NBTV DissectorCam Project, Part 7

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Today's update covers a couple of minor issues discovered in the first phase of camera testing. It is suspected that the deflection is running a little bit below the optimum scan size and there is an issues with the back focal distance of the lens. The latter was not unexpected. Finally we take a mini deep dive of the deflection circuits as they exist in the first revision of the design.
If you enjoy this content, you can find more like it at my web site, Labguy's World. Completed projects, as seen in these videos, are documented there in greater detail than in the videos. Especially when it comes to project details should you decide to make your own copies of my designs.
www.labguysworld.com
Enjoy!

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Опубликовано:

28 июн 2021

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Комментарии : 10

@ShellacScrubber 3 года назад

Thanks for sharing the info' Labguy. It's always interesting to watch the evolution of a project with all it's real world problems and subsequent solutions.

@TeslaTales59 3 года назад

Complex, but interesting!

@videolabguy 3 года назад

Thank you for your confidence. Complex? This is the crystal radio of TV cameras!

@hughgilbert390 3 года назад

What are the yoke inductances? Have you tried to drive with an amplifier similar to LM1875? The line amplifier can easily run out of voltage for retrace.

@videolabguy 3 года назад

Great question! I have not tried the LM1875. Just downloaded the datasheet. Will give it a read. Thanks! The spec's of both coil are the same (X & Y), 50µH, 0.5Ω and a Q of nearly 1. You are correct about retrace time. In this system, the frequencies are so low this is not an issue. I chose this yoke specifically for its near short circuit resistance. This swamps the inductance at all but the highest frequencies I plan to run. The key is to find a fast high current amplifier that is up to the task. If you look closely in the video, you may see a breadboard in the background with an early test circuit in the works. The next reference design I have is the one used in commercial video arcade monitors. 120 watts per channel, going from DC up to about 37Khz bandwidth. Though this may be ideal, it is massive overkill in this situation. I am currently constructing this amp to use with my hand wound torroid deflection coil in the previous project. If I get that working, then we get to delve into pincushion correction circuits. Oh, joy.

@gustavodotgoretkin 2 года назад

I've got a question, and maybe an answer. Because of the choice of feedback, this design produces a current ramp in the yoke coil. The magnetic field strength is proportional to current, so that makes sense. What happens if you try to drive the coil with a voltage ramp, taking the feedback not from the power resistor, but from the output of the drive? If I'm thinking about it correctly, the current would ramp quadratically, which is undesirable.

@videolabguy 2 года назад

Your logic is spot on. Voltage drive and inductors don't play nice together. This is why I use the feedback method shown. However, the 25Ω resistors are the best values I have on hand at the moment. I want to try 10Ω, 15Ω and 20Ω values as well. I just don't have them yet. FYI: The new scan drivers are working exactly like the old ones. The current drain resistors ARE the next thing I will try when I get them. Stay tuned. Also, I have been job hunting and that really cuts into my ability to work on my pet projects.

@039dalekmoore2007 3 года назад

Focus .. bit like the Hubble Telescope least your on earth to fix it ; )

@videolabguy 3 года назад

The difference between Labguy and NASA is I knew this was going to be a problem before I built the camera and planned for it. Build, test, fix. Simple. Same process Elon Musk is using at SpaceX. "The best part is no part." I am pointing out the simplicity of this design. It's one of my unspoken goals.

@039dalekmoore2007 3 года назад

@@videolabguy only joking Richard its always the way see how it go's then next step