Back in the Game!

[Ralph]

Back in 2005 I had finished two NBTV projects - my ROMScanner image source which contained NBTV still images in EEPROM, and my Virtual Televisor which permitted display of good-sized NBTV images on a PC. I was closing up my lab at the University and visualizing a placid retirement that would provide ample time for NBTV and vintage radio projects. Little did I realize that I would be serving additional years as department Head - where the pace of life does not admit the possibility of outside creative projects.

Now, still not retired, but relieved of the burdens of an administrator, I have warmed up by building a vintage amateur radio transmitter and now it is once again time time for vintage television.

(1) The first thing I did was to restart my NBTV website:

http://taggart.glg.msu.edu/nbtv/nbtv.htm

(2) Next I dug out the Virtual Televisor, which was used for virtually all the NBTV images on the website. That turned out to be a wasted effort as none of my computers will run the software which was developed in a DOS environment. That is a small matter as Gary's Big Picture doesn't need an interface and is designed for Windows!

(3) Found the ROMScanner and it faithfully generates images just like it used to! I also found my club NBTV disks.

My next project "back in the day" was going to be a classic Nipkow-disc televisor and I managed to locate the critical pieces of that project including my 32-line Yanczer disc, the DC motor, and all my custom circuit boards.

I was smart enough to keep my membership up-to-date so have been able to follow the creativity of other members of the Club. A Nipkow-disc monitor is very basic, but this one, when finished, will have some features of interest. Thank you all for the continuous inspiration.

Ralph

[Steve Anderson]

Welcome back Ralph,

I note you said, "My next project "back in the day" was going to be a classic Nipkow-disc televisor...". Is that still the case or have you something else in mind these days?

Looking forward to whatever input you can make here...

Steve A.

[Ralph]

Steve,

Lots of ideas piling up in the project notebook. That said, I have all of these Nipkow components that have been sitting on top of the bookcase for too many years now. If I were to covert them into a working televisor, my wife might be persuaded that I an really serious about reorganizing my den!

Cheers,

Ralph

[AncientBrit]

Welcome back Ralph.

I look forward to seeing your project results here and in the Newsletter.
I've been re-visiting my original Nipkow disc camera and adding some improvements.

Kind regards,

Graham

[Ralph]

Now that the Club Shop has a mirror screw kit, I will simply hide all the Nipkow bits from my loving wife and build a mirror screw. I am going to structure the electronics support package so it would support either televisor.

What is curious is that I can fine some very fine photographs of images from virtually every kind of display except the mirror screw. Most of the mirror-screw display images I have found are not of very high quality. Is there a particular challenge in photographing such a display?

Ralph

[M3DVQ]

Hi Ralph, I thought I recognised your avatar... I have your ARRL book on my shelf here

[M3DVQ]

I find that it's harder to get a good photo of a mirror screw display because of how much brighter the images produced are. This sounds backwards but to get a decent photo off a nipkow a fairly long exposure seems to work well (provided the display is well locked to the sync!)

I find that with a mirror screw I can't get a long enough exposure to catch the image without stopping down so far that the machine is lost in the grainy shadows. My camera though decent is only a compact digital one though so perhaps I'm up against the limitations of the equipment.

[Klaas Robers]

Ralph, it might be that automatic cameras have a problem with their auto focus. The virtual image of a mirror screw has a different distance to you as a viewer in the horizontal direction and in the vertical direction.

This is easily understood as in the direction parallel to the rotation spindle the sharpness is at the distance of the mirror. There are the different lines generated.

However perpendicular to the spindle, that is parallel to the mirrors, the sharpness is at the distance of the line light source, reflected in the mirrors. That is much further away.

I can understand that a camera with autofocus has problems with that in producing a sharp picture. I have the impression as well that our two eyes have a problem with it, especially when the mirror screw is used to display a picture with horizontal lines (vertical spindle). That is even more cumbersome than making a photograph (or viewing with one eye). The verical line BAIRD system offers a certain advantage, as long as you don't tilt your head........

Until now I never had the posibility to experience the pictures of a mirror screw myself. But we have a guy here in NL that made one, hopefully I can see his contraption working soon. Then tilting my head is one of the first things I will be doing.

And then, you are looking into a mirror. This reflects all lighting in the room, which will spoil your contrast.

