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555 timer DSLR time lapse shutter release

Discussion in 'Electronic Basics' started by Dave, Feb 21, 2007.

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  1. Dave

    Dave Guest

    I've tried to use a Velleman timer kit for time-lapse photography with
    my Pentax DSLR camera but the single relay output isn't enough.

    The Pentax-made *manual* cable release is terminated in a standard
    2.5mm stereo jack plug. When the button is pressed, the centre contact
    on the plug is shorted to the one nearest the body (triggering
    autofocus etc) and when the button is pressed further in, these two
    contacts remain shorted but the contact furthest from the plug's body
    is then also shorted to trigger the shutter release.

    What's needed for the 555 time-lapse circuit is second relay whose
    Normally Open contacts close as well, a fraction of a second after the
    first one. All 3 connections were shorted at this point when I checked
    the manual cable release with a continuity tester.

    I've considered adding a single transistor triggered by the 555's
    output but with a simple RC time delay, e.g. its base taking a finite
    time to reach a sufficiently high voltage to turn the transistor on,
    and consequently activating the relay.

    I'd be grateful for any suggestions to achieve this result. It's been
    years since I've done much with a soldering iron and electronic
    construction. Maybe I should be using a thyristor instead of a
    transistor, or a Darlington or something. I want to keep it simple.

    Thanks in advance, Dave.
    <http://www.henniker.org.uk> 3000 photos especially
    Edinburgh & Scotland. + 3D rendered art, old ads etc.
    Délété david for email; watch the spam filters.
     
  2. John Fields

    John Fields Guest

    ---
    I'm not sure that's such a good way to do it because it won't
    unshort the contacts in the same sequence the manual cable release
    would. The way I'd do it would be to use a window comparator and
    drive it with an RC which would be driven by a 7555. That way, the
    last comparator that turned on would be the first to turn off and
    the 7555 would supply the charge and discharge path though its
    totem-pole output.

    If you like I can draw you a schematic, but I'll need to know:

    1. What's your supply voltage.
    2. What are you using to trigger the 555
    3. How long is the entire shutter release sequence?
     
  3. ehsjr

    ehsjr Guest


    I'm not sure what your velleman kit does. Presumably this:
    ------------
    | |
    ------- --------- (autofocus etc)
    T0 T1 T2

    And you need this?

    ------------
    | |
    ------- --------- (autofocus etc)
    T0 T1 ---- T2
    | |
    ----------- ------ (shutter)
    T0 T1a T1b T2

    In the absence of any specs, and if you have
    a bunch of relays, you could try this:

    Vellman
    Relay
    n/o Contact RY1-1 n/o RY1-2 n/o
    |>| |>| |>|
    +12 ---o o----+---o o---+-----+ +---o o---> auto-
    | | | | focus
    +-----+ [RY2] [D2] |
    | | | |a |
    [D1] [RY1] +-----+ +---------> Camera
    a| | + | | | common
    +-----+ [470uF] [10K] |
    | | | |
    Gnd ----------+---------+-----+ +---o o---> shutter
    |>|
    RY2-1 n/o

    When the Velleman relay transfers, it energizes RY1,
    which takes a few mS to transfer. When transferred,
    it energizes autofocus, and energizes RY2 through
    the charging current of the 470 uF cap. RY2 takes a
    few mS to transfer, which provides the delay between
    autofocus and shutter. When transferred, it activates
    the shutter. RY2 drops out when the 470 uF cap is
    charged and stops drawing current through RY2. The
    10K will discharge the cap when RY1 drops out.

    The circuit doesn't have a lot to recommend it,
    except that it will give you a few mS delay, and
    is "spec-less". It might work. You can try it
    until you develop specs for what is really needed
    for the timing.

    Ideally, it would be nice to have a circuit with adjustable
    times for T1 to T1a, T1a to T1b and T1 to T2 and
    that can be designed if we know the specs.

    Ed
     
  4. Lionel

    Lionel Guest


    Have you tried simply shorting both the center & tip to ground at the
    same time? Your shot will probably be delayed by however long it takes
    the AF system to achieve focus, but that'd be true with any other
    system as well. Alternatively, you could use a positive output from
    your 555 to drive the bases of 2 NPN transistors, with the collectors
    connected directly to the tip & center connections, & both emittors
    wired to ground.
     
  5. Dave

    Dave Guest

    I've copied the circuit diagram to:
    <http://www.henniker.org.uk/images/555timer-circuit.jpg>

    The supply voltage is 12 volts. There is no start button, just
    applying power starts it. The length of the shutter release sequence
    is probably roughly 1 second in manual use, whether using the cable
    release or the button on the camera, i.e. press the button half way,
    wait for autofocus / autoexposure to kick in, there's a beep to
    confirm it's focussed then you press the button all the way to open
    the shutter and take the photo.

    Thanks to everyone for their suggestions. I reckon I'll dig out my old
    'breadboard' and try a few things out...

    Dave.
    <http://www.henniker.org.uk> 3000 photos especially
    Edinburgh & Scotland. + 3D rendered art, old ads etc.
    Délété david for email; watch the spam filters.
     
  6. John Fields

    John Fields Guest

     
  7. Dave

    Dave Guest

    I think I'm on the way to a working circuit. The output of the 555
    turns on the first relay and also turns on an NPN transistor with a
    100K resistor as a collector load. This goes low and triggers another
    555 in monostable mode. After a delay of say, between 500mS and 1S,
    the second relay should close and fire the shutter.

    I've got the trigger working - and I *did* have the monostable working
    but I need to take a rest because of the need to keep changing my
    spectacles as well as using a jeweller's eyeglass. The eyesight ain't
    what it used to be. I'm glad I don't have to fix CRT monitors and
    laptop mainboards any more!

    Dave.
    <http://www.henniker.org.uk> 3000 photos especially
    Edinburgh & Scotland. + 3D rendered art, old ads etc.
    Délété david for email; watch the spam filters.
     
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