Slow Scan Television Experiments

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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Slow Scan Television Experiments

Postby Harry Dalek » Sun Oct 05, 2014 8:57 pm

Slow scan television the original System is always enjoyable to try out with a mechanical twist .

I am trying a camera idea out using mirrors or mirror ,i know an easier way would be a rotating drum on a long screw with a photo wrapped around the drum in the way old fax imaging systems used but with a laser .

But due to the problems i had on the NBTV mirror camera version i am going to try some thing similar here to see and work out problems i had hopefully ,it should be a little more adaptable to different experiments .

For a start i could just not use the frame mirror and mechanically move the sensor and just have the line mirror ,could do a flying spot SSTV camera but my heart is set on a direct light version but any case succeed or fail just show here what i have been up to of late.

My original idea on the mechanical side of things was use some dc motors and pulleys but due to the slow speeds i found it a little sloppy so redesigned it with bipolar steppers see both versions in photos posted here .

The electronic side I have a crystal clock feeding a 4040 which gives me the 15 hz line pulse and some 7490s for the frame pulse , i have put in a opto switch at the mirror corners as the mirrors are where the line control sync should be coming from in a mechanical system .
So i have used a similar system to the last project opto switch to LM311 to a 555 bistable switch so the line mirror is in sync with my clock and the opto switch and LM311 part are used for the line pulse .

SSTV cameras need a Voltage controlled oscillator so my head amp needs vary the frequency of the VCO from 1500 to 2300 from black to white .

Just going to use one of the Free SSTV programs when i get to the point of testing view on PC
Attachments
IMG_8963.JPG
The original idea with dc motors pulleys
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IMG_8972.JPG
The mechanical idea i am trying now with stepper motors
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IMG_8971.JPG
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Last edited by Harry Dalek on Thu Feb 23, 2017 5:14 pm, edited 1 time in total.
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: Slow Scan Television Experiment

Postby Harry Dalek » Thu Oct 09, 2014 1:21 pm

I have been testing the scanning with a laser to see how accurate the mirrors are .

I am not overly happy with the long double sided mirror for the frame scan ,i didn't think the delay between mirror sides would bother me but it does :x

Theres also a slight line wobble between 4 sided line mirror ,i should of used the other plastic mirrors with self adhesive ,does not take much glue to through a mirror off , would not be a problem if i swapped it for the frame mirror since its only using a mirror side perscan.

Having done what i have now i can see i could of done up to this stage a little easier for start i don't think i really need the electronics for the frame pulse i could of got that just via pulse from an opto switch on the frame mirror...so think really just needed the cyrstal clock and 4040 this is gives both the 15 hz and a higher frequency for driving the bipolar stepper ,testing the stepper speed with another opto switch was worth it.

Going to redo the mirrors to fix the problems i mentioned and give it another run with the laser .

Something i found out lego blocks are shiny enough to reflect a laser ,i tried a white block with a red laser and there was a very good reflection any case its a good accurate surface for mirrors.
Heres mark 3 version with the mirrors with self adhesive backing , they are thiner and a lot easier to work with .

I tried double reflecting the white lego there is a light level loss
Attachments
IMG_8975.JPG
lego reflection
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IMG_8978.JPG
The plastic is very shiny surface,not as good as a mirror but not to bad for a laser
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IMG_8979.JPG
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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: Slow Scan Television Experiment

Postby Steve Anderson » Fri Oct 10, 2014 12:35 am

I like SSTV as well as NBTV whatever 'standards' you may apply to either. The original SSTV standard as devised by Copthorne McDonald in the 1950's was a 1:1 aspect ratio frame comprising of 120 lines transmitted in around 7-8 seconds over a telephone/ham radio circuit. Therefore not television in the adopted sense, but a sequence of stills, not that different to facsimile/fax.

That 120 lines in today's binary world has become 128 or a reasonable multiple thereof, with or without colour. None of which particuarly interests me, but well done to those that have expanded on Copthorne's original concept.

Now one item I have on my 'To Do' list is a camera that could generate SSTV pictures, but unlike Harry, I won't be doing it in real time. If you are creating a stil - take your time - my (untried) concept takes just shy of four minutes to scan a live scene, so if it's of a person they'll meed to keep still for that period of time, similar to the Daguerreotype or similar photographic processes of that period.

