NBTV/SSTV-625 Up Converter MkIII

Where it all started as far as most are concerned and saw heavy use from the 60s through to the 80s. Colour and Hi-res modes have unfortunately pushed this system into the backwaters of SSTV. Time to resurrect interest in this simple analogue system.

Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Sat Dec 21, 2019 2:00 pm

Mentioning the software, a large percentage will be a migration from the MkI with changes to serial I/O RAM from parallel, minor tweaks as a result of the different external hardware, and the change in logic supply voltage.

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Dec 23, 2019 1:54 pm

Yesterday I spent a good deal of time considering replacing the Read Processor with a 20-pin device. I have quite a few 18F14K50s in stock but because it has USB I/O it has one output fewer than I need...damn! I'll look into others...

There's an example of "It will change...", hence my suggestion not to start on anything yet...even the power supply, even though it's fairly well defined I have already made more changes that I haven't placed here yet.

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Dec 23, 2019 3:52 pm

Major change #2...

The Read Processor (IC102) is now a 18F14K22 device, a 20-pin DIL chip. This does have enough I/O and all other requirements.

Revised circuit in due course...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Mon Dec 23, 2019 5:09 pm

Revised circuit, however, do not build until I have done the software and made sure the thing works!!

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SSTV-625 MkIII Main 1 v2-Model.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 4:02 pm

Minor changes to the power supply too...but don't order parts or start build yet...

But, no heatsinks required...

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SSTV-625 MkIII psu 1.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 4:16 pm

Here's the interim optional SSTV analogue baseband output... the filter may not be required...we'll see...or it may be simplified...

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SSTV-625 MkIII Baseband 1.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 4:25 pm

RAM and 625 output as things are as of today...

...again do not build as yet...you'll notice my comment in blue r.e. the blanking arrangement, until I'm certain about this, and I repeat (again, yes, I know, boring - "Do not build")...

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SSTV-625 MkIII RAM Output 1.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 4:27 pm

...and that, ladles and germs should be about the extent of this device....there are a few front panel controls to add - simple stuff...

The items in blue are generally notes/reminders to myself...please ignore...however, the red "NOT FOR CONSTRUCTION" notes should be heeded. They will turn green when it gets to the "For Construction" stage.

As I've mentioned elsewhere, I post these interim drawings so that the evolution of the device can be followed...

Until a 'Sticker' appears on any drawing do not order parts or start construction..design is an iterative process..."An iterative process should be convergent, i.e., it should come closer to the desired result as the number of iterations increases."

Watch this space...

Steve A.

When I'm happy with others replicating this I'll post up a pdf file with the final designs, until then, please be patient...however a PCB for this has been raised and may come to fruition...if the PCB could be also used for the NBTV-625 version that makes it doubly worthwhile...trying to do both in one unit may prove tricky, but I'll have a go at it....

Even a kit perhaps?
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 7:34 pm

Now, the coding...there's far more program memory in both PICs than is required. In the MkI the Read Processor used just this amount of code...

Code: Select all
MEMORY USAGE MAP ('X' = Used,  '-' = Unused)

0000 : XX------XX------ XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0080 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
00C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0100 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0140 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0180 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
01C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0200 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0240 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0280 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
02C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0300 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0340 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0380 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
03C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0400 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0440 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0480 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
04C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0500 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0540 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0580 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
05C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0600 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0640 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0680 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
06C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0700 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0740 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0780 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
07C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0800 : XXXXXXXXXXXX---- ---------------- ---------------- ----------------
0000 : -XXX-XX-XXXXXX-- ---------------- ---------------- ----------------

All other memory blocks unused.

Program Memory Bytes Used:  2059
Program Memory Bytes Free: 63477

Errors : 0
Warnings : 0 reported, 0 suppressed
Messages : 0 reported, 0 suppressed



In the Write Processor it was even less...

Code: Select all
MEMORY USAGE MAP ('X' = Used,  '-' = Unused)

0000 : XX------XXXX---- XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0080 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
00C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0100 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0140 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0180 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXX--
7000 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
7040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
7080 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
70C0 : XXXX------------ ---------------- ---------------- ----------------
8000 : XXXXXX---------- ---------------- ---------------- ----------------
0000 : -XXX-XX-XXXXXX-- ---------------- ---------------- ----------------

All other memory blocks unused.

Program Memory Bytes Used:   649
Program Memory Bytes Free: 64887

Errors   :     0
Warnings :     0 reported,     0 suppressed
Messages :     0 reported,     0 suppressed


So there might be a little more with this MkIII version, but not that much...I hope...

