Mechanical camera - need advice

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Mechanical camera - need advice

Postby smeezekitty » Thu Jun 27, 2019 8:21 am

So around the time I made the first revision mechanical monitor, I also made a mechanical camera.
Needless to say, it didn't really work.

I'm currently in the process of reworking it to hopefully make it functional. I'm replacing the bearing with a VHS head and 3d printed pullies like I did for the monitor.

In my original design, I used a large CDS cell for a pickup behind the disc. But I think they are too slow for NBTV so I am probably going to need to switch to a phototransistor or PV cell.

My design was not a flying spot but rather but the sensor behind the disc. Has anyone else done it this way? I am concerned about whether enough light will pass through the holes to create a usable signal. Also, what type of lens do I need to use?

I also need to think about whether I need a sensor preamp (maybe an opamp circuit?) and how I am going to generate sync pulses.
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Re: Mechanical camera - need advice

Postby Harry Dalek » Sat Jun 29, 2019 7:39 pm

smeezekitty wrote:So around the time I made the first revision mechanical monitor, I also made a mechanical camera.
Needless to say, it didn't really work.


Try and try again was what i did its a pity Gary is no longer on the forum but he did leave a lot of advice on the forum as it was something of interest to him .

I'm currently in the process of reworking it to hopefully make it functional. I'm replacing the bearing with a VHS head and 3d printed pullies like I did for the monitor.


This is good i think that is a good move ...but the main problem i found was you need to make the device in a light proof box apart from light focused onto the nikpow disk scanning area ...any light getting in from sides such will show up as noise .
Reason i like the pulley vcr head idea is you need that disk steady for your scanning lines ....they will show up ragged in a bad sinewave due to the sync pulses made via a opto switch mechanical way a very sight wobble the disk will make a variable in pulse width thus a ragged video lines not lining up nice and straight ...i cheated here swapping over to a 400 hz crystal made sync mixing that instead of the mechanical sync and got a nice straight lines lining up again .
I used a cd or dvd nipkow using the tiny dc motor they use...... when rotating it looks ok but there is a very slight wobble to the disk fine for the video dreadful for making mechanical sync !

You could just mechanically use the same shaft for the monitor and camera and film the results but i like to make my own video to record and play back as its not that hard and the long run a lot easier really .

In my original design, I used a large CDS cell for a pickup behind the disc. But I think they are too slow for NBTV so I am probably going to need to switch to a phototransistor or PV cell.


Ok i tried photo sensitive resistors for flying spot scanning pick up and photo transistors diodes ...here the problem is lack of surface area ..think of a matrix of leds in the nipkow monitor idea you would sort do this in reverse or has others have done main way a lens to focus it down to the one photo diode bit of a pain really when you can use something else with a larger surface area for light sensitivity of the whole scanning area and do away with that ! a pmt or solar cell ...
i found solar cells have both the surface area and bandwidth ..so solar cells and PMTs are my thing for cameras

My design was not a flying spot but rather but the sensor behind the disc. Has anyone else done it this way? I am concerned about whether enough light will pass through the holes to create a usable signal. Also, what type of lens do I need to use?


Its been done by me and Troy but you will see hes is complex with that lens system ...The arrrr moment for me always was a light proof case that's where i failed at my first go at a direct light camera all the light sensitive devices would work one way or another but you need to keep out all the unwanted light ,i could always tell if i was getting a poor picture with noise on my pmt nipkow camera i had a scratch of paint missing letting light in the case .

I also need to think about whether I need a sensor preamp (maybe an opamp circuit?) and how I am going to generate sync pulses.


