jean@maxwell.Concordia.CA ( JEAN GOULET | DCKS004 | | ) (04/18/89)
Hello. I've been looking into making a light pen for my computer, and I think
the design is complete, except for one important detail. My circuit needs
to be restarted every time the electron beam starts a new horizontal line, so
I figure the HSYNC signal is what I need. Unfortunately I don't have the
schematics for my computer, so I'm wondering if someone knows if this signal
is availble on the 130XE motherboard. I looked at the schematic for the
400/800, but it looks like color, brightness, and timing info are mixed
together inside one of the chips and sent out as the video signal.
Would it be easier to extract HSYNC from the RF plug (or the composite output?
Or the luminance output?). If so, what kind of circuit would I need
(comparator, etc.)?
By the way, I realize the computer has hardware for decoding the position of
the light pen, but my experiments have shown that the x-input is so inaccurate
that it's unusable. My circuit will have a resolution of 640 on the x-axis
(overdesign is better than underdesign). I'll use the y-coordinate output
from the computer, though.
Jean Goulet
Electrical Engineering
Class of '89
Concordia University
Montreal, Canadahans@umd5.umd.edu (Hans Breitenlohner) (04/29/89)
In article <773@sunkisd.CS.Concordia.CA> jean@maxwell.Concordia.Ca ( JEAN GOULET | DCKS004 | | ) writes: >Hello. I've been looking into making a light pen for my computer, and I think >the design is complete, except for one important detail. My circuit needs >to be restarted every time the electron beam starts a new horizontal line, so >I figure the HSYNC signal is what I need. Unfortunately I don't have the >... The sync signal appears on pin 25 of the GTIA chip. I believe it is combined horizontal and vertical sync, scope it if you need to know for sure. From there it goes through a CD4050 into a summing network.