Vintage SSTV transmit converter

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Mar 02, 2024 8:52 pm

Steve Anderson wrote:There are plenty of 8-bit ADCs 'out there' that are fast and accurate enough for what we need here, but invariably they're in non-hobbyist-friendly packaging. I can handle SOIC with a SOIC-to-DIL PCB (an example below), but anything with a less than 1.27mm pin-pitch is a non-starter for me. The DIL package is in its death-throws today, many chips are launched these days with several choices of SMD packaging, but no DIL/DIP option. Progress again.

Steve A.

Note the slightly bent pin (12)...even pin 9 looks a bit suspect...they should have chosen a better example to photograph...even some of the pins look a bit corroded...

SOIC14-to-DIP14.jpg


Its sort of sad as unless there's a market for this stuff it will just get smaller and impossible to solder by hand like your mentioning :(
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Mar 02, 2024 9:19 pm

Steve Anderson wrote:I'm sure I've mentioned this elsewhere fairly recently, 555s can/do introduce quite a severe pulse into the supply at some point in their timing interval, I'm not sure when, but it's there. Thorough bypassing of the supply locally with a 100n disc-ceramic cap and a small (10-47uF) electrolytic should mop that up.

If you Google "555 timer power glitch" or similar you'll end up with many results. A CMOS version might help, but that depends on if it can drive the load.

The ultimate solution is to avoid 555s entirely as I try to.

There are plenty of alternatives in the 74LS/HC/AC etc. series designed to peacefully mix with other logic chips when used as a monostable. For an astable/oscillator likewise.

Other advantages of TTL monos is being able to choose which edge they're triggered on, whether they are re-triggerable or not, and often they'll provide both polarities of output pulse simultaneously. Flexible or what?

Even so, most who design circuits will say, "Try not to use monostables unless you really have to", with an emphasis on 'really have to', including myself.

Steve A.


Yes the 555 is a quick and dirty clock very voltage sensitive to its frequency output but handy when you need one ,i didn't know about introducing quite a severe pulse into the supply i will check i didn't notice this yet but i will look .

I like crystal clocks but is there any thing these days that's a variable clock but does not drift off its set frequency near to what a single frequency crystal clock can do ? if not why not ? I would think it would be complex but must of been done by now its been a long time since the 555 was made must be lots of improved clocks in our era .
The TTL side apart from crystal clocks as the main starting point for them ,i do like TTL mono's yes very useful .
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sun Mar 03, 2024 1:55 pm

The rather rapid and large (100mA or so) current pulse a 555 draws from the power supply is apparently when it switches. Whether at the start or end of the timing interval, or both, I don't know. I would assume both. Ripple or a poorly regulated supply can play havoc with its timing. It can also be mis-triggered by rubbish on the power rail too. And like all monostables subject to the tolerances, temperature coefficients and aging of the external R and C timing components. Some monos have an internal resistor that may form part or all of the resistive timing components. Being Silicon-based its temperature characteristics are 'wild', and the tolerance likewise.

The 555s are/were amazing devices when launched in the 60s and are still made in their millions. A testament to their versatility. However they come with caveats (gotchas). But as mentioned already, avoid monostables generally were you can. A counter fed from a crystal-derived source is far better, but it maybe awkward/impossible/complex/expensive to incorporate.

A worthwhile read on the history of the 555 follows, I got the decade wrong, it's from the early 70s...

https://www.eejournal.com/article/happy ... -timer-ic/

I also like this which I quote from the above, a fact that many forget...

"Hearing is analog. Vision, taste, touch, smell, analog all. So is lifting and walking. Generators, motors, loud-speakers, microphones, solenoids, batteries, antennas, lamps, LEDs, laser diodes, sensors are fundamentally analog components.

“The digital revolution is constructed on top of an analog reality.”


As I'm known to say, "The world we experience is analogue." I'm English, so I choose to spell 'analogue' that way. That is a binary decision!

Steve A.
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Re: Vintage SSTV transmit converter

Postby acl » Mon Mar 04, 2024 9:20 pm

Hi there peeps.
Manged to do a little more this weekend but it will be a long term project. As I continue I will send waveforms that I have on my system. I have initially constructed the converter on a baseboard so I can get access to the components, this is my way of doing things.

IMG_4671.JPG
Boards in position for testing


IMG_4672.JPG
Front panel controls


IMG_4589.JPG
Same treatment on my version of Karen Orton's 30/32 line to 625 converter
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Mon Mar 04, 2024 10:33 pm

acl wrote:Hi there peeps.
Manged to do a little more this weekend but it will be a long term project. As I continue I will send waveforms that I have on my system. I have initially constructed the converter on a baseboard so I can get access to the components, this is my way of doing things.


Again very neat Chris i like seeing how others construct yes understand spare time is a problem on these things,i was going compact to fit in that case i had yours is a nice way to just get it working with space with that lay out i will watch and learn.

Yes look forward to seeing how it gos ,i was looking at the A/D ca3306 scope the other day and i am feeling the result out looks messy i will show signal next time .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Vintage SSTV transmit converter

Postby acl » Sun Mar 10, 2024 2:47 am

First thing I need to test this thing is a reliable 625 line CCIR monochrome signal source so I decided to go down the dedicated ZNA234 chip running a 2.5 meg crystal for 625 line operation

gen.jpg
Circuit
gen.jpg (62.53 KiB) Viewed 402 times


IMG_4675.JPG
On test


IMG_4679.JPG
Don't you just love Veroboard


IMG_4678.JPG
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sun Mar 10, 2024 12:09 pm

acl wrote:First thing I need to test this thing is a reliable 625 line CCIR monochrome signal source so I decided to go down the dedicated ZNA234 chip running a 2.5 meg crystal for 625 line operation


Good idea to go with a monochrome signal not heard of that chip before .