In the MkI it was more about the amount of I/O required rather than the code space...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Klaas Robers » Tue Dec 24, 2019 8:59 pm

Steve, I see that you use the output of the DAC-08 as a voltage source. As far as I remember the voltage at the pin that you use as output should be kept at a constant voltage. It is not impossible that the contouring that I observed on your photograph is caused by that configuration.

Any way, if you build it, try to test it with a saw tooth as a digital input signal and check that there are no hick-ups in the output signal. From the past I know how difficult it is to get a smooth ramp, but it is possible.

May be that the first transistor, following the DAC08, should be in grounded base, so an emitter input. Then the input impedance is very low. Good luck.
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Tue Dec 24, 2019 9:22 pm

Klaas Robers wrote:Steve, I see that you use the output of the DAC-08 as a voltage source. As far as I remember the voltage at the pin that you use as output should be kept at a constant voltage. It is not impossible that the contouring that I observed on your photograph is caused by that configuration.

That is a thought, though the datasheet shows it mainly used as a current source into a resistor, but yes. a very valid suggestion. It could also extend the bandwidth...not that we need it here...

Klaas Robers wrote:Any way, if you build it, try to test it with a saw tooth as a digital input signal and check that there are no hick-ups in the output signal. From the past I know how difficult it is to get a smooth ramp, but it is possible.
I'll do that, for sure...just a temporary chunk of code for this purpose...

Klaas Robers wrote:May be that the first transistor, following the DAC08, should be in grounded base, so an emitter input. Then the input impedance is very low. Good luck.

That is an obvious and easy implementation. Good suggestion! It wound (potentially) reduce the following emitter follower's current consumption too by biasing the grounded base stage to a sensible voltage/current.

Thanks Klaas, I'll look into it...another example of it might or will change...

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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Dec 25, 2019 2:11 pm

Here's an initial attempt at a revised output stage as a result of Klaas's suggestions.

Remember, this is interim and untested....I may change a few values here and there, e.g. R205.

Steve A.
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SSTV-625 MkIII D-A 1l.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Dec 25, 2019 4:50 pm

Here's the changes made to the previous posting...

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SSTV-625 MkIII D-A 1l.gif
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Dec 25, 2019 5:08 pm

I've just looked up the DAC (DAC-08, DAC0800) on the Farnell/Element 14 website in the UK, it's no longer stocked by them. There'll probably be other suppliers who have them, it depends where you are. If those considering building this could quickly check their supply situation...

Update...I looked again at the Farnell/Element 14 website, they do have them, and in DIL/DIP - I must have set a filter wrongly...Stock No. 9604448 (166 in stock as of today) and 3118585 (awaiting delivery of 400 early Feb.).

Also, though RS UK have them they're only available in SOIC SMD packages, no DIP/DIL.

If these devices are going obsolete I'll have to re-think this...they have been around for a long long time...

Don't confuse them with the DAC0808, quite a different device...

Steve A,

If this were for a SSTV or NBTV output a R-2R ladder would be OK, but at 625 speeds I doubt it...though it may be possible.

Criclewood Electronics (UK) have the DAC08EN at 5.00+VAT (somewhat expensive), I dare say Alibaba and E-bay too.

If you find an alternate supplier perhaps you could post here with the details/link.

However, if going to the trouble of making a PCB, you really don't want to re-do a PCB a little while later when you have to change the DAC for something else. I really would prefer to find an alternative...a 10 or 12-bit device would be OK, just don't use all the bits, but it needs to be parallel and video speed...not many of those around!

This is similar to the problem of obtaining CA3306's for the 625-NBTV converter of years ago. They are most definitely obsolete now. You DO NOT want to deal with those 'obsolete component' sharks!
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Re: NBTV/SSTV-625 Up Converter MkIII

Postby Steve Anderson » Wed Dec 25, 2019 8:32 pm

Would you believe it? There's a local supplier within a few km of me who has several hundred of these devices at around US$1.70 (DAC0800LCN or DAC-08EP) in DIL/DIP packaging! Right on my doorstep! I don't need them as I already have a few, perhaps add them in with the pre-progammed PICs?

So for the time being I'm going to continue on as things were...though I will keep in mind replacing the DAC0800/DAC08.

Steve A.

....AND 67 of the CA3306 at around US$3.00 each...DIL/DIP packaging...same supplier...though fairly close, they're in an awkward part of Bangkok to get to, cash only, no mail delivery. That's typical here! "Credit Card? What's that?"
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