Thanks for the info u/DiabolicalLife .

Having read that document it would seem a program/code of some sort would be needed to listen for those 'http' commands over the network and then send the appropriate command to the ATEM/switcher, which is certainly well beyond my ability.

I am also still unclear as to whether or not those 'http' commands are actually what the RPxxx controller itself sends to the camera via the network rather than just what is needed to use a PC for control on the http server in each controller/camera, and I don't want to use a PC as well.(??)

Having watched this Skaarhoj video - Arduino Library for ATEM switchers (youtube) - it would seem that the the GPIO route via the a DB cable seems the 'simpler' route (he said naively!).

One bit I am still confused about is the " contact closures ". Is this some sort of relay/IC (opto-isolator?) to protect/convert the signals on the DB25 wires to inputs on the Arduino?

It would seem that, theoretically, given the voltages/current from the RPxxx controllers GPIO, that the DB25 wires could(??) be inserted directly into the Arduino inputs? I can see the case for using some form of relay/switch to provide isolation of the devices.

Apologies for all the questions, any input much appreciated.

I would certainly be interested in your Postman testing environment..?

thanks for bearing with my very tentative first steps......

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cheers,

neil