tim@mcrware.UUCP (Tim Harris) (08/22/89)
Has anyone out there seen any plans for a homebrew Genlock device. To me it seems like the simpler Genlocks like the MiniGen can not be that difficult to make, I suppose timing would be the major issue that could cause trouble. Tim Harris
stevel@tybalt.caltech.edu (Steve Ludtke) (08/23/89)
In article <1326@mcrware.UUCP> tim@mcrware.UUCP (Tim Harris) writes: > > Has anyone out there seen any plans for a homebrew Genlock device. >To me it seems like the simpler Genlocks like the MiniGen can not be >that difficult to make, I suppose timing would be the major issue that >could cause trouble. > I worked on one of these in my spare time for about two months once. Let me point out that I knew almost nothing about phase locked loops when I started. I know quite a bit more now. The first issue that needs to be dealt with is horizontal and vertical sync. The RGB port has a horiz and a vert sync output line. These lines double as inputs in genlock mode. When the system boots up it checks these lines for proper horiz/vert timing signals. If they are present, it uses them as inputs otherwise it generates its own. Ok, now all you have to do is seperate the sync pulses from your external video signal. I spent a lot of time looking at various schemes for this (I have schematics for at least 5 devices that have a sync seperator in them. Every one does it differently.) and eventually came up with something that would work, but not well. This problem has been solved now, however. Nat. Semi. came out with an 8 pin ic, the LM1881, about 6 mo. ago. This chip seperates sync signals from even bad video signals with only 2 or 3 external components. Anyway, you should be able to use this directly with the h/v inputs on the Amiga. Now on to the harder problems. H/V sync will allow you to overlay video, but very poorly and without color. To get a solid overlay with color, you have to sync the amiga clock with the colorburst in the video signal. This means you have to take a 3.579 MHZ signal and generate a 28.63 MHZ clock from it. To do this you need some sort of PLL. I put one together using a NE564, but despite days of work, I could never get it to lock on to 28 MHZ. Despite my center freq setting, it insisted on remaining unlocked or locking on to 14 MHZ. If anyone tries this and gets it to work I love to see the circuit. If you can get this working, you're at least half way there. Oh yeah, I forgot, you also have to get the colorburst signal out of the ext. video signal. I also spent a while on this, and my failure to get it working to my satisfaction is also probably why the PLL circuit wouldn't work correctly. In any case, I haven't tried it, but the LM1881 also has a burst output that (with some sort of switching) should allow you to pull the colorburst off of the video signal quite easily. Hmm, maybe I'll even give this a try now that I thought of it. The next thing to deal with is switching. The amiga has a handy output that switches when the color displayed is 0 (background). Hooking this up to a 4051 CMOS analog switch will do the switching pretty well. That's it, unless you want RGB output as well (or own a A500 with no color composite out to mix with the ext. video source). For that, you'll have to get an NSTC->RGB chip. I've never tried this, but I've seen enough postings about it to know it's not an entirely trivial task. Then, of course, for 500 owners, you'll need an RGB->NSTC converter too. Anyway, as you can see, it's not a trivial project. I eventually gave up (because of the PLL and color problems) and bought a closeout Commodore genlock for $99. If anyone goes anywhere with this, however, I worked on it long enough that I'd still be interested in seeing the plans. --------------------------------------------------------------------------- Steve Ludtke stevel@tybalt.caltech.edu ..!cit-vax!tybalt.caltech.edu!stevel stevel@citiago (Bitnet) 72335,1537 (Compuserve) I DO ...
