Light Pens

[Zac67]

A light pen is little more than a photo transistor with a lens plus a button. I think the ones for the C64 work an the Amiga, too.

[Zac67]

bloodline wrote:
Lightpens only work on CRTs...

Good point, forgot about that.
Scandoubled VGA output may also be a bit of a problem, anywhere from reduced accuracy to no reasonable function at all.

Edit: here's an Atari project which would surely work on an Amiga, too: http://www.atariarchives.org/ecp/chapter_6.php

[Zac67]

Were lightpens ever actually good for anything, or just a silly gimmick?

Pretty cool actually, esp. on the Amiga (on the 64 accuracy was rather limited by HF output). The only thing I was missing was a horizontal table monitor since it's very tedious holding up your hand all the time.

[Zac67]

Pretty simple once you realize that the video output isn't just there but is built up line by line, from left to right. If you slow down time quite a bit then you can imagine the advancing electron beam hitting the phosphor right behind were the light pen currently points at. The phototransistor sends a pulse back to the video chip (Denise) which actually knows where it's currently at and just freezes the current horizontal and vertical counters to the lightpen register. :-D

[Zac67]

Hmm - I do remember using it on a friend's Amiga as mouse substitute with some kind of driver. I've got no idea if I had that driver, but I can't find it anyway. May have been the one in Aminet.