Negating LF problems of NBTV.

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

Re: Negating LF problems of NBTV.

Postby smeezekitty » Fri Aug 07, 2020 7:54 pm

Steve Anderson wrote:P.S. If anyone wants to suggest a future project that I may be able to put together, ideas welcome...e.g. 'B' above, remove the requirement of the PC, record/playback on a SD card as part of the unit. If you've got some older SD cards of 2GB or less hold on to them for this, I really don't want to mess with the e-FAT format, FAT16/FAT32 is OK, though the cards will not use any of the conventional formats...they'll be used simply as a glorified EEPROM - which is really all they are.

Using the same format as the PC-based version of 'B' above, a 1GB SD card will record over three hours of NBTV audio and video.

...however there is a caveat to this... using the proprietary SD card interface requires an expensive (for us lot) licence, the SPI interface is licence-free but of course slower.

FAT32 doesn't limit you to 2GB. It actually supports up to 2TB. Also, the SPI interface on an SD card is plenty fast enough for NBTV
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Re: Negating LF problems of NBTV.

Postby Steve Anderson » Sat Aug 08, 2020 1:35 pm

smeezekitty wrote:FAT32 doesn't limit you to 2GB. It actually supports up to 2TB. Also, the SPI interface on an SD card is plenty fast enough for NBTV

Yes, correct, but there is a reason for mentioning it - just wish I could remember what it was...it's been a while since I dabbled around with SD cards/discs/etc..

It'll come back to me at some point.

Steve A.

Ah! It's something to do with the SD card initialization as I recall, I'll look through my notes from a few years back...something to do with the difference between standard capacity cards and high capacity cards. That breakpoint is either 2 or 4GB...again from memory...

The read/write speed needs to be more than 100kB/s via the SPI interface...I would think that all should be able to meet that.
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Re: Negating LF problems of NBTV.

Postby Andrew Davie » Sat Aug 08, 2020 1:37 pm

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Re: Negating LF problems of NBTV.

Postby smeezekitty » Sun Aug 09, 2020 3:26 am

Steve Anderson wrote:Ah! It's something to do with the SD card initialization as I recall, I'll look through my notes from a few years back...something to do with the difference between standard capacity cards and high capacity cards. That breakpoint is either 2 or 4GB...again from memory...

That's true. And the addressing mode is also different. But the differences are not a big deal and easy to handle
The read/write speed needs to be more than 100kB/s via the SPI interface...I would think that all should be able to meet that.

I believe that the SD cards support SPI clocks of at least 8MHz which would give you about 1MB/s

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ok fixed
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Re: Negating LF problems of NBTV.

Postby Steve Anderson » Sun Aug 09, 2020 1:18 pm

Most of the information r.e. SD & MMC cards I got from this site - it's a bit vague in places but it's a start:-

http://elm-chan.org/docs/mmc/mmc_e.html

The 'proper' reference is from the SD Card Association, but if printed it would make an ideal door-stop - good for bed-time reading too.

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Re: Negating LF problems of NBTV.

Postby acl » Mon Aug 10, 2020 10:57 pm

Hi Steve,

Glad you see you back home at long last. I think that signal generator was used on the SSTV camera we discussed some time ago.

https://www.youtube.com/watch?v=mdEdHKR6lCA

I am still interested in the SSTV convertor and am willining to help out with the prototype if you need help.

Regards Chris Lewis
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Re: Negating LF problems of NBTV.

Postby Steve Anderson » Tue Aug 11, 2020 1:31 pm

acl wrote:Hi Steve, I think that signal generator was used on the SSTV camera we discussed some time ago.


Yes, I saw it in among the gubbings and thought, "What's that?" Found it on the 'net and ordered four more - very useful little device.

acl wrote:"I am still interested in the SSTV convertor and am willining to help out with the prototype if you need help.


I assume you mean the SSTV-625 up-converter? It's work-in-progress but currently stalled due to a whole pile of other things pending, and not just NBTV/SSTV stuff. It would sure help if you (or others) want to be beta-testers/builders of the SSTV-625 up-converter. There's also a 625-SSTV down-converter on the horizon with the intention of also making it 625-NBTV. Same concept as Peter Smith's version of 2000 (CQTV189). PM me if you'd like a copy, or you can download issues of CQTV over one year old from the BATC website:-

https://batc.org.uk/

The biggest problem with the 625-NBTV/SSTV down-converter is finding a suitable A-D device that is fast enough, at least six bits, with hobbyist-friendly packaging (DIP) and at a sane price. Peter used the 6-bit CA3306, now made of Unobtainium. The latest datasheet I have for it is dated Dec 1993.

Two CA3306 chips can be cascaded to form a 7-bit A-D if desired.

Steve A.

Unobtainium (Uo) - a highly desirable material that is hypothetical, scientifically impossible, extremely rare, costly, or fictional, or has some of these properties in combination.

A local supplier has a stock of around 70 of the CA3306 chips at about GBP 2.50 ea. I doubt any more after they've all gone.
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