77 Circuit for Converting from VGA to Fixed-Freq. RGB
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
77 Circuit for Converting from VGA to Fixed-Freq. RGB
More information and additional circuits are available on the PC Video FAQ WWW Site. They have not been included here for brevity and because some of the information is presented in a graphical manner. Please refer to http://www.heartlab.rri.uwo.ca/vidfaq/fixed.frequency.html for more information and superior circuits for driving workstation monitors.
The following is an ASCII file of a circuit which combines the vertical and horizontal sync signals from a VGA card to output a composite sync signal compatible with many fixed frequency monitors. If necessary, the Csync line can be connected with the green video line to produce a sync-on-green signal. This circuit produces a signal that is compatible with many fixed-frequency monitors, but ensure that the signal you are sending has the same vertical and horizontal frequencies as the monitor expects.
For more information on how others have done this, read pertinent parts of this FAQ and refer to: http://rugmd0.chem.rug.nl/~everdij/hitachi.html - Experiences hooking up a Hitachi monitor http://www.midcoast.com/jp/sun/ - More experiences with a Hitachi http://www.devo.com/video - Fixed Frequency PC Video FAQ
*** USE AT YOUR OWN RISK - Others have used this circuit but I have not!
[From: Roger Wolff (R.E.Wolff@et.tudelft.nl)]
VGA connector monitor
R ----------------------------------------------------- R
gnd ----------------------------------------------------- gnd G ----------------------------------------------------- G
gnd ----------------------------------------------------- gnd
B ----------------------------------------------------- B
gnd ----------------------------------------------------- gnd
___________
| |
| 74HCT86 |
| |
| |
hsync -----------|1 |
| 3|----------------------------- Csync
vsync -----------|2 |
| |
| |
| |
gnd--+--|7 14|--+-- +5V
| |___________| |
| |
|________||_______|
||
0.1 uF
Use COAX cables for the "data" (R, G, B) lines. You can use just about anything for the hsync and the vscyn lines but keep them as short as possible. Around 30 cm (a foot) is fine. I use a COAX cable for the Csync line too, as I need a BNC connector at the end of the monitor anyway. I didn't do anything about termination, and all seems to be A-OK.
I gather the power for the 'HCT86 from inside the computer. You can find something yourself (find a 5V powerline going to the leds or something), or use something that resembles those "add-on" fans. The latter usually use 12V, but they show the principle: a male and a female cable connector and 6 wires should do the trick.
This worked for my Grayscale monitor (where the R and B lines are not needed), and now works just fine for my 21" monochrome monitor.
I start X at boot-time, before ANYTHING runs: my Xserver owns PID 3. I then quickly bring up the network and start an Xconsole. This allows me to follow the rest of the bootsequence.
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