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Thread: 15kpps scanner signal, what are the values?

  1. #11
    Join Date
    Mar 2012
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    I offer a very nice kit called The LaserBoy Correction Amp for exactly this type of application.

    http://laserboy.org/forum/index.php?topic=561.0

    $40 plus shipping.

    This kit is designed for audio DACs that output all positive voltage. It works very similar to the schematic that was posted above but instead of a fixed +5VDC regulator, it uses a variable negative voltage regulator that goes into the non-inverting input of the op-amp. The driving signal goes into the inverting input, so your control signal ends up inverted. No big deal. You just invert your control signal in software. The nice thing about this kit is that is it very easy to tune it for just about any kind of computer controlled DAC that operates in the all positive voltage domain. The kit comes with all the parts including the DB25 ILDA port and a DC/DC converter that operated on +5VDC and provides +9V and -9V for the TLO82 op-amps, so you can drive the board with USB supply voltage. All of the precision resisters were measured and matched to 3 digits on the meter. The board is populated for 6 channels so you can use it to drive scanners and 4 channels of color modulation. The color mod channels have 5V zener diodes on them to prevent anything over 5V from getting to your color mod inputs.

    PM me if you are interested.

    James.
    Creator of LaserBoy!
    LaserBoy is free and runs in Windows, MacOS and Linux (including Raspberry Pi!).
    Download LaserBoy!
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    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.

  2. #12
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    May 2018
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    Quote Originally Posted by aberry View Post
    Does the +5V have to come from a +-5V psu or will an ordinary 5V psu work? just noticed the -5V pin from the psu is not used. Also any chance a more common ic than OPA1654 could be used? Thank you.

  3. #13
    Join Date
    Aug 2013
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    The op amp in the schematic was grabbed at random from my library, but it will work nicely with a supply of only +/-6V or so. If you're using a supply of +/-9V or higher, then you can easily use a TL07x or TL08x op amp, which are super common--or just about any other common audio op amp, really.

    An ordinary 5V supply will work fine for the reference voltage, but the op amp needs a +/- supply. You can use the +/-12V supply from your galvo drivers to power the op amp, and then use a simple 7805 regulator to provide a 5V supply from the +12V for the reference.

  4. #14
    Join Date
    May 2018
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    Thank you again!
    I got all the parts and ready to solder. Should I connect the middle pin of the 7805 regulator to the GND of the +12V of the +-12V PSU or should it be done differently? First time working with +- PSUs.

  5. #15
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    Yes.

    The PSU should have three output terminals. One +, one -, and ground. The middle pin of the voltage regulator goes to ground on the psu.

    Adam

  6. #16
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    May 2018
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    okay

    now for more hardware related question.

    the specification mentions max scanning angle of 45-50 degrees. Firstly I am not sure why its not an exact number. And second question, is it possible to be increases in cost of even slower scan speeds?
    Attached Thumbnails Attached Thumbnails Capture.PNG  


  7. #17
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    Aug 2013
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    There are a couple of different limiting factors on scanner speed depending on your use case. The first is performance, and light show scanners are usually specified for maximum performance at an angle of 8°. If your scanners are rated, say 30k@8°, then anything larger than that will result in diminished performance. Attempting to go too wide without reducing the scan rate or otherwise adjusting your content can result in damage to the scanners, but usually you'll see the image quality start to degrade well before that happens. The second limit is what the scanners are mechanically and optically capable of. The motors themselves will have a maximum mechanical range, and you'll need to keep below that with enough headroom that any overshoot will not cause the motors to slam into their hard mechanical stops--or cause the mirrors to smack into each other. Optically, the shapes of the mirrors will also limit the scan angle for a given beam size. At a certain point, the mirrors will be at too much of an angle to capture the entire beam, and you'll see the brightness drop off or the color balance shift at the extreme edges of the scan field.

  8. #18
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    May 2018
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    I understand all the limitations besides the mechanical one. Are there literal physical barriers that prevent shaft rotation angle? If yes, has anyone attempted to modify a scanner and make it open loop or increase the rotation range?

  9. #19
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    Normally no. Some scanners will scan at 90° but it isn't practical to scan that large since the exiting beam would hit mirrors/scanner block... things like that. So, the limitations come back to the physics of the scanners. Most scanner manufacturers limit the rotational range based on the type of sensor feedback used in the scanner. If they were to scan larger, the feedback sensor would cease to work past a certain angle e.g. single emitter with a flat blocking "flag". Past a certain angle renders the feedback sensor/s useless.
    Last edited by absolom7691; 05-30-2018 at 10:21.

  10. #20
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    May 2018
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    I see.

    I noticed an issue I have with the schematic drawing after building a proto board.

    Click image for larger version. 

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    I don't see what I need to connect to the negative pin (or positive?) of the output +-5V connector that goes to the scanner.

    There's only one rail going to the "+-5V out"

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