I have a Sanyo XP21 and want to control the up/down function of a Stewart screen. Since the XP21 does not have a 12 volt trigger output, what are my options? I believe there are current sensing devices that could do the 12 volt trigger; anyone have experience/recommendations with these? Do they/should they affect picture quality (some people feel that ANYTHING else on the line degrades the signal). Are there other possibilities?