I did try a couple of years ago to use a pin-hole camera, it sort-of worked, but the noise in the signal was simply too high. With some simple optics this could well be solved, but thus far I haven't got to that stage.

It is mechanical in both axis of scanning, more when I have the time...

Steve A.
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Fri Oct 10, 2014 10:19 am

Yes Steve the original 7 or 8 second SSTV should be kept alive soon as it evolved into colour and other mutant modes it took the shine off the home construction side of things monitor wise .

Its very sad that SSTV still exists but no one ever uses the original system standard ....

I am sort of seeing how it gos here so as aways chop and change it as to what works what doesn't and do my little bit to try and experiment with that standard .

I feel testing the scan with a laser this would be a good starting point and a flying spot camera might be a better option for me trying this for a start .

I recall Steve you mentioning the SSTV camera you were working on i see its still on your mind to give it another go .
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: Slow Scan Television Experiment

Postby Steve Anderson » Sat Oct 11, 2014 11:49 am

Yes Harry, the SSTV mechanical camera is still on my lengthy 'To Do' list. When will I get around to it? Who knows?

Other things are getting priority at the moment, and I still have the 5" CRT monitor/display to do as well as the 625-to-NBTV converter to finish.

But I'll be watching this thread with interest.

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Re: Slow Scan Television Experiment

Postby Harry Dalek » Sat Oct 11, 2014 4:42 pm

Steve Anderson wrote:Yes Harry, the SSTV mechanical camera is still on my lengthy 'To Do' list. When will I get around to it? Who knows?

Other things are getting priority at the moment, and I still have the 5" CRT monitor/display to do as well as the 625-to-NBTV converter to finish.

But I'll be watching this thread with interest.

Steve A.


Yes Steve i think we are all the same have ideas we want to try and hope time allows it one day I know you have a big project on your hands at the moment

Least theres still 2 of us left that like Original SSTV ?.

Today my plan is to mount the laser which is done and get the steppers to move the scan in the right directions my frame scan is the wrong way around.

The large mirror on the line scan arc is a little large it does give a wide scan line even at close distances ,i could drop the size of this one for sure .

Any case i will show a laser scan when i look at the steppers today.
Attachments
IMG_8983.JPG
mounted the laser today
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IMG_8984.JPG
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IMG_8986.JPG
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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: Slow Scan Television Experiment

Postby Harry Dalek » Sat Oct 11, 2014 8:39 pm

Hooked up the all the boards todays first attempt at a correct scan..... frame scan is still to fast need to slow down its timer .

The scans start a bit higher than the book i am using as a screen if looking at the animated gif.

Well its a start i will see if i can tweak its performance.
Attachments
IMG_9004.JPG
first go at a scan
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IMG_9016.JPG
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IMG_9023.JPG
IMG_9023.JPG (334.03 KiB) Viewed 7495 times
MVI_9024 (1).gif
test run
MVI_9024 (1).gif (2.43 MiB) Viewed 7495 times
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: Slow Scan Television Experiment

Postby Harry Dalek » Sat Oct 11, 2014 11:18 pm

Heres some information on SSTV the flying spot pdf i am trying the VCO in that circuit with BC 547 replacements.
Attachments
Flying spot sstv.pdf
(2.03 MiB) Downloaded 309 times
sstv.pdf
Using the clock idea on page 91
(3.41 MiB) Downloaded 290 times
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: Slow Scan Television Experiment

Postby Harry Dalek » Fri Oct 17, 2014 8:00 pm

I am looking at the VCO part,this transistor one ,but testing it so far with a few changes to the circuit ,the diode crossed out as it didn't work with it and the 47k seemed to high with my resistor wheel over the 47k i would say 1k pot here would be a good idea .
Results were negative 12 volts dropped the VCO to around 1500hz and with out jumped right back to 2400hz black to white in other words.

So its voltage sensitive works but needs a 12 volt range,i will keep it and just play around with some others to see out of interest ,need some where to start and hook it up and see the results .

I have only played around of late with the VCO apart from a 555 which pretty much is that if you run it on battery or change just its supply voltage the thing is just voltage sensitive.

