Help with Robot 70A

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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Help with Robot 70A

Postby RetroGameCouch » Sun Aug 21, 2022 7:22 pm

I bought a Robot 70A in a thrift shop the other day for 2.5 euros. Surprisingly (or not) it still works.

I am new to the world of SSTV, but after a night of fiddling and reading I got this result:
https://youtu.be/Y0ezz8zcOa8

On this forum I was able to find the manual, which confirms what I had already gathered:
  • 8s (8 seconds, althought it might also be 7 seconds as that is pal 50hz)
  • 120×120 pixels (I have seen mentions of 128x128 as well)
  • 15 lines per second, to make 120 lines in 8 seconds
  • The vertical sync pulse has a duration of 30ms, and the horizontal sync pulse duration is just 5ms
  • The sync frequency is 1200Hz, and black and white interpolate between 1500Hz and 2300Hz
  • The aspect ratio is 1:1 (to match the usual oscilloscope tubes of the day)

I really want to show off the Robot 70A in a video I am doing about BASICODE (I saw the inventor of BASICODE is active here as well!). Does anyone know how to convert an image to a WAV file that the Robot 70A can decode?
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Re: Help with Robot 70A

Postby Steve Anderson » Mon Aug 22, 2022 11:58 am

A quick-and-dirty way is here:-

https://www.vr2woa.com/sstv/

It isn't exactly in the format you require but should get you started. (The second-to-last option)....

Steve A.

I did upload some files here in the format you need here - somewhere - let me see if I can find them...nope, can't find them here or on my PC...

Here's one to get you started....it's in 128x128 format at EU SSTV rates (16.7Hz line-rate), but it should/might work on the Robot 70...it's sampled at 8kHz, not sure if all wav players will handle it...also off-screen shot of the image...ignore the greyscale ramp at the bottom of the screen-shot, that's not part of the WAV file.


SA0140808.jpg
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SA0140808.WAV
(4.58 MiB) Downloaded 146 times
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Re: Help with Robot 70A

Postby Steve Anderson » Mon Aug 22, 2022 12:41 pm

I did build a TIFF-to-WAV convertor years ago in 2015, (used in generating picture above) but it's more of a hardware solution rather than software/PC based idea. I haven't posted it anywhere. It probably could do with an update before I do anyway.....Later - Yep, it could sure use an update!...or at least a rationalisation...

Steve A.

P.S. I've found the files I was looking for, I can re-upload them if needed...but if I understand correct, you wish to generate your own....

I used 128x128 as it's binary-friendly, and most gear, new or old, should cope with it.
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Re: Help with Robot 70A

Postby Dave Moll » Mon Aug 22, 2022 6:34 pm

Moderator note:

To save confusion, I have deleted the duplicate of the thread-starting post. I have also worked out why the list function wasn't working correctly.
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Re: Help with Robot 70A

Postby Steve Anderson » Tue Aug 23, 2022 6:11 pm

I used the demodulator from the Robot 70(A) for my SSTV decoding for quite some time. Though I like to think I improved it somewhat. I replaced the op-amps with more modern versions, improved the full-wave rectifiers and revised the output filter. The version of the manual (earlier version) I have used 709 op-amps plus those all those pesky compensation components required. The manual posted here uses 741s rather than 709s - that saved a few pennies by eliminating those.

Even so, you'll see that the 741s are in a large transistor-style hermetic packages, not DIL as most know. This made them expensive, hence why the DIL package came along.

A T099 741 would look like below...I have a few LM357 op-amps and others in the same package...will I ever use them? Perhaps I should make an effort to give them a home somewhere...

Steve A.

T099.gif
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Re: Help with Robot 70A

Postby Harry Dalek » Wed Aug 24, 2022 3:55 pm

I never liked that ic design as far as the pins hard to mount ! who ever came up with that idea needs a talking to !
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Re: Help with Robot 70A

Postby Steve Anderson » Wed Aug 24, 2022 4:04 pm

Hmm, I have no problem with it. It's the same as the old-fashioned 3-pin BC107 series, just with five more 'legs'. Fiddly, maybe, but not impossible. Put it this way...which would you prefer? T099 or SMD? I know which I would choose...

The most 'legs' I have seen in a 'transistor-style' package is a T0100 package with 10 of them as well as a 6-pin version (also called T099) for dual transistors or FETs...e.g. LM394 Dual Supermatch Pair (2xNPN)....which I also have a quantity of...also the SSM2210/2212 (NPN) and SSM2220 (PNP) audio series from Analog Devices...coming from AD, they're expensive!...that's why I don't have any of those...though now obsolete (i.e. made of Unobtainium)....

Steve A.

Anyway, getting off-topic (again)!...
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Help with Robot 70A

Postby acl » Wed Aug 24, 2022 6:00 pm

We used to use these 'spreaders' to space leads to form DIL spacing. I assume they used cans for higher spec devices with regards temp drift .

Regards Chris Lewis

spacer8pin.jpg
spreader
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Re: Help with Robot 70A

Postby Steve Anderson » Thu Aug 25, 2022 5:11 pm

We used something similar at Decca Radar in the 70s though the pattern was still circular, it eased insertion into the PCB during assembly.

The metal can variety are often (though not always) still used for aerospace and military spec. chips where the stress of temperature cycling between -40 and +125 Celcius is too much for the plastic DIL packages. Also some larger chips (more then 20 pins) are also made in ceramic packaging for the same reason. It also makes them hellishly expensive.

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