PicoMite VGA check


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KD5ZXG
Regular Member

Joined: 21/01/2022
Location: United States
Posts: 53
Posted: 07:21am 21 Jan 2022      

1N4148 clipping diodes have lower dynamic resistance than matches 75 ohm cable.
It gives a good voltage, but maybe also standing waves and echos.

180 over 150 divider calculates better match to 75 w similar voltage at the far end.
270 for Green's MSB, 270 + 270 = 540 for Green's LSB, all together over 150.

I've calculated even closer values if you have a stash of E96 series.



Fair warning: I've only simulated, not yet tested these values.
My Pico won't output higher than 3V when driving an LED, which may not
be a safe assumption it would output the same when VGA DAC is the load.

I cut one end off an old VGA cable only to have trouble getting solder
to wet the ground braids. Aluminum or stainless I don't know? But it's
most annoying to have ruined a cable I now maybe can't use.
Edited 2022-01-21 17:44 by KD5ZXG