Close

Rev 1 VGA Resistors

A project log for ESP32 VGA PS/2

ESP32 runs FabGL to produce VGA display

land-boards.comland-boards.com 02/17/2020 at 15:440 Comments

I have the Hi/Low resistors swapped on the Rev 1 card. Easily reworked.

Updated Parts List

Consequence is the dimmed video is not as dim as it should be on the ANSI terminal header.

[Update] I dug a little deeper. Looks like the FabGL has contradictions in their web pages. One page seems to have the order different from the other. I was using the one page to define the pins when I did the above update. I think the original schematic was actually correct. Switching back.

The TerminalCharSet sketch shows this behavior well. When I swapped the resistors the screen got really dim. Switching the r0/r1, etc in the sketch initializer fixed the problem. I am going to switch back the parts on the card to the original order.

VGA Output Levels

Some pages say VGA output is 0.7V pp. This seems to be based on the composite video spec. Assuming that VGA inputs are AC coupled that could make sense. Composite video (IIRC) has a swing down to -0.3V for the sync. Black is 0V. The white level is 0.7V.

This makes me conclude that the original 400/800 ohm values are correct. Standard (5%) values are 390 and 810 ohms.

Discussions