Every thing is on the forum to make a camera i will link after some pages i know would be useful to you .
Yes for me its not a camera unless you make a video signal that's my thinking when i do it others may not bother but i like to do it and save my work as video files .
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Re: Mechanical camera - need advice

Postby Harry Dalek » Sat Jun 29, 2019 8:49 pm

Some links to look at for ya

My first go at a camera but flying spot ..if any thing i got some thing out of it with a torch led most use a converted slide projector .
http://www.taswegian.com/NBTV/forum/vie ... solar+cell

PMT nipkow camera used an old video camera lens a 35mm might of been a better idea this ones was giving a tunnel effect .
Did a lot of work on this one ..more know what to do and not do next time
http://www.taswegian.com/NBTV/forum/vie ... a&start=60
http://www.taswegian.com/NBTV/forum/vie ... &start=135
http://www.taswegian.com/NBTV/forum/vie ... &start=375

This page on the mirror camera i tried the arr moment didn't kick in it need to me enclosed all tests open room light idiot move by me...i could see and led infront of the camera didn't sink in i need to enclose the thing for the low light levels ...live and learn !
Any case the experiment showing a solar cell picking up NBTV light and solar cell its self connected to the lap top no other electronic head amps just it to lap top and nbtv player software shows the solar cell has the band width for a camera...
also the light sensitive diode tested but very directional due to the small surface area reason for a camera to need to focus to its tiny surface area .
http://www.taswegian.com/NBTV/forum/vie ... a&start=90
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Re: Mechanical camera - need advice

Postby smeezekitty » Sun Jun 30, 2019 12:25 pm

Thanks Harry!

Try and try again was what i did its a pity Gary is no longer on the forum but he did leave a lot of advice on the forum as it was something of interest to him .

Yeah it is. I still wonder what happened. It might motivate me to tackle working on a viewer program again at least.
This is good i think that is a good move ...but the main problem i found was you need to make the device in a light proof box apart from light focused onto the nikpow disk scanning area ...any light getting in from sides such will show up as noise .

Already ahead of you. The original design camera and monitor are already completely enclosed in wooden boxes. I can put black tape over any gaps if I find them. My dad helped me build the boxes when I first made them at like 12 yo. Good decision in retrospect.

I used a cd or dvd nipkow using the tiny dc motor they use...... when rotating it looks ok but there is a very slight wobble to the disk fine for the video dreadful for making mechanical sync !

The aperture size for a disc is formidably small. I'm using a 12" record (so ~306mm) and even the 1mm holes I'm using are oversized.

You could just mechanically use the same shaft for the monitor and camera and film the results but i like to make my own video to record and play back as its not that hard and the long run a lot easier really .

I'd much rather keep them separate units. It feels like cheating to have them on the same shaft. Besides, that is a lot more difficult mechanically and mechanical design is my weakest.


Ok i tried photo sensitive resistors for flying spot scanning pick up and photo transistors diodes ...here the problem is lack of surface area ..think of a matrix of leds in the nipkow monitor idea you would sort do this in reverse or has others have done main way a lens to focus it down to the one photo diode bit of a pain really when you can use something else with a larger surface area for light sensitivity of the whole scanning area and do away with that ! a pmt or solar cell ...

I am surprised you got this much bandwidth the the photoresistor. My tests showed a very poor response. Surface area isn't a problem though. When I say a large CDS cell, I mean a LARGE CDS cell.
It is the same as the big one in this picture. It is at least 20mm wide.
But maybe that's why the response is so bad. It probably has a lot of capacitance being so large.

I read all the linked threads completely. What a rabbit hole! Looks like I'll have a lot of pain with synchronization and noise. I'm not nearly as picky as Gary was though.
I was honestly tempted just to free run the motor around the right speed and hopefully create sync pulses that are good enough for a stable picture. My disc is large enough and is decoupled from the motor by a belt so that there is little speed variation over the course of one frame. My mechanical monitor only syncs once per frame and it works well.

Apparently my disc is quite thick for a camera but I don't think there is much I can do about that.

It does seem like flying spot cameras are easier to build but they have their own uniqe challenges. Like finding a bright enough light source that won't overheat the disc. Also, it's a bit annoying that they require total darkness. If it doesn't work out with a sensor behind the disc, I might try it.

