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 Feb 24, 2024 3:48 pm

Steve Anderson wrote:Ah yes! The old "Underestimating The PSU" trap, many fall into it, including myself. A cursory glance at the circuit I would guess something like 300 to 500mA at 5V would be about right, plus 100mA on the +/-12V rails. A very very rough guess, it might be considerably less though. If it were changed to using HC devices, maybe 50mA for the 5V. But I don't suggest that at this stage. An indication of this is the size of the supply used in the EA article.

...and that's just the average current. Even an innocent-looking 555 can draw over 100mA for a short period as it switches. This can pull down the +5V rail to below the +4.75V limit for LS devices causing them to misbehave before the regulator has a chance to respond. My usual rant r.e. supply bypassing and heavy-duty earth/grounds shouldn't need repeating. The answer, put a large (100uF+) cap on the output of the regulator in addition to all the 10n/100nF bypass/decoupling caps.

In many articles published problems DIY builders have eventually get traced back to the supply arrangements. The consensus generally of misbehaving DIY projects is power supply problems are 90% of them.

If the regulator(s) is/are not on the board (e.g. bolted to a metal chassis), place those large-ish caps on the board. The regulators don't need them, the circuit does. But I still place 100nF disc-ceramic caps on both the input and output of 78xx/79xx regulators within 1cm of them wherever they may be, these are for stability such that they don't oscillate. Consider them essential. They cost peanuts, especially if you buy 100 or more at a time. You will (or should) use them up.

The same applies generally to variable regulators (e.g. the LM317/LM337 varieties), but follow the datasheets if in doubt.

Steve A.

A link that outlines the reasons and techniques often used...

https://en.wikipedia.org/wiki/Decoupling_capacitor


Hi Steve
I tended to over the years stay away from a lot of TTL circuits like this one as i have never had much luck with them ever since trying a A&A engineering kit which i failed miserably at ,i came across the old documents the other day i will have to scan them and post it up ,got to be 30 or so years old .
Might find the circuit interesting but at the time i found it very hard to fault find it being new to it all .
Quick preview of what it looked like below before i scan them

WIN_20240224_15_01_13_Pro.jpg


Where i am at here i tried the 82 ohm resistor on the front contrast pot and that worked as you told me the signal better looking at the A/D converter input .
So i will add that .
I am pretty happy with the first part of the circuit .
But when it comes to the TTL part i was never expecting different output results from the LS ic's of different makes ages its pretty much confusing very much so when i am using a new ic ..thats where i am thinking where you mentioned earlier in the project and above it could be a power supply problem ...
i have not looked them up yet data wise but to me it sounds like they all have different minimum to work current needs .
Well i will find out soon as thats my next step i am nearly all out of ideas if its not the power supply .
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 » Sat Feb 24, 2024 5:37 pm

That could well be an interesting read, depending on what VGA standard they used to convert from. I'm not so interested in the colour aspect though.

As for your project currently underway, it has prompted me to make a start on the idea I mentioned a few days back, a TIFF image file to WAV SSTV audio file converter, live output which can be recorded/saved in something like Audacity. Any common image file (GIF, JPG, etc.), can be easily converted/cropped/made monochrome/and re-sized using something like Irfanview. Both programs are current for PCs (Windoze) and free, and useful in their own right.

I did build something similar a few years back which performed the same function. But it did use a large 40-pin chip plus others, this version will be 28-pin, probably 20-pin maximum, and maybe 8 chips total, not including power supply. The first version was the device I used to generate all the SSTV files I uploaded (somewhere) on this forum. I say "somewhere" as I can't find them! Maybe they've been deleted?

Steve A.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Feb 24, 2024 6:28 pm

Steve Anderson wrote:That could well be an interesting read, depending on what VGA standard they used to convert from. I'm not so interested in the colour aspect though.

As for your project currently underway, it has prompted me to make a start on the idea I mentioned a few days back, a TIFF image file to WAV SSTV audio file converter, live output which can be recorded/saved in something like Audacity. Any common image file (GIF, JPG, etc.), can be easily converted/cropped/made monochrome/and re-sized using something like Irfanview. Both programs are current for PCs (Windoze) and free, and useful in their own right.

I did build something similar a few years back which performed the same function. But it did use a large 40-pin chip plus others, this version will be 28-pin, probably 20-pin maximum, and maybe 8 chips total, not including power supply. The first version was the device I used to generate all the SSTV files I uploaded (somewhere) on this forum. I say "somewhere" as I can't find them! Maybe they've been deleted?

Steve A.


I just up loaded it i think that's every thing i had on it ,they were pushing the colour side of it ,i do recall now that did work ! i used it on some naughty CB slow scan transmitting experiments which just jogged my memory ~ ! i was thinking of something thing i built around the time that was built on PCB .
I think i left it behind when i moved to Melbourne what i don't remember was the software and pc hook up side .
Get to read about the FAX add on now
Yes i know of those programs don't worry to much about the PC doing most things these days every one here is interested in building
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 » Sun Feb 25, 2024 9:53 pm

Well i swapped power supplies today which uses a 5 amp transformer and results were pretty much similar ,i am going to have to see how Chris your version gos .
I will try and see if i can at least get it back to where it was starting to work ,i have never had a project where the same parts give different results sort of annoying and intriguing at the same time !
One good thing i have the scope shots of what i should expect .
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 » Mon Feb 26, 2024 9:04 pm

Hi Harry,

Progress a little slow this end as it will take me some time to complete as I have other things to attend to . Anyway here are some pictures of my progress. Main problem is having to order specialised devices singly on eBay and trying to use 'decaffeinated' solder. I have ordered some good old lead solder as the new 'woke ' stuff melts at a higher temp and reacts with the tinning on the resistor legs.

