My two cents...
I also used the book referenced in the link posted earlier to build my lightpen. You do need the 7400 in between the TIL414 and the port, as it's acting as a "debouncer". You can also substitute a 7414 Schmidt trigger chip, 74121/123 multivibrator, or a simple 555 one-shot to do this. I also highly recommend using as "flat" and dark a pen barrel as you can find. I found the Papermate Comfort-mate® black to do the trick nicely. This helps to prevent false triggers due to reflections from neighboring pixels.
The reasons my pen is sitting unused have been mentioned earlier:
1) Resolution. On the C64, I could only get it to one character (8x8 pixel block). This is why FlexiDraw pens were better - they added special lenses in the nose to allow single-pixel pointing, and they also had one of the smallest buttons, but with the advent of SMT components the buttons are no longer an issue. You may be able to play with some optical components to come up with a better solution (fiber optic couplers?)...
2) Circulation. Yeah, unless your monitor is mounted inside a desk with the screen facing up, then your arm is going to feel like a lead bar in about five minutes. This is why even FlexiDraw didn't sell too many of their excellent pens. Koala pads did much better (and Kurta, et. al.).
3) Software. GEOS and a couple of paint programs allowed for them, but not much else. I wound up using my pen to act as a light-activated tachometer. It worked up to about 20-30KHz, IIRC.
If all that doesn't deter you, then have at it - but I'd still recommend finding a good 1351 mouse.
banzai
