This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. ------_=_NextPart_000_01C060F0.F1CC75E0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C060F0.F1CC75E0" ------_=_NextPart_001_01C060F0.F1CC75E0 Content-Type: text/plain > -----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 > <> ------_=_NextPart_001_01C060F0.F1CC75E0 Content-Type: text/html Content-Transfer-Encoding: quoted-printable RE: [sx]: SCENIX VIDEO VIRTUAL PERIPHERAL Design Challenge and = Contest

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.


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

= <<dcrestor.txt>>

------_=_NextPart_001_01C060F0.F1CC75E0-- ------_=_NextPart_000_01C060F0.F1CC75E0 Content-Type: text/plain; name="dcrestor.txt" Content-Disposition: attachment; filename="dcrestor.txt" Cheap DC Restore for composite video +5v +------------+ | | \ | /4k7 | \ c| |_________b|/ | |\> 2N2222 V 1N4148 e| 1uF - |----||---0 Video In | |---------0 video Out | +----------------------0 Ground ------_=_NextPart_000_01C060F0.F1CC75E0-- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads