Moderators: Dave Moll, Andrew Davie, Steve Anderson
AncientBrit wrote:There's always this device that interfaces between USB and TTL RS232
Also ftdi do USB interfacing to memory cards.
Not had time to research further.
(Hope this embedded link works)
http://www.ftdichip.com/Products/EvaluationKits/UM232R.htm
Graham
Klaas Robers wrote:It looks as if the subject faded away from sync to computers.....
The sync is / was needed if you record NBTV video onto compact cassettes or even reel to reel recorders. You never know which speed they run. So a CCIR-like sync was not at all a bad idea in the time that the word computer was very uncommon and digital sound was impossible to think about.
With a running video and a synchronised Nipkow disc you need no frame sync, after you synchronised the frame by hand. The Baird type 30 line monitors still work that way. Even cathode ray tube monitors don't need it, as the frame was alligned at just above 30 lines and synced by the 30th line pulse.
Then we wanted to have an indication of the beginning of a new frame, or the end of a past frame, which is indeed the same. The aim was not to spoil any video information, so a longer sync pulse, like CCIR does, was not an option. Then the missing sync pulse was suggested and accepted, although the knowlegde that it was missing is coming afterwards, somewhere during line 1. But this is not a problem as you are running on some sort of flywheel.
My monitor syncs in this way:
- The disc gives a frame pulse too, which should coïncide with line 1.
- When the two frame pulses are not almost coïnciding the disc is running without sync.
- When the video frame pulse leads, the disc is speeded up slightly
- When the video frame pulse lags, the disc is slowed down slightly
- When both coïncide almost the disc speed is "nominal" and line sync is applied.
To be clear: the disc has a nominal speed, set by hand, in which the frame is almost stable. At this speed the sync circuit can be connected. The other two speeds are slightly higher and slightly lower. Graham would program a pic for it, I did it in discrete logic.
Klaas Robers wrote:It looks as if the subject faded away from sync to computers.....
AncientBrit wrote:There's always this device that interfaces between USB and TTL RS232. Graham
Steve Anderson wrote:AncientBrit wrote:There's always this device that interfaces between USB and TTL RS232. Graham
I had considered that as well as USB to parallel 'cables'. These are obviously more than just a cable. But I wonder just how well they emulate a real LPT1/2/3 port.
If you write to the address for LPT1 data register &H378, does it really work? Similarly reading the status register and writing to the control register.
Anyone have experience with these?
Maplin in the UK have an example, stock code A94BF.
Steve A.
gary wrote:This leads me to feel that whilst they may work for most printers that they do not necessarily provide the full parallel port functionality.
Steve Anderson wrote:The Futurelec product looks ideal, and they have a branch in Bangkok. And for once, a decent datasheet!
Steve Anderson wrote:When you analyse the requirements all we want is a storage device, a PC and all this external paraphernalia is like using a sledgehammer to crack a nut.
Steve Anderson wrote:A simple stand-alone device that read/writes to a CF card would be fine. So I downloaded the Compact Flash specification. Guess what? I gave up yet again.
Steve Anderson wrote:I've got several spare operational hard disc drives kicking around....I wonder?
Steve Anderson wrote:I might start a new thread on this subject, I don't want to clog up this thread which started on the subject of sync pulses.
Steve Anderson wrote:You know, for years I've wracked my brains (what's left of them) over this whole subject of frame sync for NBTV, you have to admit that with the current arrangement only its mother could love it.
There has to be a better way without losing a whole line, or even part of one, to it. I'm not keen on a 'Super White' pulse or a 'Super black-more-than-normal Sync' pulse. Here I'm only concerned with an analogue signal, for a digital one it's real easy.
Come on guys, it can be done. But it has to be compatable with the missing sync system too. Time to get creative. Just because it's been done a certain way for quite a while doesn't mean we need to stick rigidly to it.
Automatic and reliable frame sync has been a pain for such a long time. It's time to put it to bed.
Steve A.
Andrew Davie wrote:My gut feeling, though, is that a variable motor speed, rather than a pulsed system, would be a much easier system to stabilise.
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