The composite sync I need would come out of pin 1.
The composite video would go through a 0.1μF capacitor and then into pin 2.
pin 4 would be grounded.
pin 6 would be grounded with a 0.1μF capacitor and a 680kΩ resistor in parallel.
pin 8 would be connected to +5v.
Seems doable if that is all correct.
And if I wanted to get composite sync from hsync and vsync, how would I do that?
edit: I found this, which might actually be what I'm after:
This way I can get the composite sync from the VGA signal, rather than having to put an LM1881 chip inside the VGA box. This would be good because I'm going to be connecting a PC as well.http://www.tkk.fi/Misc/Electronics/circuits/vga2rgbs.html wrote:Analogue composite sync signal converter
First circuit is for connecting VGA card to video projector or a monitor which accept VGA card frequencies and has RGB + Composite sync input (1 Vpp signal level, 75 ohm input impedance).
This picture is available in GIF and Postscript versions.
Note: The circuit diagram does not show the wire giving power to IC1. The +5V power is connected to pin 14 and ground is connected to pin 7.
This circuit has been succesfully used with Electrohome Projection Systems ECP 4100 video projector in many VGA and SuperVGA modes. The circuit have been also used succesfully with one old Barco video projector using my VGA to TV drivers to get the VGA card to generate suitable signal frequencies which that old video projector can handle.
Component list
C1 22 uF 10V electrolytic
C2 22 uF 10V electrolytic
R1 2.2 kohm
R2 2.2 kohm
R3 1.8 kohm
R4 1.8 kohm
R5 2.7 kohm
R6..R8 47 ohm
U1 74LS86 or 74HCT86
T1 BC 547
T2 BC 547
another edit:
This page suggests that I can simply tie the hsync and vsync lines together to get csync on the Dreamcast with a VGA box.
I'll try this and report back how that works, and if that method works, perhaps it will work with an Nvidia card on the PC as well.Its possible to hack a Dreamcast VGA Box to output at 15khz ... If you are using a Jamma connector (which only has a connection for composite sync), then twist the Hor and Vert sync lines together and connect it to the composite sync on the Jamma connector.