hue@netcom.UUCP (Jonathan Hue) (08/24/89)
In article <11695@cit-vax.Caltech.Edu>, stevel@tybalt.caltech.edu (Steve Ludtke) writes: > In article <1326@mcrware.UUCP> tim@mcrware.UUCP (Tim Harris) writes: > > > > Has anyone out there seen any plans for a homebrew Genlock device. > I worked on one of these in my spare time for about two months once. Let me How about using a Motorola MC1378 (Color Television Composite Video Overlay Synchronizer)? This alone won't do it, but it looks like you just need to generate a couple other timing signals to get this thing to work. It's in the Motorola Linear and Interface Integrated Circuits data book. -Jonathan
charles@hpcvca.CV.HP.COM (Charles Brown) (08/24/89)
> This means you have to take a 3.579 MHZ signal and generate a 28.63 > MHZ clock from it. To do this you need some sort of PLL. I put one > together using a NE564, but despite days of work, I could never get it > to lock on to 28 MHZ. Despite my center freq setting, it insisted on > remaining unlocked or locking on to 14 MHZ. > Steve Ludtke It is hard to tell from your description, but it looks like you were not using the best design for a frequency muliplier. -------------- ------- 3.579MHz >-| | | | | phase/freq | | VCO | | difference |-->| |---o------------------> 3.579MHz * N -->| | | | | | -------------- ------- | ---------- | | | | | --->| divide |--- | | by N | | | | | | | ---------- | | | ----------------------------------------------- For N=8, the output frequency will be 28.63MHz. The VCO should be centered on 28MHz with a narrow capture range if you can arrange it. The phase/freq block should have a good low pass filter for stability. The divider is a simple digital divider consisting of three flip-flops. A ripple divider will do. -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer. "The guy sure looks like plant food to me." Little Shop of Horrors
king@dciem.dciem.dnd.ca (Stephen King) (08/25/89)
In article <2190@netcom.UUCP> hue@netcom.UUCP (Jonathan Hue) writes: >How about using a Motorola MC1378 (Color Television Composite Video Overlay >Synchronizer)? This alone won't do it, but it looks like you just need to >generate a couple other timing signals to get this thing to work. It's in the >Motorola Linear and Interface Integrated Circuits data book. One problem you may have with this is getting a 28MHz clock (8x SC) for the Amiga from the 38MHz (10x SC) output of the the MC1378. I designed & built a system a few years ago (68000, 512k) which used the 1378 to overlay bit-mapped graphics onto a video signal. My system used a 14MHz (4x SC) clock which was derived from the 38MHz using a single PAL. This gave an unsymmetrical clock signal; my system didn't mind, but I don't know if the Amiga could handle it. Apart from this, there may be difficulty in obtaining some of the circuit components (200nS delay line, chroma bandpass transformer) - I got a local distributor to give me some 'samples'. There is a Motorola application note which includes a PCB layout for the 1378. Best of all, it works!! 2 chips + assorted passive components = genlock. -- Se non e` vero, e` ben trovato ...{utzoo|mnetor}!dciem!dretor!king king@dretor.dciem.dnd.ca
lee@sed170.HAC.COM (John Lee) (08/26/89)
In article <11695@cit-vax.Caltech.Edu> stevel@tybalt.caltech.edu.UUCP (Steve Ludtke) writes: [...good discussion of sync derivation problems deleted...] > The next thing to deal with is switching. The amiga has a handy >output that switches when the color displayed is 0 (background). Hooking this >up to a 4051 CMOS analog switch will do the switching pretty well. [...] >--------------------------------------------------------------------------- >Steve Ludtke >stevel@tybalt.caltech.edu ..!cit-vax!tybalt.caltech.edu!stevel >stevel@citiago (Bitnet) >72335,1537 (Compuserve) I DO ... Hmmm. I don't have my databook with me at the office (I'm a software engineer, even though my diploma says EECS) but isn't the bandwidth on the 4051 too low (~1MHz) for a video signal (>3Mhz)? Or is that the (4021 | 4031, I forget)? Other than that, assuming you can work out the cross-talk/noise problems, it seems quite possible to build one as simply as you describe. Why don't you give it a shot with the National chip and tell us about it? ------------------------------------------------------------------------------- Raining CATS and DOGS? Join the RATS: Remote Amiga Teleconferencing System +--------+ John Lee | HUGHES | +--------+ ARPAnet: jhlee@hac2arpa.hac.com Hughes Aircraft Company The above opinions are those of the user and not of those of this machine.
grau375@watcsc.waterloo.edu (Michael Grau) (08/26/89)
> article from Steve Ludke ....deleted
Besides the info already given from Steve, is there anyone that can give
more information on making your own genlock? What about part numbers,
pin outs, diagrams, and also line descriptions of the connector from
the Amiga? Myself and a couple others are interested in this idea. We
would appreciate any help.
Thanks in advance.... MikeClassic_-_Concepts@cup.portal.com (10/31/89)
I have one of the original (ugh, there was nothing else available at the
time) Commodore genlocks. I spoke with an engineer at a technical institute
where they also use one on an Amiga 1000 and he said he made some adjustments
to theirs which improved the output signal. He was not willing, however, to
divulge what he had done to tweak it.
Has anyone else made improvements to a Commodore Genlock that they are
willing to share? I'm pretty good with components and a soldering gun, but
lack a scope and knowledge of adjustments to video signals. Julie