Old-fashioned SSTV?

[GK]

Does anyone still build their own SSTV equipment these days?

I've had an interest in slow scan TV for a while already, although I have next to no interest in playing with SSTV PC/computer programs. I've been searching on and off for a long-persistence P7-type phosphor CRT for a while now to make a traditional analogue monitor for 120/128 line monochrome images, but nothing has turned up yet. I have a heap of short/medium P1 CRTs, so I've decided to knock up a hybrid analogue/digital monitor in the mean time. I've got most of the circuitry figured out on paper for a video digitiser for the image transmitting unit, but that will be a separate standalone system to the receiver/monitor. For now I've just finished drafting the schematic for the latters video display board.

This board contains the video memory and associated circuitry to generate the video display on what will be the units internal CRT or an externally connected CRO. I think it's fairly self-explanatory, but the frame rate is 61Hz, 128 horizontal lines with 256 pixels per line. 8-bit digitization is used for the video luminescence. All signals are derived from the free-running 15-bit synchronous counter to the left. U10+U11 produce the horizontal deflection sweep signal while U12+U13 handle the vertical. The 15-bit counter is positive edge-triggered. On the negative edge of the counters master clock the data output of the video memory SRAM is synchronously shifted to the parallel video DAC via octal DFF U19. During the hoz. and vert. retrace intervals the video DAC is blanked by asserting U19s asynchronous reset input and forcing the analogue video output to a negative level blacker than black.

A uC-based demodulator/receiver and digitiser will be accommodated on a separate PCB. The uC on this board will assert access to the video memory for writing via the 74HC573 tri-state buffers wired as parallel data bus multiplexors/selectors.

The SRAM is large enough to hold four individual received images. To this end the two MSBs of the SRAM are binary-decoded by a small diode matrix for a 4-position rotary switch which will be used for selecting the image/page to be displayed.

Should get around to starting the board layout tomorrow evening, though I'm going to have to start hunting for some recordings of 7/8 second SSTV images so I have something to decode when the monitor is complete.

[German_EE]

Ah! Happy memories!

I did it the old fashioned way in the late 1970's just after I got my Class B Licence, an old 7-second phosphor tube (any color you like so long as it's yellow) and a load of electronics on Veroboard. I transmitted a few SSTV images just to prove that it worked but most of the activity was receiving on 20m. Monitoring a typical QSO with an Italian station went something like this.................

Here is a picture of my house

Here is a picture of my shack

Here is a picture of my wife

Here is a picture of my girlfriend 

All of this of course at seven seconds an image in bright yellow whilst sat in a darkened room. Digital makes things too easy.

Good luck with your project.

[KJDS]

I've not seen SSTV in 32 years. I'd almost forgotten it's existence.

[jopie]

Nowadays you would be using a sound card together with some software to display SSTV images. No need for complicated hardware...

[wkb]

I've not seen SSTV in 32 years. I'd almost forgotten it's existence.

There are regular SSTV transmissions from the ISS:

http://ariss-sstv.blogspot.nl

So it is by no means dead.

Wilko

[vk3yedotcom]

You can get SSTV apps for your mobile phone.  Holding the phone up to a transceiver speaker and microphone allows receive and transmit.

There are also online SSTV receivers.  These ones are in Australia but there's a link to those elsewhere also http://users.tpg.com.au/adslsymb/VK6AAL/Live_Cams/AusCams.htm

[bench_knob]

Hi there,

I too always had a fascination for SStv. Never got around to doing anything.

Your project seems it could be a fun project. You gonna do it all old-skool? Wire-wrap or PCB?  I still have quite a bit of ww materials laying around for projects. Sometimes I make a PCB using toner-xfer ( http://www.pulsarprofx.com/ .. reliable and works good), but I still like wire-wrapping digital circuits. Parts are abundant and cheap too. Of course you could do it with an FPGA, but what's the fun in that? And you sound as though you wanna do old-skool!

I took a quick peak at your sch, it seems it'll likely work. May have to fiddle a bit re; load timing, but it looks like you got a good handle on things.   

Some toobs...

eBay: If you can deal with a small square screen, there's an Dumont 4FP7, electrostatic defl CRT for $40 USD, Itm:252323497372

Or via eBay again:

round 7" Dumont KC2495-P7 electromagnetic deflection CRT, $28 USD: 131863119442

Good luck, and have fun..let us know how things work out.

bench_knob

==========




Quote from: GK on July 26, 2016, 11:37:12 PM

Does anyone still build their own SSTV equipment these days?