Lots of good amp circuits in the threads linked. BC109's are not easy to get in America. But I think I can substitute in 2N5088's. They have similar Hfe and noise figures. Somewhat lower current but I shouldn't need to run a lot of current through them anyway.
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Re: Mechanical camera - need advice

Postby Steve Anderson » Sun Jun 30, 2019 2:11 pm

Yes, the 2N5088's are similar in terms of noise to BC109's, but the 2N5089 is 1db better on noise factor, and slightly higher gain, assuming you can get them.

Don't forget to use metal-film resistors, not anything based on Carbon. Clean noise-free power supplies are essential, be wary of the usual 78xx & 79xx series regulators, they can be quite noisy, follow them with a series resistor at the output then a decoupling/bypass cap to mop up most of the rubbish.

Screen all as best you can to eliminate hum pickup.

The above generally only applies to low-level circuits (pre-amps etc.), but is good practice generally.

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Re: Mechanical camera - need advice

Postby Steve Anderson » Sun Jun 30, 2019 2:43 pm

The ultimate in low noise from that era is the LM194/394. Two super-beta transistors only in an 8-pin DIL package. Almost impossible to get now and hideously expensive. An alternative is the SSM22xx series, similar idea. (SSM2210, SSM2212 & SSM2220). Note the SSM2220 is two PNP devices, the rest are all NPN.

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Re: Mechanical camera - need advice

Postby Harry Dalek » Sun Jun 30, 2019 7:07 pm

smeezekitty wrote:Yeah it is. I still wonder what happened. It might motivate me to tackle working on a viewer program again at least.


Very sorry to loose Gary here...hope he's doing well up in the southern highlands of NSW, he was a mechanical television Sensei and like you able to turn that into software as well ....
I think he's software is scattered about but not in one place here on the forum ...Since the web site is gone we should put it on a page here ..there's a bit of NBTV software about The big picture viewer served us well ..
A multi system viewer would be great there's few that can do this so it would be a good thing ....i am a big fan of FreeNBTV a viewer would top it off !

Already ahead of you. The original design camera and monitor are already completely enclosed in wooden boxes. I can put black tape over any gaps if I find them. My dad helped me build the boxes when I first made them at like 12 yo. Good decision in retrospect.

This is a good skill to have a pat on the back for your dad .


The aperture size for a disc is formidably small. I'm using a 12" record (so ~306mm) and even the 1mm holes I'm using are oversized.

Well its had to get the correct Aperture size on a cd size bit easier record size but possible close enough to still get it to work ...
I used paper encoder printed out and stuck on my cd nipkow so it was a reflective method IR led sensor to make the mechanical sync and for motor control ..the wobble of the disk was very very small but enough to vary the sync pulse ....the wobble was due to the mount to motor shaft it didn't have to be that accurate for what it was made for but not so good a flaw for a mechanical camera design ...The video head and mount are dead on made it not to wobble so you should have better luck more accurate sync pulses with correct pulse widths one after the other ..the encoder disk holes what ever you use have to be accurate or image will be flawed ..

I'd much rather keep them separate units. It feels like cheating to have them on the same shaft. Besides, that is a lot more difficult mechanically and mechanical design is my weakest.


Yes its not my thing either agree here .


I am surprised you got this much bandwidth the the photoresistor. My tests showed a very poor response. Surface area isn't a problem though. When I say a large CDS cell, I mean a LARGE CDS cell.


I only used it at the start of the flying spot idea and gave up on them but they are yes sluggish solar cells are much better idea .

It is the same as the big one in this picture. It is at least 20mm wide.
But maybe that's why the response is so bad. It probably has a lot of capacitance being so large.[/quote]

More than likely worse bigger they get but as you know better light sensitive devices out there .

