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Thread: Frameless Laser Harp with microcontroller

  1. 2nd Place Frameless Laser Harp with microcontroller

    LASER HARP - Driven by Arduino
    Stephen Hobley - February 2008

    INTRODUCTION:

    When I was 15, I saw Jean-Michel Jarre play the laser harp during the Rendezvous Houston concert. I thought it was the coolest thing I'd ever seen. I knew one day I would build my own, and it would open, close and work without a frame, just like his.

    Essentially it's a 'virtual' playing surface. Each beam is one note, breaking a beam sounds the note, and releasing it silences it. You can modulate the sound by moving your hand along the beam (although this still needs some final tweaking)

    It's only taken about 22 years, but I finally got the bugs out of the sensor last week.


    ...and a couple of pictures...






    PROBLEMS:
    • The first problem was that we needed something to produce a +/- 10v p-to-p staircase waveform to drive the galvanometer mirror at approximately 600Hz.
    • The second problem was to create a detector that would reject both ambient light and anything outside of the 532nm frequency of the laser light. The detector would have to operate over a long range (6ft +) and be stable enough to operate under stage lighting.
    • Finally a serial port (MIDI) output routine was required to sound the notes.
    SOLUTIONS:

    LASER CONTROL:

    Basically an Arduino connects to a 12-bit DAC chip (TLV5618) using the SPI 3 wire interface. It sends numbers on a timer interrupt to the DAC to specify where the beams are, 0, 455, 900, etc... all the way up to 4095 for 10 beams.

    It holds each position for about 500uS (half a millisecond) and switches laser blanking on (or is that "off"?) for this time.

    When it reaches the end it brings the mirror back to the start position.
    The output of the DAC chip is 0-5V - this is then converted to -5v / +5v using a TL082 Opamp chip from Radio shack.

    Finally it's passed through a Balanced Line Driver chip to give the full (-/+ 10v ptp) differential signal required by the mirror (laser galvanometer) amplifier.

    REFLECTION SENSOR:

    The reflection sensor is wired into pin 2 of the Arduino, on it's hardware interrupt line - so when this is triggered the Arduino stops processing for a uS or two to record the beam pulse in an array. This routine has to be very short. I noticed some double pulses on the output from the beam sensor, so I added a 555 timer in astable (monostable?) mode. This is triggered by the first falling edge of the sensor and outputs a solid single pulse.

    It uses TAOS (#12) light to voltage sensors, that are wired into a two opamp differentiator circuit that rejects ambient light (so the circuit only sees flashing laser pulses, anything that is on all the time is rejected). The opamps are tuned to the approx frequency of the flashing laser light. This was the hardest part of the project, and for a long time I did not think I could get it to work (and that maybe JMJ's harp was a fake).

    Then by accident I wired one Opamp to +5v not ground, and forgot to wire the other one to ground, and as if by magic the sensor started to "see" the pulses being reflected off the far wall of the dining room.

    The standI built a small stand for the sensor and have this attached to the harp via a 6' cable. The harp also has footswitch control. In this way the harp can be below the stage (like Jarre) and the sensor and control next to the player. You can get larger beam spread this way, as the laser mirror is limited to 40 degree range.

    Here's a picture - 3 TAOS cells, with 532 notch filters - the pot on the stand is to adjust the sensitivity (although it seems to range from incredibly sensitive, to insanely sensitive). The 450mw laser is too bright for the sensor, the smoke sometimes sets notes off. Originally it had a 250mw laser - which works very well, but not so visible.


    It went through many revisions - I tried a whole bunch of cds cells and photodiodes, but ended up using the Texas Instruments TAOS light to voltage convertors. There are a couple of tricks being used to increase sensitivity, so that ambient light is rejected.

    MIDI:

    Finally a MIDI output routine is running on the main thread of execution and processes any MIDI messages to be sent out of the TX pin of the Arduino. Optionally the amount of reflected light is also read by one of the ADC pins and this is scaled and transmitted as MIDI continuous controller data. It can be mapped to any controller number. So sliding your hand down the beam can 'bend' notes, or sweep the filter etc... This is not 100% reliable (or musical ) so I tend to turn that off.

    There's also an LCD status panel on the top that is also serviced by this thread.

    OPERATING PRINCIPLE:

    This diagram, from my friend Manuel Schultz's Laser Harp site shows how it works - the only difference is that I have the sensor in front of the player, rather than below.