I've had an interest in slow scan TV for a while already, although I have next to no interest in playing with SSTV PC/computer programs. I've been searching on and off for a long-persistence P7-type phosphor CRT for a while now to make a traditional analogue monitor for 120/128 line monochrome images, but nothing has turned up yet. I have a heap of short/medium P1 CRTs, so I've decided to knock up a hybrid analogue/digital monitor in the mean time. I've got most of the circuitry figured out on paper for a video digitiser for the image transmitting unit, but that will be a separate standalone system to the receiver/monitor. For now I've just finished drafting the schematic for the latters video display board.

This board contains the video memory and associated circuitry to generate the video display on what will be the units internal CRT or an externally connected CRO. I think it's fairly self-explanatory, but the frame rate is 61Hz, 128 horizontal lines with 256 pixels per line. 8-bit digitization is used for the video luminescence. All signals are derived from the free-running 15-bit synchronous counter to the left. U10+U11 produce the horizontal deflection sweep signal while U12+U13 handle the vertical. The 15-bit counter is positive edge-triggered. On the negative edge of the counters master clock the data output of the video memory SRAM is synchronously shifted to the parallel video DAC via octal DFF U19. During the hoz. and vert. retrace intervals the video DAC is blanked by asserting U19s asynchronous reset input and forcing the analogue video output to a negative level blacker than black.

A uC-based demodulator/receiver and digitiser will be accommodated on a separate PCB. The uC on this board will assert access to the video memory for writing via the 74HC573 tri-state buffers wired as parallel data bus multiplexors/selectors.

The SRAM is large enough to hold four individual received images. To this end the two MSBs of the SRAM are binary-decoded by a small diode matrix for a 4-position rotary switch which will be used for selecting the image/page to be displayed.

Should get around to starting the board layout tomorrow evening, though I'm going to have to start hunting for some recordings of 7/8 second SSTV images so I have something to decode when the monitor is complete.

>

[toolmansteve]

My mate who lives in Clacton U.K. has a really good SSTV Website, with all the software you need downloadable.
Try here   www.g0hwc.com  you might find like minded constructors from that site.

Steve MM0ARZ

[LaserSteve]

I have one or two of the crts.

Steve

[SDA]

Hi All,

Whilst doing a Google on the term 'Hardware SSTV Demodulator' up popped this thread. I too have been interested in SSTV since I was 17 or so, and that was a long time ago!

In the light of this I have joined the EEVblog, username SDA.

I also have little/no interest in PC-based SSTV programs, nor any of the modern hi-res and colour modes. i.e. if it's not Cop McDonald's FM monochrome 120/128 line system I'm really not interested. I might read about the newer developments, but don't expect any action at this end!

In recent times I've had the time (at last) to pull together a SSTV-to-625 up-converter, in the attached photos is a photo of the MkI hardware and some of the screen-shots as displayed on a 19" CRT TV.

I'm in the process of building the MkIII version, the MkII was just a paperwork exercise. The MkIII uses less chips and board space.

I was impressed by the circuits posted here and as another blogger said, "It should work". I wonder what progress has been made on this over the past while?

SDA.

...having a few problems with the photos, the help screen isn't that helpful - this blog software is different to the one I'm used to...I'll keep plugging away...

[Yansi]

Hams around here still use SSTV, but just for fun.  Occasionally, I hear SSTV (or, even more often HF-FAX) transmissions on the low HF bands (80, 40, 20 meter).

I undestand your hate for PC-everything. So why not just to build an SSTV receiver using some modern MCU and a small TFT display? Would be a very nice exercise for some basic DSP algorithms...

[SDA]

Well, it's not quite a case of 'hate PC-everything', more I prefer to have a stand-alone system that doesn't rely on a PC. The PC is an incredibly useful tool, where would we be today without them?

In this case the system uses two PIC microcontrollers and puts to use an otherwise unused and forgotten old TV. At every stage the PC has had some input, drawing the schematics, writing the microcontroller software and producing the screen-shots and photos.

As the original poster said, "Does anyone still build their own SSTV equipment these days?" There's a sense of satisfaction of creating something yourself that cannot be matched by loading someone else's software and knocking up a few interface cables and saying it's a 'done deal'. Quick, simple? - yes - but not satisfying - at least to me, but then again I'm old-school I guess.

The PC route is a perfectly valid way of doing things, please don't get me wrong, it's just not the way I choose to do it.

SDA.