I read all the linked threads completely. What a rabbit hole! Looks like I'll have a lot of pain with synchronization and noise. I'm not nearly as picky as Gary was though.
I was honestly tempted just to free run the motor around the right speed and hopefully create sync pulses that are good enough for a stable picture. My disc is large enough and is decoupled from the motor by a belt so that there is little speed variation over the course of one frame. My mechanical monitor only syncs once per frame and it works well.


Funny enough you can get pretty close to correct speed free running but it will always drift above or below wanted set point ...if 32 line 400hz i used that free soundcard scope1.32 program on the below screen to view the sync and checking how well the motor is controlling speed .
download.jpg
download.jpg (36.51 KiB) Viewed 3428 times

Really need good motor control as it will go out of sync and be very annoying ! pain to record too ....view the speed on that software feed the sync to the sound card and if it is stable fine .

Apparently my disc is quite thick for a camera but I don't think there is much I can do about that.


harder to wobble i like that !

It does seem like flying spot cameras are easier to build but they have their own uniqe challenges. Like finding a bright enough light source that won't overheat the disc. Also, it's a bit annoying that they require total darkness. If it doesn't work out with a sensor behind the disc, I might try it.


I made my flying spot camera with one luxeon and the thing was not even enclosed wasting light causing noise i still manage to get an image ...if you read the first link on the flying spot camera i started with a out with the luxeon torch then switched to a out of focus green laser behind the nipkow till i broke it ! then back to the luxeon
http://www.taswegian.com/NBTV/forum/vie ... &start=135
So heat is not a problem just most people tended to use a converted slide projector i had other ideas .

Lots of good amp circuits in the threads linked. BC109's are not easy to get in America. But I think I can substitute in 2N5088's. They have similar Hfe and noise figures. Somewhat lower current but I shouldn't need to run a lot of current through them anyway.
[/quote]

Yes lots of head amp circuits lots of trany versions i like the ne5534 the trany circuits can be touchy to get right but fun to experiment and see what works for you .
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Re: Mechanical camera - need advice

Postby smeezekitty » Wed Jul 03, 2019 4:49 am

I have the disc assembly mostly finished
20190701_200530_resized.jpg


And I got an image! Just connecting the CDS cell to a single 2N2222 amp and focusing a lamp onto the disc with a magnifying glass.
You can make out the curved filament.
filament_pic2.bmp
(37.55 KiB) Downloaded 103 times


Obviously still a lot of work to do
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Re: Mechanical camera - need advice

Postby Harry Dalek » Wed Jul 03, 2019 6:07 pm

Great result for the light sensitive resistor,you can use what you made as a test bed for other photo sensitive devices and see what works best for you .
Once you get to the reflective light off an object is where the fun starts ...simple test cards ,toys make good stooky bills ; )
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Re: Mechanical camera - need advice

Postby smeezekitty » Fri Jul 05, 2019 10:53 am

I thought I had some 2N5088 in the parts box but I couldn't find them.

In the mean time, I added a reed switch and magnet (like I used on the monitor) to generate a frame pulse. I recorded the frame pulse on the right channel and the video on the left channel.

Inspired by Gary's work, I knocked together a timebase correction program that would correct the video based on the frame pulses. It actually works surprisingly well and yields a stable picture in TBP

Here I was holding a piece of plastic with an "X" written on it between the light and camera lens:
https://www.youtube.com/watch?v=SdiIMNKJ8oo
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Re: Mechanical camera - need advice

Postby Harry Dalek » Fri Jul 05, 2019 10:44 pm

smeezekitty wrote:I thought I had some 2N5088 in the parts box but I couldn't find them.


Always the way can never find some thing when you want it

In the mean time, I added a reed switch and magnet (like I used on the monitor) to generate a frame pulse. I recorded the frame pulse on the right channel and the video on the left channel.


I did something similar with Hall effect sensors but for line sync ..any case good thinking .

