N25 or 4N28 or even a quad device in the one dil package. See my pic.

In this...when a command is sent to the ST4 jack, the led diode produces a pulse which turns on the transistor making it effectively short cct. The opto transistor is across the handset switch thus...viola a signal is passes like pressing the switch.

Of course a device like all these is and can only give approximations of ST4 commands depending upon how low you can set your guide speed...aka to 1X sidereal.

Anyway see what you think and get back to me.

Brendan

edit:
I forgot ..No charge...only the parts costs (in reply to your thread in the wanted forum)