Mechanical SSTV Steps

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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Postby gary » Thu Mar 21, 2013 10:44 pm

> the problem of using higher laser levels without wiping the written raster lines from the laser glow

I assume the laser has a collimator?
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Postby Harry Dalek » Thu Mar 21, 2013 11:00 pm

gary wrote:> the problem of using higher laser levels without wiping the written raster lines from the laser glow

I assume the laser has a collimator?


An adjustable lens ?

The higher the laser level it is sort of similar to a CRT you can only make it so bright i need a contrast control but i know the glow from the laser being very bright causes a problem at higher laser levels this UV light is seen by other parts of the drum.
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P1040979.JPG
the adjusted laser ; )
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Postby gary » Fri Mar 22, 2013 10:09 am

harry dalek wrote:
An adjustable lens ?

The higher the laser level it is sort of similar to a CRT you can only make it so bright i need a contrast control but i know the glow from the laser being very bright causes a problem at higher laser levels this UV light is seen by other parts of the drum.


Well the spherical aberration you are seeing at high levels is always there, just not as noticeable because it is not as bright.

Yes I suppose a collimator is just a lens, but for good collimation it should not be of the common spherical kind - however I fear the correct (aspherical) kind to use would be outside your budget. The difference between the two can be quite remarkable (see image).

I think multi element lens collimators are better in this regard as well but probably even more expensive.

I was just asking really to make sure there was a collimator of any kind being used as obviously without one the situation would be even worse.

This is way out of my knowledge and experience now but it may be well worth trolling (in the fishing sense) some of the laser communication sites as they would probably need good collimation.

PS: Come to think of it the laser in a laser printer must have good collimation I would have thought - perhaps that's worth looking at as a cheap source.
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Postby Harry Dalek » Fri Mar 22, 2013 1:17 pm

Hi Gary

Well the spherical aberration you are seeing at high levels is always there, just not as noticeable because it is not as bright.


Yes i understand now i can see that when i just stop the motors and the laser is adjusted looks just like that picture to the eye ...

Yes you are right depending on the laser level the outer ring size just gets brighter ,i am thinking a long mask with a long slit the laser always writes the line to the same line area just the drum screen moves so might help.

Yes I suppose a collimator is just a lens, but for good collimation it should not be of the common spherical kind - however I fear the correct (aspherical) kind to use would be outside your budget. The difference between the two can be quite remarkable (see image).


My other laser the lens is much smaller this one is rather large....i need to look into fixing the problem ..

I think multi element lens collimators are better in this regard as well but probably even more expensive.


Pretty sure the other laser has 2 this one only one large.

I was just asking really to make sure there was a collimator of any kind being used as obviously without one the situation would be even worse.


i am glad you have pointed it out its something i can test for .


This is way out of my knowledge and experience now but it may be well worth trolling (in the fishing sense) some of the laser communication sites as they would probably need good collimation.


I will have a google and see but i am sort of stuck with what i have got handy .

PS: Come to think of it the laser in a laser printer must have good collimation I would have thought - perhaps that's worth looking at as a cheap source.
[/quote]


As i recall it uses a long flat lens well the 2 have pulled apart have might have one handy still in my lens box to test .
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Postby AncientBrit » Fri Mar 22, 2013 6:19 pm

Harry,

Just an off the wall idea.

Are the colours from the laser and the drum fluorescence widely separated in wavelength?

If they are you might be able to insert a coloured filter in the viewing path only.
This would attenuate the direct laser feed but hopefully pass the output from the drum.

Kind regards,

Graham
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Postby gary » Fri Mar 22, 2013 6:26 pm

But isn't the problem that the "over spray" from the laser dot is exciting the fluorescence of the previous lines?
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Postby Harry Dalek » Fri Mar 22, 2013 9:06 pm

AncientBrit wrote:Harry,

Just an off the wall idea.

Are the colours from the laser and the drum fluorescence widely separated in wavelength?

If they are you might be able to insert a coloured filter in the viewing path only.
This would attenuate the direct laser feed but hopefully pass the output from the drum.

