On Sat, 12 May 2001, Thomas Hargrove wrote: > Well, incase anyone is interested, I have been working on a way to get > composite out on cheap bt848 based cards. I found the correct pin on the > tuner, and connected a rca cable to it and to a ground. Sounds like fun! > (BTW: I got the specs from someone on this list. They are here: > ftp://telepresence.dmem.strath.ac.uk/pub/bt848/spec) > > Right now, I have a good signal except for one thing. I get a faint light > bar that moves slowly up the screen. Other than that, there is no noise. If your video is NTSC and your AC power is 60 Hz, this sounds exactly like what 60Hz hum beating against the 59.94Hz vertical scan rate looks like. I'd verify that by looking at your new video output with an osciloscope. First, make sure that your composite video monitor's grounded power cord is connected to the same power strip as the computer. Then consider where you're connecting the new connector's "ground" on the board, and try moving the connection. If the board seperates analog and digital ground, use analog ground. In this cas AGND and DGND will be connected together somewhere on the board, but otherwise they need to be kept seperate. The Bt879 datasheet says that it is possible to build boards either way. Keeping analog video signals clean in the high-speed digital environment of a PCI card can be tricky. > I was wondering it this is interference with the capture chipset and my TV. > I think I might disconnect the pin from the board, but that will pernanitely > damage the card. Can anyone tell me if that might solve my problem? Hmmm, probably not. Maybe it would be easier to temporarily break the connection somewhere nearer to the tuner? I'm am a bit surprised that you can connect another video load in parallel with the capture chip and get decent video without a buffer of some kind. You are probably double-terminating the tuner output; there should be a 75-ohm termination resistor near the BT chip input, and the composite output adds a second one, probably cutting the video signal level in half and relying on the AGC circuits to fix things up. Anyway, I'm interested in corresponding on this and other analog video hacks. Just curious, what card are you using? I'm having no success making v4l/bttv work at all with a Hauppage "WinTV Go" card which is one of the cheaper cards available these days. Steve -- Steve Tell tell@xxxxxxxxxxxxxxx