Inspired by Gary's work, I knocked together a timebase correction program that would correct the video based on the frame pulses. It actually works surprisingly well and yields a stable picture in TBP

Here you have one up on every one not computer programming savvy ...looking at your youtube video works very well .
You should see if you can do it all mechanically and get a stable picture to record via and taming that motor you will find if your recording plays stable on DOM's player software you have done it ...it has to be correct to play in sync no software help via Garys Big picture for sync that's a touch off it has to be 100% correct .. i used that for my mechanical cameras to test their operation in correct speed so very good software for testing your motor speed ...it can't be 399hz 401hz has to be 400 hz .

Here I was holding a piece of plastic with an "X" written on it between the light and camera lens:
https://www.youtube.com/watch?v=SdiIMNKJ8oo


Movement is very good for seeing results ...
ON what i see is a problem is lack of surface area of the light sensitive resistor thus the light gaps top and bottom of scan might help a larger light in front or focusing behind the disk scan to the LDR's smaller area ,you also have a noise problem from the motor from the brushes ...perhaps try some caps from motor positive to ground ,the motor might be a bit worn ...Keep going doing well its good experimenting .
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Re: Mechanical camera - need advice

Postby smeezekitty » Sat Jul 06, 2019 2:49 pm

Steve Anderson wrote:Yes, the 2N5088's are similar in terms of noise to BC109's, but the 2N5089 is 1db better on noise factor, and slightly higher gain, assuming you can get them.

Don't forget to use metal-film resistors, not anything based on Carbon. Clean noise-free power supplies are essential, be wary of the usual 78xx & 79xx series regulators, they can be quite noisy, follow them with a series resistor at the output then a decoupling/bypass cap to mop up most of the rubbish.

Screen all as best you can to eliminate hum pickup.

The above generally only applies to low-level circuits (pre-amps etc.), but is good practice generally.

Steve A.

I'm definitely see noise problems. I am using lab power supplies which are pretty clean and putting bypass caps but I think I'm getting burned by long leads.

The ultimate in low noise from that era is the LM194/394. Two super-beta transistors only in an 8-pin DIL package. Almost impossible to get now and hideously expensive. An alternative is the SSM22xx series, similar idea. (SSM2210, SSM2212 & SSM2220). Note the SSM2220 is two PNP devices, the rest are all NPN.

I have enough external noise sources to worry about, I'm not really worried about a 3db noise figure transistor.


Yes lots of head amp circuits lots of trany versions i like the ne5534 the trany circuits can be touchy to get right but fun to experiment and see what works for you .

I thought I had an appropriate transistor which is why I wanted to use that at first. I'll try several options until one works well


ON what i see is a problem is lack of surface area of the light sensitive resistor thus the light gaps top and bottom of scan might help a larger light in front or focusing behind the disk scan to the LDR's smaller area ,you also have a noise problem from the motor from the brushes ...perhaps try some caps from motor positive to ground ,the motor might be a bit worn ...Keep going doing well its good experimenting .

You're right. I changed the orientation of the cell and it covers more area but still not all of it. I'll need to rethink.
And brush noise is becoming a real pain in the behind. I put a cap across the motor and it knocked it down but it's still not noise free.

Once you get to the reflective light off an object is where the fun starts ...simple test cards ,toys make good stooky bills ; )

I found a 600W halogen movie lamp and with it, I can use it as a real camera and reflect off of test cards and things.

While I'm waiting for parts and I need to make a new Nipkow disc (this one has an obvious defect down the center), I have been working on more software post processing.
I know some people might consider it "cheating" but I feel that it is all part of experimentation.

I wrote another utility that would do DC restoration and add NBTVA syncs to it. Now the signal is nearly to NBTVA spec and it plays well in TBP and NBSCPlayer with syncs enabled.
I can also now play it back on my mechanical monitor -- although it is not locking on to the sync that well. I'll need to figure out if it is a signal problem or if the monitor needs maintenance.
20190705_135909.jpg
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Re: Mechanical camera - need advice

Postby Harry Dalek » Sat Jul 06, 2019 9:36 pm

Hi it might need a lot of light but camera it is .....you can only do what has happened in this next video here and that's improvement which i can see !

