<Could cut some canned trannys open that is touchy to light and fill They all are! 2n5777 is a good photodarlington I've used a few. <those sensors from dead mouses, you can use either IR LED or strong <light. (YES! those light bulbs generate lot of IR). At lower than optimum voltage the IR is very there! IR however penetrates some paper tapes real well (if oil soaked better than white light!). It's been years since I've built one but I could reproduce it in an afternoon or two if need be. Allison