I tried a 4046 which i need to look at again as i am not sure i did it right ,that test it worked but was very sluggish there was no instant change but a slow rise and fall with a voltage change to slow to be of any use .

The 555 more than likely a good choice .
Attachments
IMG_9033.JPG
Changes made to the VCO
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IMG_9035.JPG
zero volts
IMG_9035.JPG (390.32 KiB) Viewed 7434 times
IMG_9036.JPG
negative 12 volts
IMG_9036.JPG (417 KiB) Viewed 7434 times
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: Slow Scan Television Experiment

Postby Harry Dalek » Sat Oct 18, 2014 10:18 pm

I started doing rudimentary test on the transistor VCO i have put together .

And so far so good the test is just a manual switching of the negative 12 volts on and off on the voltage controlled oscillator testing the result on MMSTV program.

It does 8 sec slow scan so thats what you see on the screen with time shown in black white stripes how many seconds i switched from 1500 to 2400hz pretty simple but works .

MMSTV has a frequency meter which comes in handy .

I should try a grey scale next then the tricky part getting a head amp to work it .
Attachments
IMG_9037-crop.JPG
manual switching of the black and white frequencies veiwing results on MMSSTV
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IMG_9040.JPG
simple change to the output transistor part
IMG_9040.JPG (350.74 KiB) Viewed 7417 times
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: Slow Scan Television Experiment

Postby Steve Anderson » Sun Oct 19, 2014 3:00 pm

It seems like you're getting there Harry, But I was surprised when you mentioned the slow response of the 4046 a few days back. You only need to use the VCO secion, simply ignore the phase comparators. I did knock one up a few years ago and had no real problems with it. I ran it at 16 times the normal SSTV frequencies (19.2kHz-36.8kHz), this then was fed into a 'walking ring' counter which produced a not-so-bad sine wave. Some simple filtering followed to clean up and remove the harmonics.

I don't have any circuits for it as it was done for amusment more than anything else, a 'see if it's possible' exercise.

I'm somewhat house-bound at the moment, I took a bit of a tumble down some stairs yesterday, so I have the time to have another fiddle with it.

Steve A.
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Sun Oct 19, 2014 10:51 pm

Steve Anderson wrote:It seems like you're getting there Harry, But I was surprised when you mentioned the slow response of the 4046 a few days back. You only need to use the VCO secion, simply ignore the phase comparators. I did knock one up a few years ago and had no real problems with it. I ran it at 16 times the normal SSTV frequencies (19.2kHz-36.8kHz), this then was fed into a 'walking ring' counter which produced a not-so-bad sine wave. Some simple filtering followed to clean up and remove the harmonics.

I don't have any circuits for it as it was done for amusment more than anything else, a 'see if it's possible' exercise.

I'm somewhat house-bound at the moment, I took a bit of a tumble down some stairs yesterday, so I have the time to have another fiddle with it.

Steve A.


Yes Steve i knocked a 4046 together a little while back ,i don't think there was much to the circuit apart from a few added parts 2 resistors and a cap i recall ,my results were it worked but was very slow changing frequency a slow rise and fall i can only think i used the wrong capacitor ,i am pretty sure i did something wrong as it should work faster than that ,i will review this one as it would be a nice handy ic to use .

I hope your ok there ! i went through my garage sky light sheeting trying to help the next door neighbour cut he's over hanging tree branches a few weeks ago lucky for me i landed on my feet like a super hero very lucky .

Heres a OH whoops moment again i liked this sstv vco circuit from the hand book apart from it needed a dual power supply ,i didn't have the FET transistor that is the VCO in the circuit but had a fair in my junk box to try and replace it with ,try as i might could not get it to oscillator right .

Then reviewing an old 73 magazine today i came across the same VCO circuit used in the hand book and was surprised the FET symbol was a Unijunction transistor no wonder i was having problems !

Didn't they have FET transistors in the 70s ? i would say so but why is a Unijunction transistor shown as a FET ?
Attachments
Screen 00009.jpg
Screen 00009.jpg (169.69 KiB) Viewed 7393 times
Screen 00008.jpg
OH its a Unijunction transistor !
Screen 00008.jpg (75.49 KiB) Viewed 7393 times
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: Slow Scan Television Experiment

Postby Steve Anderson » Mon Oct 20, 2014 11:41 am

The circuit (00009.jpg) you posted could be quite easily changed to a single-supply version with a few changes to some of the components.

