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Thread: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

  1. #1
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    Default Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    OK so most of you here are so far above me when it comes to hardware mods that this thread will probably come off as laughably simple. But I wrote it up for another site and figured I'd post it here to just in case someone found it interesting, informative, or just wanted to laugh at my documented screw-up ;)

    ----

    A month or two ago I ordered one of these cheap lasers from Meritline for only $33:

    http://www.meritline.com/mini-laser-...--p-60905.aspx

    If you search around you can find videos of what they look like when they operate. Basically the effect is sort of a "shooting starfield" of red and green dots. You have some control of the speed of the effect, etc and can set it to blink to music it 'hears' over a microphone.

    Because I can never leave well enough alone, I thought it would be fun to try to modify it so that I could use an controller channel to control whether the starfield was "shooting" or "still". Essentially that involved toggling the power on an internal motor to the unit. This thread will document how to do the mod.

    Executive Summary:
    The basis of the modification was proved successful. As designed, the unit will operate as "factory" if the cord (which we will create below) is not connected, but connecting it allows motor selectability via a relay or other switch.

    However, I destroyed my laser in the process of doing the mod. This was because of an error in my technique and not because of bad mod design. So, I'm documenting this, including my fatal error, for posterity. If I replace this unit I will likely redo the mod on the new unit, avoiding my issues as I will describe later.
    Last edited by tfischer; 03-23-2012 at 10:22 PM.

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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    D I S C L A I M E R

    It's too bad I have to start out with this, but I feel I better cover my "assets" lol. This write-up is intended for entertainment purposes only. If you choose to do this mod, you are on your own. I'm not liable for any consequences of your decision to read this and/or follow any or all of the steps involved.


    S A F E T Y

    Lasers can blind you! Do not, under any circumstances, operate the laser with the cover off. Do not look into the laser while it's operating. Basically, don't be stupid. It's not worth your eyesight.

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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    Here's the supplies we'll be using:

    - The Meritline laser to modify
    - Some hook-up wire: 5' or so should do nicely
    - Heat-shrink tubing. You could substitute electrical tape but I don't find that to be as permanent.
    - 1/8" Mono phone jack. I used Rat Shack #274-0248 which just happened to be left over from a prior project.
    - 1/8" Mono phone plug. I used Rat Shack #274-0287 (also left over).

    Tools needed:
    - Soldering Iron
    - Drill and bit sized to your phone jack
    - Wire cutters/strippers
    - Philips screwdriver
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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    The first step is to remove the cover from the laser. Remember - NEVER operate the laser with the cover off!

    To do this we need to remove 4 screws, as hilighted in the two pictures below (I missed the arrow on one of them - you want the 4 topmost screws on the front and back).
    Attached Images Attached Images

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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    Now that the unit is open, we can explore where the jack can go. Note that there is plenty of room in the circled location. That's where we'll install the new motor jack - right next to the power jack:
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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    But before we do that - lets make the cable which will (eventually) plug into this jack. It will have the 1/8" mono plug on one end, and bare wires on the other end. We'll discuss later how this will hook up to the light controller.

    To make this cable, take a length of your hook-up wire - I used approx 4'. Double this back on itself, and chuck it into your hand drill. While holding the other end tight, start spinning the drill until it's nicely twisted. Once you're done, un-chuck the wire and cut off the loop.

    The pic below shows what you're going for:
    Attached Images Attached Images
    Last edited by tfischer; 03-23-2012 at 10:22 PM.

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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    Now pull out your soldering iron and solder on the 1/8" plug. It doesn't matter which wire goes where. Make sure the connections are nice, then crimp the strain relief:
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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    The next step is to prepare the jack.

    What we want to happen is as follows:
    - When nothing is plugged into the jack, the laser operates as if we had never done this mod at all.
    - When you plug in the cable we just made above, and the two bare wires are kept separated, the motor will stop
    - With the cable plugged in, and the two bare wires are touched together, the motor will spin.

    To accomplish this, we'll take advantage of a 'feature' built into these jacks: a switch that opens when something is plugged in. If you use the RS part # I mention above you can do the mod exactly as I did here. If you use another jack, you'll have to do some exploring to make sure you get the pins correct. Here's what I found, with some experimentation:

    With the jack oriented as in the picture below:
    - When nothing is plugged into the jack, the left and bottom pins are shorted together.
    - When the jack gets plugged in, the left and bottom pins are no longer connected.
    - The leftmost pin corresponds to one wire of the plug, and the rightmost the other wire (for our application, it doesn't matter which is which).

    If you think about it, this means that you can short the bottom and right pins together, and then connect this as a switch on the motor power wire (with the motor going to the left and bottommost (or rightmost, since they're shorted) pins to get the behavior we want:
    - When nothing is plugged in, the jack shorts the left to the bottom, and we shorted the bottom to the right, so power flows right through the wire as if nothing is there.
    - When our jack/wire is plugged in, the connection is broken. Instead, power flows through one wire, and returns through the other. If the wires are connected, e.g. with a relay or switch, the motor will spin.

    If you didn't understand any of that, just buy the RS part # I used and wire it up this way:
    - Take a very short wire and solder it to the rightmost pin.
    - Take a longer (e.g. 6") wire and solder it to the leftmost pin.
    - Take another 6" wire, twist it onto the other end of the short wire from the first step, and then solder it to the bottom pin.

    Basically make it look like the picture below:
    Attached Images Attached Images

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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    Next we will drill the hole for the motor jack. It will go right next to the power jack, as shown in the picture below.

    BE VERY CAREFUL WITH THIS STEP! THIS IS WHERE I DESTROYED MY LASER. When you drill metal, the bit will break through very quickly, and if you're applying any pressure at all it will shoot right into the unit. My bit slammed right into the tiny circuit board that drives the green laser. Although I tried to revive it, I was unable to. The motor and red laser still work so I was able to verify this modification works as designed, but unfortunately I killed the green due to my carelessness.

    If I do this again, I would do the drilling on my drill press, where I can control depth much more accurately. If you need to use a hand drill, be VERY CAREFUL.

    Also once you drill, make darned sure all metal residue is shaken/vacuumed/whatever out of the unit - you don't want it shorting something out.
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    Default Re: Modifying a "Cheap Chinese" Red-Green starfield laser to allow for motor control

    I didn't even realize I did any damage at this point so I carried on.

    1) Thread the jack through the hole, and tighten it securely.
    2) Unplug the little jack which powers the motor. This is the one circled, and can be easily identified because it's the only one with small-gauge wires going to it. Untangle it from the mess so you have some wire to work with.
    3) Cut the red wire going to the molex plug, a few inches from the plug.
    4) Use the heat-shrink and solder one end of this newly cut wire to one of the wires going to your jack. Solder the other wire to the other wire going to the jack. You can cut your "jack wires" to an ideal length and twist them to keep them neat.

    The second picture below shows my result. As an aside if you compare it to the picture earlier in this thread, you'll see how badly I toasted the little circuit board going to the green laser (the large heat-sink in the middle of the unit). I didn't even notice it at this point.
    Attached Images Attached Images

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