Guru
Joined: 05/10/2019
Location: United KingdomPosts: 2217
| Posted: 12:54pm 21 Jan 2022 |
It's still 75R to ground at the monitor end - or you have to assume that it is. The max current that still has a reasonable voltage (Voh>2V6) from a Pico pin is 12mA if it's been set that high. That doesn't give you much to play with at the active end. You should be able to drive a VGA input to 0.7V (or close to it) pretty easily over a normal length VGA lead though.
Don't be too fussy. If you sit far enough from the monitor to need an extra long cable then you can't read it anyway. :) Peter's original scheme works nicely in real life, in spite of a nasty glitch in the middle of the R-2R ramp caused by heavy loading on the output (tested in simulation, not on a scope). These things are not generally visible.