computer SSTV 1987

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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computer SSTV 1987

Postby Harry Dalek » Thu Sep 06, 2018 10:30 pm

I forgot how cutting edge computers and sstv were in the 80s...well things did improve :wink:
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1987-jan-09.jpg
1987-jan-10.jpg
1987-jan-11.jpg
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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Harry Dalek
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Re: computer SSTV 1987

Postby Steve Anderson » Wed Sep 12, 2018 5:43 pm

Interesting program, but in Basic...no thanks...though DOSBox may well run it if converted to Qbasic.

But how I wish people commented their code, here's a small chunk of mine for the SSTV-625 up-converter...

Anything that starts with a ';' is just text and all after ignored as far as the processor/assembler is concerned. (A REM in BASIC).

;**************** SSTV Main Program *******************

SSTVinit
movlw B'00000001' ; Set up ADC, left justified, no Tacq, A/D clock 1us.
movwf ADCON2 ; ANSELA and TRISA already set up in Init routine.

movlw B'00000001' ; Input AN0 (video input), ADC ON.
movwf ADCON0 ; ADCON1 at reset values.

; movlw 0xF7 ; Calculated values for 4151Hz interrupt (US rate). Temp. (Nom. 0xF784 T0 value).
; movwf SampH
; movlw 0x84
; movwf SampL

movlw 0xF9 ; Calculated values for 4654Hz interrupt (EU rate). Temp. (Nom. 0xF949 T0 value).
movwf SampH
movlw 0x49
movwf SampL

movlw 0x7F ; Initial sync-level value. Sync x4 stage = 1.2V, half = 0.6V, Ref = 5V, at 8-bits, 0.12 = 30.6, say 31.
movwf SyncL ;

movlw B'10001000' ; Set up TMR0, ON, 16-bit mode, internal clock at 8MHz, no pre-scaler.
movwf T0CON

movff SampH,TMR0H ; Load TMR0.
movff SampL,TMR0L ;

movlw B'10100000' ; Enable T0 interrupts, clear any others.
movwf INTCON
SSTVloop
bra SSTVloop ; Endless loop awaiting interrupt from TMR0.

-----------------------------

It simply makes things easier, especially if the author (me) has to return to the code in the future.

The above is just a very small chunk of code used as an example, it's useless as it is.

Steve A.

Note: Code is for PIC18 devices, you won't find some instructions available for PIC12/16 devices, e.g. movff
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Re: computer SSTV 1987

Postby Harry Dalek » Wed Sep 12, 2018 6:23 pm

Steve Anderson wrote:Interesting program, but in Basic...no thanks...though DOSBox may well run it if converted to Qbasic.
It simply makes things easier, especially if the author (me) has to return to the code in the future.The above is just a very small chunk of code used as an example, it's useless as it is.
Steve A.


Having to type it all in and perhaps if it works recording it on audio tape ..i recall this old system why back when your cassette was your storage system ...I didn't take to it as the results for the programs at the time seemed a little poor for the effort .
Sounds like this slow scan program ran on some thing like this Tandy machine ...
Good to see your code Steve is coming together ,results should be impressive next to the slow scan dot matrix printout of this old program ! 8)
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download (13).jpg
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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Harry Dalek
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Re: computer SSTV 1987

Postby Steve Anderson » Thu Sep 13, 2018 5:30 pm

I must admit I've not tried printing any SSTV results I've managed thus far, but I think considering the processes the original photo has to go through it's not so bad a result.

Here is a sample original, cropped to 512x512 pixels and monochrome, and the resultant display via the 'old' version of the SSTV-625 up-converter. The slight aspect ratio distortion is probably down to the 625 TV not being set up quite correctly...in the 'old days' TVs had a height control, usually on the back of the to set the aspect ratio somewhere near correct - I assume these days it's internal.

The process involves the following steps...

1) Crop original JPEG to 512x512 pixels and convert to greyscale (Irfanview).
2) Save as TIFF file (uncompressed).
3) Strip off any header/footer data to leave the raw image information.
4) Send file to TIFF-SSTV converter - a totally separate hardware device to the up-converter. Not published or mentioned before, uses DDS to generate output,
5) Record SSTV audio on laptop/PC and save.

6) Playback SSTV file and view via up-converter. Capture image via camera pointed at screen. Post.

The output is Copthorne McDonald's original standard modified slightly to 128 lines, around eight seconds per frame.

The pub is 'Ye Old Kings Head (YOKH) in Church Street, Epsom, Surrey, UK. Drop in for a swift one if you're in the area...(right opposite St Martin's Church...most UK pubs are somewhere near a church!)

I chose this subject not only 'cos I like imbibing, but it has a lot of detail...honestly!

Steve A.
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YOKH Epsom UK 2.jpg
YOKH Epsom UK 2.jpg (71.41 KiB) Viewed 302 times
YOKH Epsom UK 3.jpg
YOKH Epsom UK 3.jpg (42.08 KiB) Viewed 302 times
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Re: computer SSTV 1987

Postby Harry Dalek » Fri Sep 14, 2018 12:57 pm

Yes Steve there is still a lot of detail that image after all that processing .
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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Harry Dalek
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Joined: Fri Sep 26, 2008 4:58 pm
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