Snapping pics at the right moment with a pressure plate

[BiOzZ] built a pressure sensitive camera accessory to snap pictures at just the right moment. Before turning out all the lights the camera is set up with a twenty-second timer and a three-second exposure. The pressure plate doesn’t take the photo, but fires the flash to catch an image in the middle of the action.

The hack uses a piece of acrylic as the base of the pressure plate. A switch is constructed by placing aluminum tape on the base, and attaching a thin metal strip that is bent to add just a bit of spring. When an object is place on the plate the thin metal contacts the aluminum tape completing the circuit, a change in the weight breaks it. A simple circuit connects to this, using a relay to actuate the flash from a disposable camera. This is perfect for documenting the moment when you exercise that fruit-induced rage that has been consuming you lately.

Comments

  1. blodgar says:

    Photo inspired by the famous Allman Bros. album, “Beat a Peach”!

  2. Bob says:

    But if all the lights are out, how can you accurately swing the bar and hit the peach??!!

  3. Jake says:

    Haha, cool!

  4. Entropia says:

    I made a similar system a few years ago. I used ATmega16, a microphone and a single-use disposable camera with flash.

    Result:
    http://entropia.1g.fi/kuvat/Muut/Kuvailua/lightbulb+disintegrating.jpg
    http://entropia.1g.fi/kuvat/Muut/Kuvailua/waterballoon4_big.jpg

  5. This is awesome. My only problem is that working in the dark, I’m just as likely to hit my camera as I am the peach. If this could fire both flash and shutter, it would be even awesomer.

  6. pod says:

    @bob: was thinking the same thing

  7. nubie says:

    Can I strap this to the underbelly of a car and catch some sweet tire deformation? It could be triggered by a lateral acceleration sensor ;)

    Although drifting around at night is bound to be illegal and dangerous. So I needed a good excuse like this.

  8. mostlymac says:

    meh, I prefer acoustic triggers. but the pressure plate would be good for something that’s silent.

    Course, nowadays, most people just use high speed cameras to capture everything then pick out their favorite stills later.

    Regardless, it’s always amazing to be able to see things that happen too fast for the human eye to detect.

  9. Nomad says:

    Hm i bet it would be a lot easier to trigger a camera (read: DSLR) via the remote shutter release port. And it would have other advantages e.g. you could use a better flash instead of that crappy one built into disposable cams.

  10. Jonathan says:

    Aah, finally a way to document proper technique for Self-defense Against Fruit!

  11. biozz says:

    MY FIRST HACKADAY!!!!

    @Nomad it covers in the description the use of both an SB-600 and the cheap flash and why i chose a cheap flash over the sb-600

    @blodgar no all i had on hand was a peach XD … i wanted to use an apple

    @Bob you need to wait for you to regain your natural night vision

    @Entropia i have played arround with using an arduino but for sound trigger i would use a preamp and an opamp with a 555 but an arduino or AVR would be much easier!

  12. Colin Brown says:

    To all the people suggesting that this project would be better if the camera was triggered via the remote shutter release – the response time of the camera will not be sufficient. The flash power can be turned down to give an extremely small exposure time. In fact, some people have used that technique to capture speeding bullets.

  13. biozz says:

    @Jonathon Miller
    i have a hacked D90 shutter cable (i made for this instructable http://www.instructables.com/id/Nikon-D90-MC-DC2-Remote-Shutter-Hack/ ) the problem is that there is a noticeable delay from when the signal is sent to when the exposure is taken … you can try it by replacing the flash with this shutter cable and accept the delay but i think the best way is to create a delay and slow shutter speed (i used a JJC TM series nikon D90 shutter remote but a time delay with internal delay function and an exposure of a secound or so will work) works great … get ready when it beeps and when you hear the click hit it

    for any one looking to do this in one shot this is what i used

    Camera: Nikon D90
    Mode: Manual
    Shutter Speed: Bulb (3 second external trigger a 3′ shutter is equivalent)
    Aperture: F5.2
    ISO: 250
    White Balance: Flash (about 6500K)
    AF: Off

  14. Quin says:

    This is a nice hack, built on a solid old film technique. I wonder what the cause of that long of a delay in the SB600 is. It should be snapping as soon as you short the two contacts together; I don’t think the 600s have an flashbulb type sync mode. I think I need to see what the delay on my 285 is now.

