[bitluni]’s laser-based display pretending to be a an old-school vector CRT.Phosphor-based displays like CRTs rely on the phosphor to emit light for a set amount of time after being activated, allowing them to display a seemingly persistent image with one drawing beam per color. Translated to UV-sensitive PLA filament, this means that you can totally use a printed sheet of this material in combination with a 405 nm laser diode to create a display that doesn’t look dissimilar to an early CRT. This is exactly what [bitluni] did in a recent video, meshing together said laser diode, UV-sensitive PLA, stepper motors and two mirrors with an Arduino-based controller to create a rather interesting vector display.
In the video, [bitluni] goes over the development steps, including a range of improvements like being able to turn off the laser when moving between the end of a line and the beginning of a new one. While the Arduino Nano board does the driving of the stepper motor controllers, an ESP32 provides the drawing instructions. The STL and other project files including Nano & ESP32 firmware can be found on the GitHub project page.
While far from being a practical display with a single-digit Hz refresh rate, it does provide an interesting demonstration of these types of persistence of vision based displays, and without the use of exotic MEMS mirror modules or the like.
22 thoughts on “A Laser With Mirrors Makes A CRT-like Display”
Ooh. Now I want to make a SSTV display like this, mimicking the olde P7 phosphor CRTs.
If they had high-quality full color lasers and galvos back then, they probably would have never bothered with the whole vacuum thing. But it sure is a lot easier to quickly steer a charged particle
Thing is, they used vacuum tubes to figure out what electrons and atoms were, so one kinda follows the other – can’t get a laser diode before you build a cathode ray tube.
I think that laser tubes are nice. Their light does sparkle so nicely and they have power.
Laser diodes are primitive, I think. They cheat by stimulating a crystal. And they must pulse for any meaningful output.
It’s like with the “white” LEDs that are actually blue with a white filter.
Still, laser diodes are fine for laser pointers and optical drives.
Calling phosphors a filter is more than a bit wrong, and calling direct stimulation a “cheat” isn’t any better, but I agree laser tubes have a bit more “romance” to them.
Hi, I meant to say that LED bulbs use a white filter (frozen glass etc) to create the illusion of being a white light source. In reality, they’re more blueish by nature.
And the relationship to the laser diode here was that they’re having a different wavelenght by nature, as well.
Not seldomly, it’s an infrared diode that stimulates a crystal – which then radiates in various colours, depending on type.
Except for the ordinary, red laser wavelenght (6xx nm; 633 nm is what HeNe laser tubes used to use, for example).
That’s were true laser diodes exist for, without a crystal.
Speaking under correction, though, have to double-check.
Something maybe lost in translation, but lest anybody be mislead here: White LEDs ABSOLUTELY DO NOT “use a white filter”. They are a blue LED with (usually) yellow and red phosphors on top, that absorb most of the blue light, and fluoresce in the longer wavelengths. The combination of the fluorescent light and the remaining blue looks white.
Higher quality ‘white’ LEDs can use more phosphors to fill in some of the spectral gaps and give a closer approximation of a blackbody. But in no case is there EVER a “white filter” present.
A frozen glass cannot add colors to the spectrum of a LED. There is no such thing as a “white filter”.
The problem with LEDs is that the actual LED is just blue, and the “filter” is not a filter but a phosphor that converts some of the blue photons into yellow photons, and the combination of blue and yellow looks white but lacks most of the different colors present in actual white light.
And the first tube lasers were also exciting a crystal – ruby for example – with ultraviolet light emitted from a gas discharge, pumping the crystal with energy until it would produce laser light at its particular frequency.
“lacks most of the different colors present in actual white light”
No, it doesn’t. What a white LED lacks is things verging on infrared or ultraviolet. The stuff within the visible spectrum is just sometimes less or more than it should be; low quality ones will be too green and too blue and often very low on the reds. But they don’t completely lack those colors, they’re just uneven and in the wrong amount. Much like how daylight incandescent light bulbs used to work by using an aggressive filter to make the light cooler, you could make a more complex filter to clean up the spectrum of a bad LED. You’d be better off just using a good LED, since things like photography have caused there to be LEDs available that look perfectly decent.