[Ralph]

Some very good points Klaas! I have much grinding, polishing, and assembly to do (I have the Club mirror-screw kit), but can think of a few things I will try once it becomes operational.

Right now I am building a generic controller which should be readily adaptable to any display system using LED's and a DC motor. I will be using your ingenious one-transistor driver circuit. I have a Daily Express Nipkow unit on the bench that I have equipped with one of Peter Yanczer's 32-line disks which should serve to to check out the controller. Perhaps the mirror-screw mechanics will be done by the time I have the Daily Express mechanics up and running.

Cheers,

Ralph

[Viewmaster]

Some very good points Klaas! I have much grinding, polishing, and assembly to do (I have the Club mirror-screw kit), but can think of a few things I will try once it becomes operational.
Ralph

Ralph, the assembly is critical. I don't know if the club's kit has any features to help alignment.
The angular displacement between each mirror slat must be exact else you will have wavy straight lines on the final picture.
It is well worth spending time on working out a way to get this right.

Indexing pins have been used or shining a narrow slit of light onto a wall. I have used a 64 tooth gear indexing off every other tooth, each slat being clamped to the previous with 32 tiny clamps that I made.

Also be very careful when adjusting one slat that you don't inadvertently move those already adjusted.
Good luck.

[Panrock]

Albert makes some very good points, in particular his final one. The angle setting is really critical, and the more the lines - the worse it gets! I spent an evening recently going through mine with a laser reflecting onto a far wall. This proved time well spent.

Polishing the slat surfaces needs to be done properly too...

I haven't seen the 'club' mirror screw kit yet but hope to get a peek at the forthcoming convention.

Steve O

[Ralph]

Fired up the LED cluster in the replica neon tube for the Daily Express televisor last night. Nice bright amber source, but there is an issue with respect to Klaas's one-transistor driver. The gamma correction resistor in the circuit is 5.6 ohms, based on a peak LED current of 100 mA, using 8- amber or 10-white LEDs. In designing the Daily Express kit, Dennis used a total of 21 amber LEDs. For equivalent brightness from each LED, it looks like the DE LED cluster is going to need ~260 mA compared to the 8-LED amber cluster that needs a peak value of 100 mA. This would suggest that the 5.6 ohm resistor is going to have to be changed.

Klaas, I wonder if you still have your Excel spread-sheet for a quick pass at an alternative value? I can always disassemble the replica neon and substitute an LED cluster appropriate for 100 mA of peak current, which would contribute to a "standardization" of sorts.

Ralph

[Klaas Robers]

Ralph, you can easily place more LEDs in series. Then the supply voltage should be higher as well.

If you use amber 5mm ultra bright LEDs, the ones that can have 50 mA, then make two identical chains, e.g. both 20 LEDs. Place the chains in parallel and the max. current should be 100 mA.

Each LED wil drop a voltage of about 3 volt at 50 mA. So the 10 LEDs will drop 30 volt. Then the BUZ11 needs about 10 volt, so you need min. 40 volt supply voltage. It may be higher, the remainder is over the FET.

For a current of 250 mA the resistor should be about 2.0 ohm for an optimal fitting gamma.

[Ralph]

Thanks Klaas! I have decided to use a 3 x 4 array of 12 ultra-bright white LEDs arranged in six parallel series of pairs. That way I can use the 20V supply I have already fitted and the operating current should be about 120 mA. That will certainly be close enough to the 100 mA figure to permit the use of the 5.6-ohm resistor for initial tests. I can optimize it later if needed.

All the bits and pieces are on order and some have already arrived. My wife will be visiting friends in Florida next week, so a couple of long sessions at the workbench should yield significant progress.

Ralph

[Ralph]

My primary intention with the Nipkow televisor is to use it for demonstrations at club meetings and conventions. Unfortunately, the DE Televisor, while suitably historic, is poorly designed for even its modest price point! I am reconfiguring some of the components to operate (much like the original) to the Club's 32-line standard. All of the fine work that Denis put into the kit is being preserved to the unit can be converted back to stock condition for static museum display at some point in the future.

Here are the towers and new, direct-drive motor mounted on a new base with one of Peter Yanczer's 12-inch discs. Th control unit is only partially done, but preliminary run-up shows a fine raster!

Ralph