I have put my go aside for now i am thinking its come down to the ram got 2 but i am thinking both are faulty ,i want to see what you get out of the A/c chip compare scope results
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon Mar 11, 2024 1:10 pm

acl wrote:....so I decided to go down the dedicated ZNA234 chip running a 2.5 meg crystal for 625 line operation...
If I remember correct the ZNA234 generates a non-standard/simplified vertical pulse train. For many applications, including here, it probably won't matter. But keep it in the back of your mind...

Also the circuit previously posted and those within the attached datasheet do not provide the standard 75R output impedence. In most applications this again may not matter, but if the item it's feeding has a filter on the input it could well generate overshoot or other artifacts on the waveform.

I have seen a circuit (somewhere) where the output had a filter to bring the rising/falling edges within CCIR specs and provided a 'proper' 75R output, I'll try and find it...however, considering its simplicity as presented it should be a useful item.

Steve A.

ZNA234.pdf
(314.34 KiB) Downloaded 17 times


OK, found it. From the BATC, see page 4...delete IC2 if you don't need those pulses elsewhere...
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Micro-and-Television-Projects.pdf
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon Mar 11, 2024 5:34 pm

I just looked up the cost of the ZNA234 from a well-known UK supplier...GBP 35.00 each! They're having a laugh! I can get them here for 370 Thai Baht inc. local VAT, (7%), the equivalent of GBP 8.15, in DIL/DIP packaging, in one-off quantities. They have over 500 in stock. You might understand now why I don't live in the UK, even though it might be my 'homeland'. But not any more.

Steve A.

P.S. I'm planning to be in the south London/Surrey area from late May until early June this year. Fancy a chat over a few beers somewhere convenient?
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Vintage SSTV transmit converter

Postby acl » Mon Mar 11, 2024 6:25 pm

pattern.jpg


Thanks for info Steve. I think there was a ZNA134 that only produced the synch signals

Managed to get one on eBay. If you look at the acknowledgments in the BATC book you will see that I was involved with producing the some of the prototypes. Let us know more details about your visit to the UK later.

Chris
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Mon Mar 11, 2024 6:58 pm

Well, that's a better price! And in-line with what I can get them for here...though a small micro, a simple resistive D-A, and some code could do far more.

As for my UK visit, the dates aren't set in stone yet, I want to see my mother, sure, but otherwise I want the UK visit to be as short as is reasonable. The UK is simply too expensive to stay longer than really required.

An Aussie friend of mine who also lives here in Bangkok says the same about Australia. He couldn't afford to go back and live there...

Steve A.
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Re: Vintage SSTV transmit converter

Postby Klaas Robers » Mon Mar 11, 2024 10:54 pm

I see in the documentation that this IC gives equalisation impulses and raster seration pulses according to the CCIR standard. And this is needed if the signal gives an interlaced signal. Otherwise the monitor might not give a true interlaced signal.

In the beginning I did se a crystal of 2.520 MHz, but that is only if you want to have an NTSC compatible signal. For PAL (625 lines 25 Hz) it should be 2.500 MHz and that is what Chris did.

Well done.
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Re: Vintage SSTV transmit converter

Postby acl » Mon Mar 11, 2024 11:25 pm

Why thank you kind sir,

The only difference I can see in my original is pin 2 tied to zero instead of plus five Volts and the crystal frequency. Obviously having a known good reliable video signal will allow me to test the converter out.

Regards Chris
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Wed Mar 13, 2024 2:45 pm

Although at the moment the supply situation of the ZNA234 seems reasonable except from those that are dubious and/or from rip-off suppliers. it would be quite an easy exercise to replace it with a pre-programmed micro. This would add the possibilty of more patterns, perhaps more useful ones. Even allowing for selectable 405/525/625. The micro could be in a 14, 18, 20 or 28-pin DIL/DIP package depending on the amount of front-panel controls required.

If controlled via RS232/485/or a USB-UART 'cable' from a PC, maybe no front-panel controls at all.

I think for most here a monochome-only device would suffice. A composite colour device would be far more complex. But a RGB/YUV version is entirely possible. I prefer to avoid composite modes (PAL/NTSC/SECAM) if possible.

There could well be some already implemented, the index/back-issues of CQTV (the BATC) may turn up something useful. Though probably not in recent times, CQTV seems to have gone almost all-digital...which is to expected today.

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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sat Mar 16, 2024 5:05 pm

I'm seriously considering following up on my posting above. The ZNA234 provides a limited selection of patterns, any suggestions as to any additional patterns that would be useful? A full-blown 'Test Card C' (405-lines) or 'Test Card F' (625-lines, but monochrome) is too much for a simple micro and would require some external memory. I'm trying to do a simple replacement for the ZNA234 even though it's still quite available, but with suggested improvements from you guys.

Interesting to note that the datasheet for the ZNA234 mentions a current consumption of 135mA typical at 5V, that's 675mW. It must run quite warm in a 16-pin DIL/DIP package! Maybe an IC socket is not such a good idea? Also with a 2.5MHz crystal the timings could be a little off, but just in-spec. My version probably wouldn't be any different even using a 10MHz crystal. A faster micro could well improve that, but for the uses this might be put to, of no significant consequence.

At first this would be a 625 device only, but there's enough program memory to make it switchable between 405 or 625 if needed. 525 could be added, but I suspect almost zero demand for it. 525 might also require a different crystal, as per the ZNA234 at 2.520MHz or a multiple. Though 6, 12, 18 or 24MHz should be fine.

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