  15. Jon says:

    Everyone is wondering why they are triggering a flash instead of the camera. Let me explain. The fastest shutter speed on most dSLR cameras is 1/4000th of a second. With my setup, my Vivitar flash allows me to get the equivalent of a speed of 1/30,000th of a second. A flash of light has the ability to last much shorter, than the duration that is required to mechanically open a shutter. It may be possible to take some high speed photos at a speed of 1/4000th, but then the problem of latency comes into question. When working with speeds upwards of 1/5000th of a second, latency is a huge problem. This picture http://flic.kr/p/8b2ULF shows a shutter speed of 1/30,000th of a second. Lower speeds are more acceptable when dealing with fruits and the like, but breaking glass requires upwards of 1/10,000th of a second, to prevent blurring.

    More pictures at 1/30,000th http://www.flickr.com/photos/whosdadog/sets/72157620083247995/with/4708034967/

  16. Sparky says:

    It would probably be best to work with a red light, because (I think) red doesn’t spoil your nightvision. Of course, you should turn off the red light before opening the shutter.

    I’d think the relay would introduce a fairly significant delay, because most mechanical relays take between 50 and 100ms to actually switch. A solid-state solution would probably have a much shorter and more predicable delay. A simple MOSFET or BJT could do the trick, or a decent optocoupler (possibly with a darlington output) could solve any headaches with the input signal to the flash unit if it doesn’t have an active-low input.

  17. PKM says:

    I made something similar for my first Instructable- it used card and foil for the pressure plate but was otherwise similar, you can see it at http://www.instructables.com/id/Minty-Strobe/

  18. biozz says:

    @sparky

    i covered the pros and cons of using relays vs an SCR (a mosfet or a bjt would be impracticable)
    i get MUCH faster response times with my relay than you say here and i have yet to experience any noticeable delay at all doing everything from fruit smashing to glass cracking and i estimate a delay of about 5-10ms and can probably get lower with reed relays
    i concluded that using a small relay is perfectly practical and an easier and safer alternative to and SCR and going online and paying $8 shipping on a $1 part and waiting 5 days for it to be delivered was unnecessary

    @Quin
    after farther screwing around i found out that the response time of an SB-600 flash is 1/2000th of a second at most and 1/400th practical (according to a forum) it might have to do with the signal having to pass threw all of nikons advanced CLS circuitry … maybe its sending or waiting for data … idk but it is a delay but i will still be looking in to using it and looking in to other ways of triggering it that may improve response time but for now this cheap flash unit works best

  19. Olivier says:

    For this kind of pics, I’m using CHDK for canon cameras.

  20. Quin says:

    @biozz
    for remote firing the 600, are you using a fully connected shoe? All the points on the flash going to all the points on the camera, and so on, or just shorting the, iirc, the center pin to the shoe itself? Can’t make that out from the pictures of the shoe on your page. And I don’t have access to a SB600, does it do it’s own light metering or is it full manual? I mean, 1/400 is enough time that if you were firing it from an optical trigger, by the camera’s built in flash or another 600, you might end up with only half the frame exposed. I can’t see how that would pass QA, or not cause a revolt by the hoard of Nikon shooters.

    really wishing I had a scope, to see what the difference in delay is when shifting my 5600 and 285 from sync cable, to hot shoe, to wireless and optical trigger; and seeing what the varistor does to the equation.

  21. biozz says:

    @Quin
    its the center pin shorted to ground to make it trigger
    it has a manual and TTL modes … 1/260th of a second is FAR more than whats needed for photography so im not surprised on what would be for highspeed photography a long delay … but im going to continue work on it to measure the delay

    i have a scope i just need to rig up a photo transistor to test it but currently i have my plate full
    im probably going to end up building my own adjustable flash unit if i cant get this sb-600 to behave … i just need to figure out how to do that ^^;

  22. NathanF says:

    A few comments:

    1) Great work to the guy that made it (it is very clever.) But as others have said, an acoustic trigger can do everything that this can do with 1/10th the complexity, and without the limit of it having to be underneath the object. HiViz.com has a kit to do it for $20, for instance. It has a microphone that you can vary in sensitivity to fire the flash based when it detects the sound of impact. Also a built in variable delay.

    2) As some others have also hinted, there are two reasons a device like this triggers the flash and not the camera:

    a) The duration of a flash firing can be set nearly an order of magnitude smaller than that of a shutter on even a professional SLR camera. That being the case, you will always be able to stop more motion with a flash fired in darkness with the shutter already open compared to setting your highest shutter speed on the camera and triggering the camera directly.

    b) On most cameras, there is a delay between the time you send the signal to open and close the shutter and when it actually happens.

    For those two reasons, the flash method is universally used (unless you have some crazy fast, expensive high speed video camera) to stop super fast motion like bullets firing. It has many drawbacks, but it works.

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