Display Possibility

As a Peachy supporter, but also an xmas light dabbler, I have been looking at programmable laser light show projectors for some time. I have been dithering for some time, as reviews and durability of some offerings have been less than favourable. These projectors, in principle, are basically the same guts as the peachy. I was therefore happy to find a device which could 3D print AND potentially fill the role of programmable laser display. Although to realise its potential, could require considerable software effort.

Aren't you concerned about the laser hitting someone's eye? Maybe that is a bigger problem for Halloween. (Happy Halloween everyone)

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Originally Posted by Anuvin

Aren't you concerned about the laser hitting someone's eye? Maybe that is a bigger problem for Halloween. (Happy Halloween everyone)

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Might need to switch the 20mw laser for a 5mw for this purpose..... I thought I read somewhere that the laser could be switched. A 5mw laser is pretty safe.... and the laser beam is moving.. so wud not remain concentrated on one spot for long.

The Peachy Printer's laser system works on a similar principal as do laser light shows, but the requirements are quite different. Laser light show projectors need to move fast enough to provide persistence of vision, but we don't need to move nearly as fast while curing resin. They tend to also cost a lot because of the precision parts involved. Overall, I don't think the Peachy Printer unit (at least the base model) will be usable as a laser light show -- it will be too slow. That said, it's meant to be hackable, so modifying the parts or replacing them with others may get you what you need. If you are interested, try it out -- we'd love to see what you come up with.

Errrr, I wasn't really after a high refresh rate..... initially just text messages projected onto the house..... these don't even have to scroll.

It still has to move very fast. The problem is that the laser projects a dot. If you want to see an image or test, you have to move that dot across the surface so fast that the human eye doesn't realise that it's actually just a moving dot.

Think about how a CRT monitor works, with the electron beam scanning across the rows. On a 60Hz 640x480 screen that requires a scan line rate of 28.8kHz (ie scanning 28800 lines per second). This is a bit easier than the Peachy's job because the phosphor in the screen has some persistence (it stays lit up for a while after the beam hits it) so you do only need to scan at 60Hz. Without that phosphor (which the Peachy obviously won't have) you're relying on the human eye's own persistence. It appears that to use this well you need to run at 100Hz or so.

Now you have to find out how many lines are needed. Say the Peachy projects a dot 5mm across (when the target is a wall a few metres away). If you want a display 2m high then that'll be 400 lines. 100Hz and 400 lines is a 40kHz scan rate - you have to be flicking the beam back and forward 40,000 times per second. So, even for static text, the beam needs to be moving seriously fast.

My understanding is that the proper laser projectors manage this by having the beam oscillating back and forward for the scan lines, which allows for very high speed without needing complete actuation. They probably also use much larger dots to cut down the number of lines.

The Peachy isn't built for this sort of use. It's designed to move slowly (relatively) but with a lot of control over position and velocity. It's almost certainly designed not to oscillate, because oscillation makes control much harder.

It doesn't work on a raster basis, it works on a coordinate system. There is no "fly-back" each move is on a calculus type basis i.e. delta X and delta Y. Observing the sample printing video, the speed looks more than adequate to display stationary text. The beam is divergent, so there is no extra requirement for a large display, other than to move it further away from the 'screen'. It would be nice to show "Merry Xmas 2013 from Mike" writ large across my house. If the CAD package blender can render text as a 3D object, it should work quite well.

The Peachy doesn't use rastering, but I'm pretty sure the laser projectors do. That's the problem - a Peachy trying to act like a laser projector is working in a mode it was never meant to do.

I suppose that if you just did the text as a single-line vector then it might be quick enough, although I wouldn't count on it (you still need to scan the text very quickly in order to make it appear steady to a human eye). The problem with this is that a single line vector will be about a millimetre wide, and text a metre high with lines 1mm wide is going to be very difficult to read. To make it usable you need to rescan over the text hundreds of times with a slight offset, so it appears thicker - but that means more lines and a lower refresh rate.

In addition to the slew rate of the mirrors, to do a raster-type display you would also need fine control to turn the laser on and off. Our laser on/off is too coarse to accomplish that. That said, the laser light shows I have seen were definitely vector, not raster. Maybe we're talking about two different things, though.