Jeff, I've scanned a couple of light pen circuits http://home.clear.net.nz/pages/joecolquitt/lightpen.html (I'd tend to trust ETI, had pretty good experience with their circuits) Both of these were most likely used with TVs rather than monitors -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body