Hello. Maybe I haven't exactly described the video source. It is really the problem of Gain Control. I have _extrenal_ multiplexr ( and chip has it's own too - internal ) so I have: cameras: 1: --- | 2: --- |M ---- [TV input of chip ] --- .. --- |U 8: --- |X So i receive only one frame at the moment. When chip detects blank frame it increases brightness ( not at the moment, it lasts some frames ). So it is really AGC. Regards, Dmitry. P> On Thu, 13 Sep 2001, Dmitry Alexeyev wrote: >> Hello. >> >> I have BT878 card and external multiplexer with several monochrome cameras >> connected to it. If one camera is off ( blank screen ), bt878 >> automaticaly increases brightness, so I can see nothing on frames from >> other cameras. >> How can i turn off AGC ? >> >> Dmitry >> P> Seems your problem is the multiplexer not the AGC. P> If properly clamped to black level AGC will probably P> no longer interfere. P> This of course requires minimum expertise to P> clamp the multiplexer input to black level P> when camera is off (using a capacitor, resistor P> or combination, after analysing the input circuit). P> However, if you have such ability it must be P> pretty simple and "safe" once it's just a simple P> clamping. (clamping activation via camera power) P> But with today VLSI "closed source" trend things P> simple like this may even be impossible. :-( P> Open source hardware too will be great.... P> schematics, information access... or better P> put the closed hard crap in trash together P> with the closed source soft too. ;) P> No need to mess the AGC that seems to be not P> the cause but just the symptom of a floating P> input signal. P> Hope this helps. P> -- P> HOM: http://www.momentus.com.br/users/hook/ P> GPG: http://www.momentus.com.br/users/hook/GPG-PauloCastro.asc