Pity about the motor noise brushes might be to warn out to much ...which there's only one fix and that's a replacement pain as it is ...that's if you can be bothered it doesn't stop it displaying ...perhaps some thing for the next camera .

The wav file plays well on Big picture but will not load on big picture v2 unless you use the chris long setting then its only half a frame ...always had trouble with V2 displaying correctly at times have not tried it on Doms software yet ...

More light is good ...i would as you are doing tinker and see what works what improves it .
some circuits below ..the sstv one used a photo transistor notice the light sensitive area is small i had to follow the scan down the scopes crt screen as it was painting the image the photo transistors pick up is very narrow with out optics....There was a transparent test card over the scopes screen.
Attachments
phototransistors.pdf
might help once you get to those
(62.92 KiB) Downloaded 53 times
kit31.gif
its sensor is like a tiny solar cell i have one of these
kit31.gif (5.21 KiB) Viewed 3163 times
IMG_9128-crop.JPG
it was a bit voltage sensitive used this for sstv feeding the signal to a 4046
IMG_9128-crop.JPG (149.2 KiB) Viewed 3163 times
1 00020.jpg
result of flying spot sstv scanning 5534 circuit above
1 00020.jpg (64.5 KiB) Viewed 3162 times
PhotodiodeAmplifierSchematic.gif
Leds have some photo sensitivity which is just out of interest also old transistors were painted remove back to a clear case they are then light sensitive
PhotodiodeAmplifierSchematic.gif (8.62 KiB) Viewed 3161 times
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Re: Mechanical camera - need advice

Postby smeezekitty » Sun Jul 07, 2019 4:47 am

Harry Dalek wrote:Pity about the motor noise brushes might be to warn out to much ...which there's only one fix and that's a replacement pain as it is ...that's if you can be bothered it doesn't stop it displaying ...perhaps some thing for the next camera .

Yeah it might be. It's a used motor. When I put it all together, I'm going to run shielded leads to the light sensor and build the headamp in a metal box. Hopefully that will help.
The wav file plays well on Big picture but will not load on big picture v2 unless you use the chris long setting then its only half a frame ...always had trouble with V2 displaying correctly at times have not tried it on Doms software yet ...

Yeah TBP has a weird bug about picky super picky about the .wav files. But there is a workaround:
Load a .wav file that is known to be in the correct format first (easiest way is to load something produced my video2nbtv)
Click capture. Then stop it.
*Then* load the .wav file that wasn't working before. Now it should work.

some circuits below ..the sstv one used a photo transistor notice the light sensitive area is small i had to follow the scan down the scopes crt screen as it was painting the image the photo transistors pick up is very narrow with out optics....There was a transparent test card over the scopes screen.

Awesome, Thanks!

I was thinking; since we use an LED array behind a defuser for mechanical displays, why can't one do the opposite for a mechanical camera. That is, have an array of phototransistors in parallel behind a defuser?
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Re: Mechanical camera - need advice

Postby Harry Dalek » Sun Jul 07, 2019 9:30 am

smeezekitty wrote:
Harry Dalek wrote:

I was thinking; since we use an LED array behind a defuser for mechanical displays, why can't one do the opposite for a mechanical camera. That is, have an array of phototransistors in parallel behind a defuser?


That had crossed my mind as well and i can't say i have heard of any one trying it out ,i would think it would work apart from any problems hooking them up in parallel or series,only thing its easier to just use a small solar cell sensitive enough have the bandwidth ..they have the surface area size spot on for a nipkow disk scan ...found in toys ,solar lights or buy new .
i haven't tried a single photo transistor in a nipkow just sstv tv camera scanning i just know you need to focus the scan down to its surface ...try to avoid optics part as much as a can .
viewtopic.php?f=23&t=1890&start=120

viewtopic.php?f=23&t=1890&start=150
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