This is a delightful project. I loved the successes and missteps. When I was a kid I remember going to a laser light show at the local planetarium. I believe the solution they use there is to spin one mirror at very high speed, and turning the laser on and off as Bitluni does here at the end. I think a high-speed spinning mirror overcomes the issue with trying to manage the stepping at a very high rate.
Fwiw, 405nm light seems to do a pretty good job exciting actual CRT phosphors, and you can really see the difference between a long persistence phosphor and the ‘normal’ kind in a TV.
Cheap led bulb phosphors are readily available, I’m not sure exactly how fast their response is, but it’s much slower than the types used for individual LEDs and many I have seen are slower than CRT phosphors. They also come in a range of colors, making for a number of fun possibilities.
Making a moderate resolution rgb grid wouldn’t be too difficult either, or deliberate segments to allow for characters and line art while only writing limited vector instructions.
If you want to play more with this idea, take apart a laser printer and a spinning platter hard drive.
The former has a spinning mirror disk thing that can do horizontal scanning of the laser beam, and the latter has the voice coil head actuator which can be used with a mirror to scan vertically.
These should both be fast enough to create a raster display.
You would need to create a new holder capable of containing the voice coil assembly which may or may not work well as a 3d printed item – there be strong magnets here – as well as getting everything aligned and working out the timing.
You might be able to actually use the voice coil in situ, but I’m not sure if or how you could control it without at least hooking it up separately to a controller – unless hard drives have some form of direct control protocol.
The spinny mirror disk thing from the laser printer should be a simple matter of plugging it in – though it might also be speed adjustable so that may also require a controller.
I cringed at every moment though this video and yet very amused and amazed at it as well
Great job!
But if you want to take it to the next level go back to the voice coil idea and start taking apart modern (not Winchester style) hard drives … that’s what I based my display on back in the day, but it used a yag laser to burn data matrix
I would improve by adding cheap galvos that can be bought on marketplaces and are originally meant for party lasers. Some of these are pretty fast and accurate, maybe fast enough for a SD screen.
The point was to make it more or less from scratch. This doesn’t require specialized components aside from the printed case, making it accessible to more people, and more fun.
Hmm, it occurs to me the next step might be something along the lines of common zinc glow in the dark paint. (Zinc Sulfide, copper activated) It can be quenched by red or infrared light, so an infrared light that flashes right before you begin to draw the next frame could help with ghosting while still leaving things drawn as long as possible when there’s no new frame to display.
Ooh. Now I want to make a SSTV display like this, mimicking the olde P7 phosphor CRTs.
https://www.taswegian.com/NBTV/forum/viewtopic.php?f=8&t=1318&hilit=mechanical+slow+scan
If you play carelessly with the intensity, bye bye Alderaan.
Milimeter by milimeter.
If they had high-quality full color lasers and galvos back then, they probably would have never bothered with the whole vacuum thing. But it sure is a lot easier to quickly steer a charged particle
Thing is, they used vacuum tubes to figure out what electrons and atoms were, so one kinda follows the other – can’t get a laser diode before you build a cathode ray tube.
I think that laser tubes are nice. Their light does sparkle so nicely and they have power.
Laser diodes are primitive, I think. They cheat by stimulating a crystal. And they must pulse for any meaningful output.
It’s like with the “white” LEDs that are actually blue with a white filter.
Still, laser diodes are fine for laser pointers and optical drives.
Calling phosphors a filter is more than a bit wrong, and calling direct stimulation a “cheat” isn’t any better, but I agree laser tubes have a bit more “romance” to them.
Hi, I meant to say that LED bulbs use a white filter (frozen glass etc) to create the illusion of being a white light source. In reality, they’re more blueish by nature.
And the relationship to the laser diode here was that they’re having a different wavelenght by nature, as well.
Not seldomly, it’s an infrared diode that stimulates a crystal – which then radiates in various colours, depending on type.
Except for the ordinary, red laser wavelenght (6xx nm; 633 nm is what HeNe laser tubes used to use, for example).
That’s were true laser diodes exist for, without a crystal.
Speaking under correction, though, have to double-check.