Somehow, although nice and simple, the unijunction oscillator probably isn't that linear, but better than nothing. If you replaced it with the VCO section of a HEF4046 (not a HC version) you could eliminate the 74LS90 device, this would also remove the requirement for a +5V supply. Though if the rest of the system uses +5V it makes no difference.

There is a 'proper' symbol for a unijunction, I can't recall what it is though, I'll do a Google...OK, found...attached...

Though reading a few datasheets on these devices many manufacturers use a symbol which for all the world looks like a SCR.

I'll have a look at this a little later- I have a few things to do this morning first.

Steve A.
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Re: Slow Scan Television Experiment

Postby Harry Dalek » Mon Oct 20, 2014 4:45 pm

Steve Anderson wrote:The circuit (00009.jpg) you posted could be quite easily changed to a single-supply version with a few changes to some of the components.


I just wanted to see how the circuit worked with out having to think to much about swapping parts ,i had every thing apart from the trouble maker transistor .

Somehow, although nice and simple, the unijunction oscillator probably isn't that linear, but better than nothing.


I still have the circuit so i will see if i can get a unijuction trany looking at jaycar our electronics store they have a 2N2646 , part 2 of the usful sstv circuits from 73 magazine does say best VCO is a Pll ,they say a 565 which i do happen to have 2 or 3 of but as we have talked about the 4046 is a nicer ic.


If you replaced it with the VCO section of a HEF4046 (not a HC version) you could eliminate the 74LS90 device, this would also remove the requirement for a +5V supply. Though if the rest of the system uses +5V it makes no difference.


I have 2 cd4046BCN ?

I will have a look if i have that version of the 4046 handy and then use a single rail opamp instead of that of old 741 once i get around to it this week.

I will still try the transistor one its not giving me any problems any case its near on finished.

I brought a heap of small pcbs instead of large ones as i have change my mind set on best way to make things as in this case i want to drop the size and be able to reuse the circuit with out having other parts of the circuit on the same board which i perhaps would rather replace in time this way it makes it easier.
When i want as in this case a sstv VCO circuit its made /.

There is a 'proper' symbol for a unijunction, I can't recall what it is though, I'll do a Google...OK, found...attached...


My problem was i saw a FET symbol in the circuit i didn't check the transistor as i knew i would not have it just knew i had FET replacements if they put a Unijuction symbol , i would of known from the start ! :roll:

Though reading a few datasheets on these devices many manufacturers use a symbol which for all the world looks like a SCR.


Yes its very strange there must of been a time when some one made up the symbol and some one else didn't know and did the same and in the case of the one looking like a FET they didn't know of FETS by the looks of it either ,i have some old electronics Australia magazines and you would have trouble working out the transistors they look like FETS without the arrow just 3 lines perhaps they are early FETs ? who knows .

I'll have a look at this a little later- I have a few things to do this morning first.

Steve A.


No worries let me know what you find .
Attachments
IMG_9044.JPG
The VCO without the unijuction
IMG_9044.JPG (382.75 KiB) Viewed 7374 times
4046VCO.gif
I will give it a go again
4046VCO.gif (7.55 KiB) Viewed 7370 times
2N2646.pdf
unijuction transistor
(52.5 KiB) Downloaded 368 times
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: Slow Scan Television Experiment

Postby Steve Anderson » Tue Oct 21, 2014 1:16 pm

The values of the components and the output frequencies listed within the 4046 diagram above agree fairly well with the Philips datasheet.

As it shows a 9-12V supply it's a HEF4046 (Philips) or a CD4046 (Motorola & Texas), so your examples should be OK.

I say 'fairly well' as there is an immense spread amongst these devices. This is down to the Silicon process used to fabricate the chips, it's more suited to logic circuits rather than linear ones - which is what the VCO is - linear. For the same reason these devices also have a chronic sensitivity to the supply voltage, it must be regulated otherwise the frequency will be all over the place. Note that pin 15 has a 7.5V Zener for precisely this reason. The HC version doesn't have or need this, a third phase comparator output is present instead.

But if you've got the unijunction version going I would continue with it.

Steve A.
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