I'd like to let you know that I uploaded an article to the Technical section, under DIY Projects.
It is a peripheral controller for the Dragon that can control up to 4 devices and is a PCB that connects to the Dragon through the cartirdge connector.
It appeared on Issue 7/1993 of the spanish magazine "Electrónica Fácil" (Easy Electronics) and I though it would be of your interest.
I'll upload an english translation as soon as I can.
Best regards!