IMG_4668.JPG
Power supply module


IMG_4667.JPG
Synch and ADC conditioning board


IMG_4665.JPG
Digital section Power supplies wired but still wrapping wire to be used underneath board


IMG_4664.JPG
Nearly complete output section
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Tue Feb 27, 2024 7:51 pm

acl wrote:Hi Harry,

Progress a little slow this end as it will take me some time to complete as I have other things to attend to . Anyway here are some pictures of my progress. Main problem is having to order specialised devices singly on eBay and trying to use 'decaffeinated' solder. I have ordered some good old lead solder as the new 'woke ' stuff melts at a higher temp and reacts with the tinning on the resistor legs.


Looks very neat Chris and very well constructed .

I only use lead solder i tried the other greenie type and didn't like it ,Solder very costly these days my last roll was 60 bucks hate to think what is now .

Be interesting to see what your results you get i get very different results on what TTL's i use ,i should of marked the ones that made it work but looks like i will have to check every thing again ,
i will keep an eye on how yours go's .
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 » Tue Feb 27, 2024 9:29 pm

I was confused at first, "Why Chris have you put the components on the copper/solder side of the board?" Some time later I realised that it's a print of the actual copper tracks on the other side. I've not seen that variety before!

I'm not sure what 'colour' of solder I get here, green or otherwise, but it seems to work OK for me. Ah! Just checked, it's good old 60/40. The next time I need to get some I must remember to check. It probably couldn't be sold in the UK so dumped in Thailand. You can also buy 100 Octane leaded petrol here, not at every petrol station though, there's not much demand for it I guess these days.

In the UK you can still get 130 Octane aviation fuel for warbirds. Very limited, hideously expensive and you need a permit/license to purchase it. My 'home airfield', Blackbushe, used to have it up until the 80s, but not now. You're lucky if you can find 100LL (Low Lead), most aircraft have been (expensively) adapted to use 80/87LL. Some can even use Mogas, Motor Gas (Petrol), a US term also used in the UK aviation field, mostly microlights or aircraft that use Rotax engines.

Getting away from solder...and SSTV...

Steve A.
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Vintage SSTV transmit converter

Postby acl » Wed Feb 28, 2024 9:07 pm

7.jpg
Holden Austin 7 Australian


You think you have problems. The one on the right is mine and runs on unleaded premium as the green additives rot rubber, soft solder and turn to water after time so much for progress.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Thu Feb 29, 2024 8:18 pm

acl wrote:
7.jpg


You think you have problems. The one on the right is mine and runs on unleaded premium as the green additives rot rubber, soft solder and turn to water after time so much for progress.


Holden Austin 7 Australian ! never heard of it till now DX information :lol: UK is going Electric is still a while away 2050
I think that stuff is cheaper than lead solder which is starting to cost the price of gold i collect it for the future hoarder i am ,just need to get some flux to reuse it /
I am very interested in how your build go's so get that lead solder !
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 acl » Fri Mar 01, 2024 7:56 am

Harry,

I have some tasks I have to do before continuing but I will persevere with it in time
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Fri Mar 01, 2024 9:13 am

acl wrote:Harry,

I have some tasks I have to do before continuing but I will persevere with it in time


No worries Chris i am at the moment working on mine right now fault finding .....so far i have found the 7474 not outputting any thing so i will replace that ,i was swapping ic's left right and centre a while back so i could of and looks like plugging in a faulty one .
I should be able to get it to operate as before ,
One thing that crossed my mind is the 555 if he used a LM or NE version does not say as i found a while back not all 555's operate the same and its pretty much apart from the crystal clock very critical to this all ..i will see if i have any thing else laying around to test against .
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 acl » Sat Mar 02, 2024 3:44 am

Here you go Harry,

When you get it back to where we left off we will try and get yours working.

555.jpg
Differences
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sat Mar 02, 2024 2:01 pm

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
SOIC14-to-DIP14.jpg (157.86 KiB) Viewed 278 times
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Re: Vintage SSTV transmit converter

Postby Steve Anderson » Sat Mar 02, 2024 2:51 pm

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.
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Re: Vintage SSTV transmit converter

Postby Harry Dalek » Sat Mar 02, 2024 8:50 pm

acl wrote:Here you go Harry,

When you get it back to where we left off we will try and get yours working.

555.jpg


Thanks Chris i just want to see it working mine or yours ,i got it partly going for a bit .
I tried the LM version and i could notice any difference in the operation .
I had a good look at every thing today and i think i might be in trouble the i checked the 74ls161's they are now all working correctly clean pulses with the doubling of timing down the ic chain . so the switching all looks good .........................BUT the output of the ADC is messy i can tell as if i remove the video its still there random pulses and there's a difference if i plug in the spare ram .....What i don't have spare IC to change is the 158 the ram and the ADC to check so i am thinking the faults now are around this area ...the timing controlled from the sync and the clock and the 555 seem ok ...i have to test the ADC on its own again via the 3MHZ clock and i think its just grounding pin6 A/D EN...i need to see this one working that the video is controlling it at the moment i don't think so !
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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