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Thread: Using laser galvo projection for live vector graphics from Raspberry Pi

  1. #1
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    Laser Warning Using laser galvo projection for live vector graphics from Raspberry Pi

    Hello everyone,

    I'm new here so I hope this is the right place for this thread.

    My plan is to make a collimated light projector for use as a HUD. All the graphics will be drawn by a raspberry pi with data from outside sensors.
    I was considering using a simple small LED projector and collimating that, but they are pretty bad in terms of efficiency, and output a ton of heat for not that much light, and pretty bad blacks.

    All I need is green lines anyway, so 2/3 of that projector goes to waste, and Vector drawing seems way cooler.

    I've been looking at galvo sets like this or this on ebay. These seem like a right choice in terms of cost.

    My question is, how can I output Vectors live from the Pi to those galvos. the boards that come with it have microphones, so I think this is for a musical show type thing, so It might by difficult.

    Again, quite the novice at this whole laser thing, so any info/idea is greatly appreciated.

    Thanks.

  2. #2
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    ... when experimenting with the cheap galvoscanners I've built a setup around the "EasyLase LC USB" DAC - https://www.mylaserpage.de/DACs.html

    Then ist's mostly sending some data-arrays to the USB-port of the DAC and it will set the analogue voltage to the servos.

    Check for other openSource Galvoscanner/DAC-projects - there are several around ...

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  3. #3
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    You could build your own laser DAC using a USB sound device. The USB SND8 (generic name) uses the CM-6206 chip. It is 8 channels of 16 bit 48KHz for less than $20. You need a correction amp to make it compatible to an ILDA control port on a laser projector.

    Although it is not real-time and you can't stream live from it, LaserBoy compiles and runs very well on a Pi. It reads and writes ILDA, DXF, ASCII text and wave (all as vector art) and bitmap files as raster.

    If nothing else, you would have something fun to play with and you will learn a lot about how all of this works.

    All you need is a wave player like aplay in the command prompt or whatever in the GUI to play the LaserBoy waves to your DAC.

    http://laserboy.org/forum/index.php?topic=561.0
    Creator of LaserBoy!
    LaserBoy is free and runs in Windows, MacOS and Linux (including Raspberry Pi!).
    Download LaserBoy!
    YouTube Tutorials
    Ask me about my LaserBoy Correction Amp Kit for sale!
    All software has a learning curve usually proportional to its capabilities and unique features. Pointing with a mouse is in no way easier than tapping a key.

  4. #4
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    or just buy this

    https://www.tiltfive.com/

  5. #5
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    Quote Originally Posted by Lascar12F View Post
    Hello everyone,

    I'm new here so I hope this is the right place for this thread.

    My plan is to make a collimated light projector for use as a HUD. All the graphics will be drawn by a raspberry pi with data from outside sensors.
    I was considering using a simple small LED projector and collimating that, but they are pretty bad in terms of efficiency, and output a ton of heat for not that much light, and pretty bad blacks.

    All I need is green lines anyway, so 2/3 of that projector goes to waste, and Vector drawing seems way cooler.

    I've been looking at galvo sets like this or this on ebay. These seem like a right choice in terms of cost.

    My question is, how can I output Vectors live from the Pi to those galvos. the boards that come with it have microphones, so I think this is for a musical show type thing, so It might by difficult.

    Again, quite the novice at this whole laser thing, so any info/idea is greatly appreciated.

    Thanks.
    You will find lots of opinions here based on our experiences and preferences.

    I found this on Google: http://www.jeffhove.com/robots/LaserProjector.html
    It is a project that uses a raspberry PI and a SPI DAC. I had been looking up how to use the DMA capability of the PI to write to SPI or at least IO ports so I could send to one of my OLSD boards: http://www.fab-favreau.com/index.php...enLaserShowDAC

    I had wanted to take advantage of IDN (ILDA Digital Network) using a RPi. My project uses an Arduino to talk to a DAC board over SPI and a few IOs for selecting which chips to talk to. It handles the analog voltage stuff for you.

