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Button Pusher for Time-Lapse Photography

Discussion in 'Misc Electronics' started by George, Jul 16, 2007.

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  1. George

    George Guest

    Button Pusher for Time-Lapse Photography

    This article is being cross-posted in:

    The related binary files are posted only in the .binaries group.

    In case anyone else might be interested for future reference, this
    is as-built documentation of a project previously discussed in these
    Remote camcorder controller 02 Jul 2007
    Switching +/-12V from 6/0V 12 Jul 2007

    My camcorder will take still pics as well as video, and it has a
    remote control. I wanted to send the remote's "Photo" signal to the
    camcorder at a regular interval so I could do what amounts to
    time-lapse photography. Earlier I considered more elegant ways to
    do this, but ended up just rigging up a button pusher for the

    The project was made possible by an item from my junque box - a rare
    Magnecraft open-frame relay, #W88KDX-2, which I used as a solenoid.
    The floating contacts travel just the right distance, and with
    enough force, to depress the button on the remote.

    Basically, the remote and the relay are mounted on a strip of wood
    which is taped to the tripod handle (the camera is mounted backward
    so its I/R detector can see the remote's I/R LED). The remote is on
    top, and the relay on the bottom, and the two are connected via a
    hole drilled through the wood strip. Materials used include
    popsicle sticks, a short piece of wire-wrap wire (it must be blue),
    masking tape, a right-angle mounting bracket, and a rubber band. A
    Dremel tool with a cutting disk was used to cut off the fixed relay
    contacts and to cut the slits for mounting the connecting wire.

    The drive electronics are on a breadboard, powered by 4 "C" cells,
    all of which just hang from the tripod. The circuit uses one TLC555
    timer to provide the interval between button presses, and an LM555
    timer to set the duration of each button press. A dipswitch allows
    selection of intervals ranging from about four seconds to over one

    Since the relay requires at least 12V, and a fair amount of current,
    I used a MAX232 chip to convert the incoming 6V from the battery
    pack to a much higher voltage the relay can use, and a large
    capacitor to store that charge between presses. The two-transistor
    coil driver was suggested by James in the .design group, but the
    resistor values are all my fault. Thanks to James and all the
    others there who helped me figure this out.

    I don't have a schematic drawing program, so I just drew it by hand
    and took a picture. I hope it's readable. If anyone has questions
    or comments, fire away.
  2. George

    George Guest

    You are correct that the MAX232 can't supply anywhere near
    enough current on a continuous basis. But over time it can
    charge up a capacitor with enough juice so that when the
    time comes to push the button, the accumulated charge on the
    cap can be dumped all at once through the coil, and that's
    enough to make it work for a short time.

    I use the Tx outputs of the MAX232, one high and one low, to
    charge the 220 uF cap, which process takes about three full
    seconds to complete after the previous discharge. You can
    watch the voltage across the cap ramp up with an analog
    voltmeter, just like the books say it should. At that
    point, it's charged to about 22V. And during that three
    seconds, the current drawn by the MAX232 is about 30ma
    maximum, which is pretty much in line with the data sheet.

    I have no way to measure how much current the cap discharge
    actually produces, but it's enough to pull in the relay and
    push the button for a fraction of a second, which is all I
    need. So basically, it's really all about doing a slow,
    low-current charge of the big cap, followed by a sudden,
    hi-current discharge.

    By the way, I don't think the 10uF caps make any difference.
    I used them because I had them and didn't have four 1uF's.
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