Kind regards,

Graham


Hi Graham

I think the problem at high laser levels there is a spill of light as you see in this photo...
I recall being told and reading they used to use yellow filters on the p7 crts for sstv.
But again the scattered light even reflecting back off the sides of the polygon then back to the drum is a problem ...i think a mask would help at higher laser levels.
I am finding this now working very interesting .i will post todays photos next post.
Attachments
P1050008.JPG
P1050008.JPG (164.98 KiB) Viewed 8492 times
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Postby Harry Dalek » Fri Mar 22, 2013 9:14 pm

gary wrote:But isn't the problem that the "over spray" from the laser dot is exciting the fluorescence of the previous lines?
]But isn't the problem that the

Yes gary have a look at this video my camera can not show the sharp dot but the spill of light and reflections show up well.
Attachments
P1050008.mpg
the drums working very slow to show the high laser problem
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Postby gary » Fri Mar 22, 2013 9:25 pm

Harry it's really hard to tell by video but I would swear that there is diffusion through the surface of the drum - if not then the mirror drum is spreading the light - what happens if you shine the laser directly on the drum?
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Postby Harry Dalek » Fri Mar 22, 2013 9:51 pm

Well today i swapped the inputs to the Lm311 for the PWM circuit and so have the right inverted video but now the video is wrong via the polygon rotation direction see felix writing .....my circuit for the steppers is pretty simple i didn't put in a motor reverse so i might have to just turn the motor around so the mirror is going in the other direction..... :oops:

I also worked out my speed for a full screen drum so as in NBTV slow half speed pictures half number of lines i suppose are displayed ...looking at the pictures you can see its getting better getting there .

Now i see it full screen....... the polygons clock could do with a sync pulse from the video it does roll side ways very very slowly one frame at a time roll...still running both drums in manual control ...
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P1050009.JPG
Just working out speed have the large drum to fast
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P1050033.JPG
first human test crazy man face
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P1050024.JPG
Felix the cat
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P1050027.JPG
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Postby Harry Dalek » Fri Mar 22, 2013 10:04 pm

gary wrote:Harry it's really hard to tell by video but I would swear that there is diffusion through the surface of the drum - if not then the mirror drum is spreading the light - what happens if you shine the laser directly on the drum?



Slow and higher power it doesn't look good via this camera
i can see looking at it at this speed even the sides of the mirror are shiny its reflecting back to the drum...could do with black paint the sides ...

Also what we were talking about last time due to this simple lens on this laser due to the focal point which is the distance of the glow drum..... the polygon isn't ! so theres a bit of spill over from a round dot (it isn't focused to the polygon)... wasted light on the polygons mirror faces spilling over the side a touch.
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Postby Harry Dalek » Sun Mar 24, 2013 10:12 am

Last night i changed the stepper motor direction but due to motor i am not happy with where i had to place it ,its directly under the drum so hard to see to sync as its paint the image.
I think i will look into working on a stepper motor direction circuit.
I also have been looking into casing it again every thing seems to fit in the new drum direction position .

Heres a close up of the polygon mirror in the new position you can see if the laser over shoots the mirror theres a bit it can reflect back so thinking about it if i don't use another laser it might be best to place the laser as close to the polygon as, the not so focused dot is kept on the mirror face then.
Attachments
P1050038.JPG
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P1050037.JPG
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1.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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Postby Harry Dalek » Thu Mar 28, 2013 12:24 am

Well i have swapped back to the normal or last good position for the Polygon.
I also have reversed the pin connections for the polygon stepper motor so its going in the right direction.

I tried to sync the motor but seeing what the polygons 555 timer clock was running at 474hz makes it not as easy.

Heres todays pictures not to much improved best i can do will my low laser level adjustments at the moment .
Attachments
P1050041.JPG
Bad framing but every thing is in the right direction now
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P1050078.JPG
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P1050079.JPG
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P1050084.JPG
bit of gray scale need to increase laser level but
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P1050075.JPG
Our hero on mechanical SSTV for the first time ever i wonder if he would be pleased
P1050075.JPG (446.97 KiB) Viewed 8455 times
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Postby aussie_bloke » Sat Mar 30, 2013 10:24 am

Great work Harry, awesome to see pictures on your mechanical SSTV, they are looking good!!! :D
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Postby Harry Dalek » Sat Mar 30, 2013 5:49 pm

aussie_bloke wrote:Great work Harry, awesome to see pictures on your mechanical SSTV, they are looking good!!! :D



Thanks troy

It was a long time coming i want to be able to increase the laser level without washing out the video ,i have Asked Steve for some advice before i get the soldering iron out again .

Its very hard to take a video at the moment its to dark for the camera on movie mode ..... i tried to enhance the video but some players i found it would look like a reversed video and i am sure for those interested would like to see it running.

So i hope i don't get into trouble for a animated Gif but it came out best doing this ,,,,if its a problem i will take it off i suppose i would just have to increase the picture size then again i am not sure they play well large.
Attachments
felix2.gif
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P1050076.JPG
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P1050054.JPG
Test card test
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P1050060.JPG
Vampira
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P1050061.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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