    PUTTING IT ALL TOGETHER:


    BLUE SECTION - Laser and PSU, 450mw 532nm laser with TTL blanking
    RED SECTION - Galvanometer, Amplifier and PSU
    GREEN SECTION - Arduino, DAC, Line Driver and Return sensor

    It used to have 2 lasers - one red, one green as I wanted the beams to change color when played, but I couldn't find a red laser to match the 450mw green. Mine was only 250mw.



    PARTS:

    Laser - Ebay (magicmerlin)
    Galvanometer - Ebay (lasershowparts)
    Arduino - available from Trossen Robotics
    TAOS Sensors (#12) - www.mouser.com
    TLV5618 DAC, SSM2412 Line driver both from www.digikey.com

    More info: www.stephenhobley.com/build

    UPDATE:

    I just discovered tonight that if you remove the IR filter on a WiiMote and replace it with a 532nm notch filter the hardware blob tracking can be used to track my hand positions while playing the harp. (I finally got my tri-wing screwdriver in the mail)

    This is so cool, and it solves all the non-linearity issues I was having using reflected light level - so I'll be updating the harp to use the WiiMote tracking ASAP.

    It's probably not fast enough to completely replace the trigger sensor, but it'll work for pitch-bending etc...
    Last edited by shobley; 02-28-2008 at 03:47 PM.

  2. Re: Frameless Laser Harp with microcontroller

    Quote Originally Posted by shobley View Post
    When I was 15, I saw Jean-Michel Jarre play the laser harp during the Rendezvous Houston concert. I thought it was the coolest thing I'd ever seen. I knew one day I would build my own, and it would open, close and work without a frame, just like his.
    ...
    It uses an Atmel MPU to control the laser on a timer interrupt, beams bounce of your hands and are detected by a light sensor on the floor, that triggers MIDI output on a pin interrupt.
    Wow, Steve. That is awesome. I love weird musical interfaces, especially ones involving lasers. Now you gotta get yourself a pair of big reflective sunglasses like Jarre wears.

    So, is this one laser pulsing at a rotating mirror? What are you using for the light sensor?

    Quote Originally Posted by shobley View Post
    http://www.youtube.com/watch?v=sLVXmsbVwUs

    (anyone know how the 'YOUTUBE' button works? I can't seem to get it to work)
    http://forums.trossenrobotics.com/fa...faq_youtubetag

    Use the video ID. It's what comes after ?v= in the URL.

    Last edited by Dave; 02-12-2008 at 02:33 PM.
    New to the TR Community? Feel free to introduce yourself and show off your projects!

  3. Re: Frameless Laser Harp with microcontroller

    Hi,

    That's pretty cool ... and I want to build one too ...
    ... are you posting the basic plans and code soon?



  4. Re: Frameless Laser Harp with microcontroller

    Thanks!

    <snip>

    (Moved to top of thread...)

    Eventually I'll be posting the construction details on my website
    Last edited by shobley; 02-25-2008 at 08:53 PM.

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    Re: Frameless Laser Harp with microcontroller

    more cowbell! I mean more videos That is way freakin cool!!

    thanks for the submission Steve

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

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    Re: Frameless Laser Harp with microcontroller

    Wow, great project. I heard that those TAOS sensors were discontinued and that they were just going to sell out the remaining batch. I've always wanted Phidgets to make a board using those. I don't know how big the market would be for them, but they would be cool. You can make laser harps and M&M sorters!

  7. Re: Frameless Laser Harp with microcontroller

    Discontinued...?

    Nooooooooooooooooooooooooooooooo!!


    It took me *ages* to find something that worked.

    Actually I think some of them are discontinued but I used the '12' series. Hopefully they'll be around for some time yet.

    I just uploaded a slightly longer video - and actually managed to make it to the end of Rendezvous Part II without goofing up!



    It used to have 2 lasers - one red, one green as I wanted the beams to change color when played, but I couldn't find a red laser to match the 450mw green. Mine was only 250mw.

    Steve
    Last edited by shobley; 02-25-2008 at 08:54 PM.

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    Re: Frameless Laser Harp with microcontroller

    WOW!

    That is so damn cool Steve! Arduino huh? Man, I see those used everywhere lately! I need to start learning more about them.

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  9. Re: Frameless Laser Harp with microcontroller

    <snip>
    (Moved to top of thread...)
    Last edited by shobley; 02-25-2008 at 08:54 PM.

  10. Re: Frameless Laser Harp with microcontroller

    <snip>
    (Moved to top of thread...)
    Last edited by shobley; 02-25-2008 at 08:55 PM.

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