Thanks Mike for the circuit. I assembled it and now it works in my TV. :) By the way, this is where I experiment with the SX video thing. The TV is assembled from a black-and-white monitor and a radio channel block from a TV. The block has a video output with a DC component of a few volts (about 2V - I didn't measure it), but the monitor works only for zero DC video signal. Before I used a 'dirtier' circuit of a 22 uF capacitor and an adjustable 470 Ohm resistor in parallel, connected between video ouput of the block and video input of the monitor to lower the DC offset. It sort of worked, with some of contrast lost. Now it's much better with the new circuit :) One catch with the DC separator is that the capacitor is charged by the transistor through the video output and the output has to have a sufficiently low impedance, which my radio channel hadn't. So I added a p-n-p emitter follower before the DC separator to make it work. It should also work for the SX comparator input (or simply a digital input) if the transistor base is adjusted to something like 0.7V. I'll check it. Yesterday I tried a circuit that separates sync signal from video. It uses 2 transistors and a few resistors and capacitors. It has a good digital output, but I still can't make SX synchronize at the same period to every individual HSYNC pulse in the noise presence. So besides sync separation a PLL scheme should be added. In that case, I guess the sync separation can be made in software altogether, if the DC separator and a comparator is used. Thanks all for replies, Nikolai ---- Original Message ---- From: Michael Rigby-Jones Sent: Friday, December 08, 2000 10:29:13 To: PICLIST@MITVMA.MIT.EDU Subj: [sx]: SCENIX VIDEO VIRTUAL PERIPHERAL Design Challenge and Co ntest >> -----Original Message----- >> From: Nikolai Golovchenko [SMTP:golovchenko@MAIL.RU] >> Sent: Friday, December 08, 2000 7:30 AM >> To: PICLIST@MITVMA.MIT.EDU >> Subject: Re: [sx]: SCENIX VIDEO VIRTUAL PERIPHERAL Design Challenge >> and Contest >> >> James Newton wrote: >> > I've been thinking about sync detect without using an external sync >> > separator. Doesn't seem to be much on the web about doing that with a >> > microcontroller... >> >> > ...but it also seems to me like it ought to be very possible. >> >> Sync detection is sure possible with a SX. I made a quick >> test on the evaluation board (50 MHz SX28), just for >> horizontal sync, using the comparator to catch the sync >> pulses. It works in most cases, but sometimes, when video is >> bad quality (noisy, but screen is stable) lines are missed >> with that setup. >> >> There are a few problems: >> >> 1) Comparator lowest input voltage level is 0.4V. With a 0 >> to 1V video, sync threshold is at about 0.15V. So it is out of >> specs, though seems to be working. >> > Have you DC restored the composite video? If not you will see this problem > as the video content changes. I have attached a very nasty ascii circuit > that shows a cheap and easy method of acheiving this. Credits for this go > to a Mike Day who published the Dirt Cheap Frame Grabber that used this > circuit. >> 2) Noise. I wonder how screen remains stable even when >> signal is noisy. There must be some filtering in a TV. I'll >> try to dig the sync separator circuit from an old TV. >> > ISTR that TV's use a "Flywheel" circuit, which is actualy a phase locked > loop. This would give a good degree of noise immunity. This could probably > be implemented with the scenix, although I'll leave that as an exercise for > the reader :o) > Regards > Mike >> <> -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics