Multi-answer reply

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> How about using an EPROM, a DAC and a mixer?
> Basically, you have a counter that drives the EPROM, reset
> on every vsync, started on a Hsync and reset after 56uS (or
> whatever). The output of the EPROM is fed through a resistor-
> ladder DAC

I think that's pretty much how it could be. The shapes can of
course be in the micro's memory. It's going to be there for
timing anyway

It's similar to the way those message wands work. A tilt switch
is the "synch" and a clock puts the EPROM's or RAM's data
onto a LED-driving buss

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> > It'll be around 1" square in the bottom right corner

> Independent on the total screen size ? Or maybe rather a
> fixed % of the high/width of the screen ?

Fixed %. 1" was just an estimate for an average screen, say
23". It's actually probably a little more than that

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> If you don't have a precise lock, your logo will 'swim' or jitter as
> the uP clock beats against the video line rate. If your video is
> coming from a tape source, the problem is compounded by
> mechanical jitter unless it's time base corrected

Understood. Then wouldn't that also be true for the original video ?
So the graphic I want to add would jitter as much as the pixels on
any scan line. Given that the spec I looked up shows some tolerance
for synch pulses, how would I know when there's been mechanical
jitter, and what could I do (if anything is really needed to be done) to
correct that ?

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