    I think you could put something together for fairly cheap. A green laser diode (just go for TTL on/off control for now) and a set of scanners. Since your HUD might have a small FOV / projection angle you might be able to get away with just 0-5V output from the DAC. I would recommend at least buffering this with an opamp voltage follower.

    Let us know if you have any questions.

  6. #6
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    Ha ha. I think we forgot to answer the basic question.

    How do you output vectors to a set of Galvos?

    The galvanometers take an analog input signal and translate that to an position. The inputs are differential meaning they have a + and a - signal input (+5V to -5V) that mirror eachother. You can also connect it up as single ended meaning there is just a ground and a + signal input (-10V to +10V). The most convenient way to command it from a digital device is to use a DAC (Digital to Analog Converter). This could be a set of resistors (R2R DAC resistor ladder), a IC circuit, or a semi/intelligent device that you just send point data to and it does all the work. Here is a schematic diagram of my older (more simple) OLSD (Open Laser Show DAC) board. It has a decent example of a DAC chip and the necessary circuit to change its output from 0-5V to +-5V differential. It also has 3 resistor ladder DACs (2 and 3 bits) to control the level of the color. These are simple and if you want to use something like that for X and Y position you will want at least 8 bits. If you do any more bits than that get a DAC IC, they are easy to interface and are relatively inexpensive.

    Click image for larger version. 

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    This instructable also has a much better explanation of how it works and a simple circuit to interface to an Arduino which could easily be a Raspberry PI. https://www.instructables.com/Arduin...h-Real-Galvos/

  7. #7
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    Thanks for all the helpful and quick replies guys

    To be sure I understand this right, in those links I put in my message, the galvos are connected to driver boards. I have to feed those boards an analog signal ? or are you guys talking about driving the galvos directly, and not using the boards that come with the "kit" ?

    If so, from the kind of gear you recommended, I assume a commercial audio grade USB DAC wouldn't have the performance needed to get nice sharp angles and lines ?

    Do I have to go through ILDA ? It seems limiting from the point of view of what i'm trying to do, which is pushing RaspberryPI live generated ~100 line SVG at 30Hz (hopefully). ILDA seems geared towards text and pre-generated SVG gifs, is that correct ?

    Would driving the boards from a consumer audio USB DAC via coax be possible ? or would the accuracy be way to bad to get readable info ? I need to be able to read numbers clearly.

    Sorry for the ton of questions btw, y'all are great help so far
    Last edited by Lascar12F; 10-12-2020 at 17:59.

  8. #8
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    The boards that come with the galvos are special galvo amps that both drive the galvos and sense their position. ILDA is really 2 things. It's a pinout standard for analog signals that drive a projector, x y r g b and so forth. It's also a file format for color vector art for laser projectors. A laser projector works much like an oscilloscope. Two signals are required to move the beam x and y. A modified sound device can produce just as good of a display as any other kind of laser projection controller.
    Creator of LaserBoy!
    LaserBoy is free and runs in Windows, MacOS and Linux (including Raspberry Pi!).
    Download LaserBoy!
    YouTube Tutorials
    Ask me about my LaserBoy Correction Amp Kit for sale!
    All software has a learning curve usually proportional to its capabilities and unique features. Pointing with a mouse is in no way easier than tapping a key.

  9. #9
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    Oh I think I understand your fist message now James.

    So a decent quality audio DAC would work fine, but I need to get those values within what ILDA will understand so I need a modified amp is that correct ?

    I think is greatly simplifies my problem. I just need to make a program that takes the SVG matrix I output and reads it in voltages one by one over audio, shouldn't be too hard.

  10. #10
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    Or you could convert your svg data to dxf and open that in LaserBoy. There is actually quite a bit involved in time optimization of art. This is the process of adding points along lines and in corners to control the scanners' velocity and make the image look as good as possible. That's what LB does.
    Creator of LaserBoy!
    LaserBoy is free and runs in Windows, MacOS and Linux (including Raspberry Pi!).
    Download LaserBoy!
    YouTube Tutorials
    Ask me about my LaserBoy Correction Amp Kit for sale!
    All software has a learning curve usually proportional to its capabilities and unique features. Pointing with a mouse is in no way easier than tapping a key.

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