PLL frequency multiplier.
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Posted by Frank Buss on July 3, 2008, 11:17 pm
Please log in for more thread options NBTV sounds interesting. But according to this webpage http://www.nbtv.wyenet.co.uk/index1.htm (chapter "Club standard"), there is a sync every line. So I don't think that it would be a good idea to use a PLL for the pixel clock, but you should simply start scanning with each sync pulse. You can even increase or decrease the pixel clock to scale the image, like with old analog monitors. Or you can measure the average time between two syncs and calculate a counter delay for full screen fit, like the auto-adjust button on more modern monitors. A PLL could be useful for restoring missing line syncs with noisy signals. > Im going to be using an ATmel AVR, so if you know of a way to make a
> multiplier out of an AVR CPU. let me know. There are ATMega parts with hardware multipliers, but I think you won't need it for this project. Another nice page about NBTV: http://www.nbtv.wyenet.co.uk/conv04.htm But looks (and sounds) a bit like a coffee party for retired electronic engineers :-) Nevertheless I like the idea with the mirror. Reminds me to this video: http://youtube.com/watch?v=oLygWkHo9nw In this video you can see how such a globe could be built: http://youtube.com/watch?v=LYo0LOUK5Rs -- Frank Buss, fb@frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Martin Griffith on July 4, 2008, 7:25 am
Please log in for more thread options >Well timing has to be rather critical. its being used in a narrow band
Would something like the EL4584 from intersil be any use?
>video sync. so it has to be accurate. > >Well, see i play around with NBTV scanning disk television as a hobby. >I was going to make an NBTV emulator with a 32x48 LED matrix. > >since it is a 32 line resolution, at 12.5 frames per second, you have >a line sync of 400hz. > >the problem is theres 48 vertical resolution pixels per 1 line scan. >so that means i would have to multiply my 400hz pulse by 48 or 19.2khz >to scan the vertical LEDs to keep them in sync. > >Im going to be using an ATmel AVR, so if you know of a way to make a >multiplier out of an AVR CPU. let me know. > >Thanks! http://www.intersil.com/cda/deviceinfo/0,0,EL4584,0.html martin | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Mike on July 4, 2008, 7:41 am
Please log in for more thread options it would have worked, but its divisors are setup for NTSC and other systems.
it doesnt have a 48 divisor. > On Thu, 3 Jul 2008 17:12:52 -0700 (PDT), in sci.electronics.design
> >>Well timing has to be rather critical. its being used in a narrow band
>>video sync. so it has to be accurate. >> >>Well, see i play around with NBTV scanning disk television as a hobby. >>I was going to make an NBTV emulator with a 32x48 LED matrix. >> >>since it is a 32 line resolution, at 12.5 frames per second, you have >>a line sync of 400hz. >> >>the problem is theres 48 vertical resolution pixels per 1 line scan. >>so that means i would have to multiply my 400hz pulse by 48 or 19.2khz >>to scan the vertical LEDs to keep them in sync. >> >>Im going to be using an ATmel AVR, so if you know of a way to make a >>multiplier out of an AVR CPU. let me know. >> >>Thanks! > Would something like the EL4584 from intersil be any use?
> http://www.intersil.com/cda/deviceinfo/0,0,EL4584,0.html > > > martin | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Tim Wescott on July 4, 2008, 2:29 pm
Please log in for more thread options Mike wrote:
> Well timing has to be rather critical. its being used in a narrow band
> video sync. so it has to be accurate. > > Well, see i play around with NBTV scanning disk television as a hobby. > I was going to make an NBTV emulator with a 32x48 LED matrix. > > since it is a 32 line resolution, at 12.5 frames per second, you have > a line sync of 400hz. > > the problem is theres 48 vertical resolution pixels per 1 line scan. > so that means i would have to multiply my 400hz pulse by 48 or 19.2khz > to scan the vertical LEDs to keep them in sync. > > Im going to be using an ATmel AVR, so if you know of a way to make a > multiplier out of an AVR CPU. let me know. > > Thanks! Do pretty much what Joerg said. If the AVR has a timer capture function with all the right features, then it can be pretty direct. The narrative below tells how to do it on an 'ideal' system; you'll have to see if your AVR will cope. Set up a timer to run at a nominal 19.2kHz, with the fastest incoming clock that you can get away with. Then set up your 400Hz sync to trigger the timer capture, and interrupt the processor at the same time. Each time the processor gets interrupted, look at the capture register. If it's bigger than 1/2 the timer period subtract the timer period from it, to make it into a signed phase error. Then take that phase error and feed it into a PID filter (most likely you just need a PI filter) that controls the period register value. See http://www.wescottdesign.com/articles/Sampling/pidwophd.html for tips on tuning your PI filter. Fortunately this is a hobby project, so the most important specification you have to meet is "am I having fun yet". It's amazing how much stress you can relieve by temporarily abandoning things like fast lock, absence of overshoot, and noise immunity while you're concentrating on getting a pretty picture. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html | |||||||||||||||||||||||||||||||||||||||||||
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Posted by Joerg on July 4, 2008, 4:14 pm
Please log in for more thread options Tim Wescott wrote:
> Mike wrote:
>> Well timing has to be rather critical. its being used in a narrow band
>> video sync. so it has to be accurate. >> >> Well, see i play around with NBTV scanning disk television as a hobby. >> I was going to make an NBTV emulator with a 32x48 LED matrix. >> >> since it is a 32 line resolution, at 12.5 frames per second, you have >> a line sync of 400hz. >> >> the problem is theres 48 vertical resolution pixels per 1 line scan. >> so that means i would have to multiply my 400hz pulse by 48 or 19.2khz >> to scan the vertical LEDs to keep them in sync. >> >> Im going to be using an ATmel AVR, so if you know of a way to make a >> multiplier out of an AVR CPU. let me know. >> >> Thanks! >
> Do pretty much what Joerg said. > > If the AVR has a timer capture function with all the right features, > then it can be pretty direct. The narrative below tells how to do it on > an 'ideal' system; you'll have to see if your AVR will cope. > > Set up a timer to run at a nominal 19.2kHz, with the fastest incoming > clock that you can get away with. Then set up your 400Hz sync to > trigger the timer capture, and interrupt the processor at the same time. > > Each time the processor gets interrupted, look at the capture register. > If it's bigger than 1/2 the timer period subtract the timer period from > it, to make it into a signed phase error. Then take that phase error > and feed it into a PID filter (most likely you just need a PI filter) > that controls the period register value. See > http://www.wescottdesign.com/articles/Sampling/pidwophd.html for tips on > tuning your PI filter. > > Fortunately this is a hobby project, so the most important specification > you have to meet is "am I having fun yet". It's amazing how much stress > you can relieve by temporarily abandoning things like fast lock, absence > of overshoot, and noise immunity while you're concentrating on getting a > pretty picture. > The best stress relief will be that you don't have to whip it through a standards body review process, EMC certification and all that. Got to do one of those again next week. Oh what fun ... where's that tequila bottle? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. | |||||||||||||||||||||||||||||||||||||||||||
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> video sync. so it has to be accurate.
>
> Well, see i play around with NBTV scanning disk television as a hobby.
> I was going to make an NBTV emulator with a 32x48 LED matrix.
>
> since it is a 32 line resolution, at 12.5 frames per second, you have
> a line sync of 400hz.