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More questions on remote control of cameras

Discussion in 'Hobby Electronics' started by L.A.T., Aug 15, 2008.

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  1. L.A.T.

    L.A.T. Guest

    Helped by comments from posters to this newsgroup, I have made three Jaycar
    flexitimers to switch on InfraRed remote controls to cause Canon G2 cameras
    to take one exposure every ten seconds. . They are made by butchering cheap
    I.R. remote controllers from Hong Kong (ebay) and having the flexitimer
    relay close the appropriate switch.
    They work well.
    They are also a bit of overkill. 12Volts to activate a solenoid to switch a
    milliamp or two at three volts maximum.
    There must be a simpler way.
    A long time ago I built, from a circuit in E.A. (I think) a timer to switch
    on and off an EPROM eraser. It had a 555 and a few other bits and the timed
    intervals were adjustable.
    There must be a similar circuit somewhere to do exactly what I want, which
    is to close a circuit so that the I.R. is activated, (always for one second)
    and then turned off for ten seconds. I believe it would not need a relay
    because the device being switched has such low current.In other words, I
    believe the switching transistor would be able to handle that sort of
    current and voltage.
    The ability to alter the off time from, say, six seconds to twenty seconds
    would be an added bonus.
    Can anyone point me in the right direction?
     
  2. Phil Allison

    Phil Allison Guest

    "L.A.T."

    ** If you drive a few mA into the base of a BC547 or similar - the
    collector to emitter resistance falls to a low value and will act as an on
    switch.

    An LM555 will operate from 5 volts DC, so a 2.2kohms resistor from pin 3 to
    the base will do.

    Up to you to work out the rest as we have no details on those RC units.


    ...... Phil
     
  3. L.A.T.

    L.A.T. Guest

     
  4. The simplest option (from a component point of view) is an 8 pin
    PICAXE chip.
    http://www.rev-ed.co.uk/picaxe/

    Probably no need for any other components as the output pin could be
    configured as an open collector (switching between output LOW and
    input if needed) that could likely be connected directly across your
    IR remote switch.

    The PICAXE works down to 3V, so you could probably power the IR remote
    and PICAXE from the same battery supply.

    A DIP switch on the other pins could select the desired time period if
    needed.

    No real software skills needed either, PICAXE's can be programmed with
    flowcharts if desired.

    Silicon Chip have published countless articles on using the PICAXE.

    Dave.
     
  5. Franc Zabkar

    Franc Zabkar Guest

    There is a 3V version of the LM555, eg the TLC555:
    http://focus.ti.com/lit/ds/symlink/tlc555.pdf

    Depending on how the IR remote's contacts are wired, you may be able
    to switch them directly from pin 3 of the 555, or via an inverting
    transistor, or you may need a CMOS analogue switch, eg CD4066 or one
    of the many modern alternatives.

    See http://www.maxim-ic.com/appnotes.cfm/appnote_number/638

    - Franc Zabkar
     
  6. Jasen Betts

    Jasen Betts Guest


    what happens if you short-circuit the remote button and switch the
    power to the remote on and off ?


    if that doesn't do anything useful here's some other ideas.


    use the 555 to drive a mosfet power the whole lot from one of those 9v
    batteries,

    +9V--. |-------> to remote
    | || mosfet
    555 -----'|---+---> to remote
    | |
    0V--+------------+

    you probably won't be able to power the 555 and the remote from the
    same supply


    or you could try wiring a LDR across the remote contacts and
    blinking a LED at it. (wrap both components in black lightproof tape)
    then you may be able share the supply

    (or a phototrasistor based optocoupler may work instead of the LED+LDR)

    given that the remote wants a 3v supply a TLC555 may be a suitable
    timer for these options (as they are isolated you can share the supply)

    Bye.
    Jasen
     
  7. L.A.T.

    L.A.T. Guest

    "snip>
    That was one of the things I tried. It seems that the transmitter must be
    powered up all the time.
     
  8. JohnS

    JohnS Guest

    I'd be inclined to tackle the problem differently.
    I would record the code from a remote control device that actually
    works and then reproduce this waveform.

    To record the waveform I would use an IR decoder as an input to an
    Atmel or PIC.
    I would set the inbuilt timer to interrupt every millisecond.
    On every interrupt I would compare the state of the input (0 or 1) to
    it's previous state.
    When there is a change in state, I would save the state and time in ms
    to memory.
    You don't really need to save the state as you know it will be
    inverted every transition.
    As a guideline, the RC5 code is 14 bits so there would be about 28
    transitions to record.
    The total time for the code is approximately 25,000 ms so you would
    need to store 2 bytes for each transition.
    The millisecond counter would be set to zero on the very first
    transition.

    Allow about a second from the last transition and then transmit this
    information back to a PC via an RS-232 cable.

    With this information you can reproduce the waveform.

    You would probably gate this with a 36khz square wave and drive an IR
    LED with it.
    Or you can create these in you microprocessor chip.
    That way you can use you PC to send commands to the PIC which then
    sends commands to your camera.

    Once you suss out the control waveforms you can control the camera at
    will.

    Hope this helps.
     
  9. Jasen Betts

    Jasen Betts Guest

    this gives upto 1ms jitter so the signal rate had better be well below
    that...
    it might be a better move to set up an interrupt on the change-of
    state of the input pin and use input capture to snapshot the clocks
    accumulator, that way you get much better precision in your timestamps
    for the signal edges.
    25 seconds? - seems kind of long!

    25 miliseconds? - you'll not detect 28 edges if you sample every
    millisecond

    250 miliseconds is believable,
     
  10. L.A.T.

    L.A.T. Guest

    This is pretty much what I am doing. I bought half a dozen similar devices
    for $1.90 each. They have a little circuit board with a chip and a couple of
    components and membrane switches to select which function the chip will
    perform. I take off the membrane and cut a track or two and solder a couple
    of wires so that the picaxe acts as a timer and then as a switch.If I can
    find out what the pulses the on-board chip generates, I can do away withe
    the circuit board and have the picaxe generate the pulses. Then the whole
    thing will fit into a Dick Smith switched battery-holder together with its
    batteries
     
  11. JohnS

    JohnS Guest

    ----------------------------------
    You're right.
    The timings I quoted were incorrect. I was just answering without
    digging out my code and checking it.
    My actual project was a bit different. I knew my codes and timing and
    just sampled the centre of each bit to see if it was a 1 or 0
    The correct timing and more info on IR codes can be found on the web
    by googling "RC5 Remote Control"
     
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