Cardco was started in 1982 by Ed Lippert and Breck Ricketts out of a garage in Kansas with four employees. Breck designed almost all of the products and Ed was the energetic salesman. The company grew too quickly and lacked necessary maturity. For example, on Tuesday, February 19, 1985, a U.S. federal trademark registration was filed for Cardco by Breck. The USPTO had given the Cardco trademark serial number of 73522548. By November the federal status of this trademark filing was ABANDONED-FAILURE TO RESPOND OR LATE RESPONSE. The business collapsed by 1989. Manufacturing rights were sold off and the founders went on to pursue other business ventures. More information can be found here: http://www.pcmuseum.ca/companyprofile.asp?id=50
A light pen is a pen-shaped input device which connects to a compatible computer (such as the VIC-20). The device contains a light sensor which, when pointed at a cathode ray tube screen, generates a signal each time the electron beam raster passes by the spot the pen is pointing at. The VIC chip accepts this signal, generates the X and Y coordinates in a pair of registers, and, if desired, causes an interrupt to the CPU every time new coordinates are reported. It is difficult to find a light pen that still works today. Plus, you need an old TV with a picture tube (not an LCD). The first light pen was called a "light gun" and in 1952 it was part of the Whirlwind Project at MIT. Subsequent devices were used to hone in on suspicious blips on the CRT in the U.S. air defense system (research the Whirlwind and SAGE systems). The light pen became moderately popular during the early 1980s. Since the current version of the game show Jeopardy! began in 1984, contestants have used a light pen to write down their wagers and responses for the Final Jeopardy! round.
Despite the ease and availability of this technology, it was rarely used, owing mainly to lack of precision. First of all, the X coordinate is "rounded off" to even pixels (or more precisely; the reported X coordinate is an integer representing half of the actual horizontal position). Second, problems with noise, non-ohmic properties of the involved cables etc. causes a lot of "jitter" (several pixels) on the reported X coordinate, even if the pen is held completely still over a specific point on the screen. The light pen also requires the entire screen image to be quite bright, to ensure a significant "spike" in the amount of light received as the beam passes by the pen's tip. Any dark graphics causes the aiming point to "slip off" the dark areas, catching a nearby brighter spot on the screen instead. These limitation make the light pen system unsuitable for "precision work", such as drawing things or pointing to menus on the screen, leaving only "non-precision" shooting games as a target application for this technology.
You can right-click the document on the left or download the full instruction manual and demo disk. To the best of my knowledge this manual/disk is not available anywhere else online today, so it has also been sent to http://www.bombjack.org/commodore for safe keeping. In addition to this light pen, I also have a page to discuss the Cardco numeric keypad and 6-slot expansion unit.