Something maybe lost in translation, but lest anybody be mislead here: White LEDs ABSOLUTELY DO NOT “use a white filter”. They are a blue LED with (usually) yellow and red phosphors on top, that absorb most of the blue light, and fluoresce in the longer wavelengths. The combination of the fluorescent light and the remaining blue looks white.
Higher quality ‘white’ LEDs can use more phosphors to fill in some of the spectral gaps and give a closer approximation of a blackbody. But in no case is there EVER a “white filter” present.
A frozen glass cannot add colors to the spectrum of a LED. There is no such thing as a “white filter”.
The problem with LEDs is that the actual LED is just blue, and the “filter” is not a filter but a phosphor that converts some of the blue photons into yellow photons, and the combination of blue and yellow looks white but lacks most of the different colors present in actual white light.
And the first tube lasers were also exciting a crystal – ruby for example – with ultraviolet light emitted from a gas discharge, pumping the crystal with energy until it would produce laser light at its particular frequency.
“lacks most of the different colors present in actual white light”
No, it doesn’t. What a white LED lacks is things verging on infrared or ultraviolet. The stuff within the visible spectrum is just sometimes less or more than it should be; low quality ones will be too green and too blue and often very low on the reds. But they don’t completely lack those colors, they’re just uneven and in the wrong amount. Much like how daylight incandescent light bulbs used to work by using an aggressive filter to make the light cooler, you could make a more complex filter to clean up the spectrum of a bad LED. You’d be better off just using a good LED, since things like photography have caused there to be LEDs available that look perfectly decent.
this is basically ldp, and this company manufactures them and i thinks has the patents https://www.prysmsystems.com/displays/lpd-6k-series/features/
This is a delightful project. I loved the successes and missteps. When I was a kid I remember going to a laser light show at the local planetarium. I believe the solution they use there is to spin one mirror at very high speed, and turning the laser on and off as Bitluni does here at the end. I think a high-speed spinning mirror overcomes the issue with trying to manage the stepping at a very high rate.
Fwiw, 405nm light seems to do a pretty good job exciting actual CRT phosphors, and you can really see the difference between a long persistence phosphor and the ‘normal’ kind in a TV.
Cheap led bulb phosphors are readily available, I’m not sure exactly how fast their response is, but it’s much slower than the types used for individual LEDs and many I have seen are slower than CRT phosphors. They also come in a range of colors, making for a number of fun possibilities.
Making a moderate resolution rgb grid wouldn’t be too difficult either, or deliberate segments to allow for characters and line art while only writing limited vector instructions.
If you want to play more with this idea, take apart a laser printer and a spinning platter hard drive.
The former has a spinning mirror disk thing that can do horizontal scanning of the laser beam, and the latter has the voice coil head actuator which can be used with a mirror to scan vertically.
These should both be fast enough to create a raster display.
You would need to create a new holder capable of containing the voice coil assembly which may or may not work well as a 3d printed item – there be strong magnets here – as well as getting everything aligned and working out the timing.
You might be able to actually use the voice coil in situ, but I’m not sure if or how you could control it without at least hooking it up separately to a controller – unless hard drives have some form of direct control protocol.
The spinny mirror disk thing from the laser printer should be a simple matter of plugging it in – though it might also be speed adjustable so that may also require a controller.
I cringed at every moment though this video and yet very amused and amazed at it as well
Great job!
But if you want to take it to the next level go back to the voice coil idea and start taking apart modern (not Winchester style) hard drives … that’s what I based my display on back in the day, but it used a yag laser to burn data matrix
Poorly lol
This is pretty hilarious use of a yag, even ages ago I just used a cheap pointer. Keep your goggles on !
I would improve by adding cheap galvos that can be bought on marketplaces and are originally meant for party lasers. Some of these are pretty fast and accurate, maybe fast enough for a SD screen.
The point was to make it more or less from scratch. This doesn’t require specialized components aside from the printed case, making it accessible to more people, and more fun.
Hmm, it occurs to me the next step might be something along the lines of common zinc glow in the dark paint. (Zinc Sulfide, copper activated) It can be quenched by red or infrared light, so an infrared light that flashes right before you begin to draw the next frame could help with ghosting while still leaving things drawn as long as possible when there’s no new frame to display.