BB target (general impact sensor)

Discussion in 'The Projects Forum' started by awdark, Jul 20, 2012.

  1. awdark

    Thread Starter New Member

    Oct 29, 2009
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    Wow the similar thread feature is very nice. But not quite what I seek.

    I have a simple idea that is getting over complex in my head and I wanted to get some ideas.

    I want to make 3" diameter targets for BBs that will light up upon impact. Simple version will stay on, next hit turns off. Complex version will blink then shut off.

    I want to have multiple modules attached to a surface so that I will know which one I hit.

    I would consider switches similar (or from) a mouse, short throw and fairly little force needed to activate this. Piezo mic attached to a sheet of wood might work well too, but I don't know if it will just activate all in an area.

    Since I don't know if it will work, I have a few of the MSP430 kits on hand, 555 timers, and other miscelaneous parts. What is the easiest most simple way to do this.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U want a blinking target?
     
  3. wayneh

    Expert

    Sep 9, 2010
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    You'll want those timers - that'll be an easy way to control the response of the lights. For instance, you could have it stay on 3 seconds following a strike.

    The challenge is how to generate a trigger. A piezo element would do it but I'm at a blank how you can get a 3" diameter AND a surface that can stand up to repeated bb strikes. A regular mic behind a metal plate would "hear" an impact anywhere on the plate. Maybe you could just glue little cellphone-type mics to the backs of metal plates. You'll likely need to amplify the result to a signal large enough to trigger the timer.
     
  4. awdark

    Thread Starter New Member

    Oct 29, 2009
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    BBs don't carry too much energy, I'm actually unsure if it has enough to move a mouse button. A sheet of 1/4" plywood should be more than enough to stop it. I'm not sure if there will be a concern about the duration of the "on" state.

    @R!f@@ - I would want it to only turn on after it detects something so I can have a visual confirmation.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    What U need is a couple of strain gauges

    Glue them at the back of the target and test it first.

    It's not gonna be easy to do this u know.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Well, the impact is an awfully brief event - you might miss the flash of an LED. But a quick flash can be done without a timer circuit, so that might simplify things a bit. You could use a quad comparator to watch 4 targets at once, with an RC tank on the outputs to slow it down just a bit for better visualization of an impact.

    I still like the idea of using vibration/audio to detect an impact, but maybe there's something even cheaper. I think you'll struggle with anything with moving parts, like a switch. There are tiny pushbutton switches, and if your target was 1" instead of 3", I could imagine maybe using one of those. But a bb doesn't have enough inertia to move much more than the pushbutton itself.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Have you ever been shot with a BB? I have. It went under my skin. I tried just now to push a mouse button under my skin but was unsuccessful. Therefore I posit that a BB has ample energy to actuate a mouse button. Actually, I suspect a BB has enough energy to shatter a mouse button, and probably the PCB beneath it too.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    There's a difference between inertia (needed to move a target) and energy (breaks stuff) delivered to a target.

    But anyway, the OP may enjoy this example of how our tax dollars were used to develop something very similar.
     
  9. strantor

    AAC Fanatic!

    Oct 3, 2010
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    How about making you plate hang from a pivot at the top. at the bottom it could rest against a piece of metal. when you shoot it, it swings out a bit, breaking contact with the metal, and registering as a hit.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Definitely could work. Good one. :)
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Last edited: Jul 20, 2012
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Actually, it could be pretty simple to just flash the target; if you used a crystal as a piezo sensor. When struck, the crystal will generate a voltage that will be rectified and used to turn on a MOSFET, which will allow current to pass through LEDs.

    Here is a thread that has a circuit you could use; it's pretty simple and cheap.
    http://forum.allaboutcircuits.com/showthread.php?t=32636
     
  13. BillB3857

    Senior Member

    Feb 28, 2009
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    For a multi-zone circular target, concentric open center metal disks of various sizes with gaps between for isolation mounted to a foam back board. Each disk would have its own piezo sensing a hit anywhere on the disk.
     
  14. Sensacell

    Well-Known Member

    Jun 19, 2012
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    This sounds like a fun project!

    One approach:

    Take some disks of Lexan polycarbonate plastic, maybe 1/2" thick.
    (clear and super tough plastic) stick the guts of one of those large piezo beepers on the back side with double face tape.

    Inside a beeper you will find a round brass disk with a large ceramic element bonded to it, these things can detect vibrations really well. In a beeper, the input signal is converted into mechanical vibrations, (sound) you will just be using it in reverse. The output signal will be a surprisingly large AC voltage that you can send to a comparator to set a detection threshold.

    You will need to mechanically isolate the target disks from each other, so the vibrations do not cross-couple to the other targets, maybe mount them on some foam?

    You can then put LED's behind the disks to light them up.

    Beware of rebounding BB's! they love eyeballs!

    (you guys are too fast- already way ahead of me)
     
  15. BSomer

    Member

    Dec 28, 2011
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  16. Markd77

    Senior Member

    Sep 7, 2009
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    If you wanted a more complicated project using the microcontroller, you could use 3 or 4 sensors attached to corners of a sheet of wood. By measuring the timing differences you should be able to tell where the pellet hit.
     
  17. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You'll put your eye out, kid.


    :)
     
    strantor likes this.
  18. awdark

    Thread Starter New Member

    Oct 29, 2009
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    I will take a look at the links.
    I was thinking multiple smaller targets would be easier to isolate than a large one with zone detection hence my original strange sounding idea with small 3" discs

    The circuit with the MOSFET and piezos sound quite interesting.
     
  19. awdark

    Thread Starter New Member

    Oct 29, 2009
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    I don't see an edit button but to update, in the end I got lazy and just assembled a 555 in monostable mode. I still want to try the other idea to use a piezo element and the completely excessive idea about triangulation is even more amusing. But for now that's what I did and I wanted to thank you guys for the ideas.

    I will need to re-enforce the thing, maybe actually use a smaller target as originally intended but http://www.youtube.com/watch?v=ejzfkTkk91g&feature=youtu.be

    For now it is a CD with 3 mouse buttons, I added some foam to fill the gap and taped 5 CDs together to form a front. That front was taped to the rear CD with the buttons and so far it works but was shows quite a bit of damage and is pretty much destroyed after that short session with the two weak BB guns (one bb pistol and one red ryder which are both inaccurate and weak compared to the pump type)
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    I think a little piezoelectric sensor or microphone should do it.
     
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