INDI supports a few different types of relay controls for external shutter release.

DSUSB is a special device made by Shoestring Astronomy. In the Nikon INDI control panel, you would just set the port to "dsusb" and it will look for that special device plugged into a USB port. If it finds it, all is good in the world, and it should "just work".

The KMTronic relay boards present themselves to the system as a USB-to-serial adapter, and it listens for special commands to open and close the relay.

If you put anything other than "dsusb" into the port field in the INDI control panel, it will assume it is a serial port (such as /dev/ttyUSB0) and will attempt to open it as such. If it's a Nikon camera, it will send the special KMTronic commands over the serial port to open or close the shutter. It will also toggle the RTS line on the serial port to open and close the shutter. So if you attach a USB-to-serial adapter that isn't a KMTronic relay board, you would have to wire up a relay to the serial port's RTS line to control the shutter.

If you have some type of relay control board that expects commands over the serial port, and those commands aren't the same ones that KMTronic uses, it probably won't be usable with INDI.

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