Physical Limits

[pixeldrift]

I know most folks are probably focusing on historic standards like the 30 and 32 line screens, but I'm wondering about how far the mechanical display technology could be pushed based on physical limitations.

According to my calculations, I could get a 3.5 inch wide display from a 2ft disc. This is with the screen at the top of the disc rather than the side so scan lines are going horizontally across the image and a landscape oriented image of 160x90. Because our eyes are side by side so horizontal resolution matters more, and 160x90 would be a convenient multiple of the 16x9 standard. This would be accomplished by an overlapping spiral of dots on the Nipkow disc with a second spinning disc as a mask to occlude the ones not being scanned for that rotation.

It seems like the main limitation is how fast an LED light source can flash per second. Does anyone have an idea of the refresh rate they're capable of? A simple on/off wouldn't be so difficult, but pulse width modulation to vary the brightness doesn't seem like it would be practical in this application because of the speed?

[Steve Anderson]

Hi, there's no problem with the response speed of LEDs being modulated by PWM or in a linear manner. Steve O (username Panrock) built a colour disc monitor using Luxeons modulated by PWM at 100kHz. It easily could have been much more. A Luxeon is just a glorified LED.

Opto-couplers using IR LEDs can transfer at MHz rates. It's no different for visible LEDs. EXCEPT the 'white' ones which use a phosphor to generate the blue part of the spectrum. This is slow. But there's no harm in trying, maybe improvements have been made in this respect?

Steve A.

[pixeldrift]

That's great to know, the information I was finding online seemed to indicate that LED response time was an order of magnitude lower than that. Fine for simple "on and off" pixels but not fast enough for a period of 255 per dot times 172800 pixels each second! And that's only at 12fps. Hopefully my information was incorrect.

But I did find this documentation which seems to be useful and probably what I'll be needing to study up on once I get to that phase.
https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM
http://playground.arduino.cc/Code/PwmFrequency

I'm putting together a spreadsheet with the variables that will automatically calculate things like disc radius, refresh rate, etc based on inputs such as lines, fps, and physical size. When I've figured all that up I'll share the link. Would love a second opinion on the math.

[DrZarkov]

With rotating or vibrating mirrors and LEDs you can reach very much higher resolution, like HD or even UHD. That's exactly how DLP video-projectors are working. Mechanical TV is again cutting edge technology.