mechanical relay vs solid state

Discussion in 'General Electronics Chat' started by Andreas, Oct 25, 2010.

  1. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    Hi,
    I have an off the shelf Sony camera remote controller which works with the LANC protocol. The record button on it has two contacts (after all it's just a pushbutton). I want to push this button electronically with a 10 volt pulse of around 100ms duration.

    I was considering using a solid state relay (for it's low operating current and high switching speed) but realise that these devices, like optocouplers with open collector outputs or even mosfet types will require some current to flow at the output for it to work properly (I assume otherwise the outputs are left esentially floating open).
    Naturally, I don't want to impose any currents or voltages into a circuit which I have no shematic for and fear damaging it or the camera!
    Would a mechanical relay still be the best choice in this case as its outputs are completely isolated from the input and need no pullup resitors or anything on their output side?

    What about the Analog Devices ADG452 series of chips for such an application? Thinking about it. I guess the pushbutton on the remote controller when closed must have current flowing through it so the ADG452 might just work OK. I may have answered my own question here.

    Tnx
     
  2. mbohuntr

    Active Member

    Apr 6, 2009
    413
    32
    Opto couplers are designed for just such a situation. They isolate control voltages from the circuit preventing damage....
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    measure the voltage at the open contacts, then switch meter to current mode, and see how much current flows through the circuit when the contacts are closed.

    This would be good information to have in any case, but knowing the polarity of the voltage, and current use would help with the decision.

    As long as it isn't a "push halfway to focus, all the way to take picture" type switch, this should be fairly straightforward.
     
  4. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    1. Firstly, it is a video camera REC push-button so no 1/2 way down focus etc...

    2. I measured the voltage at the contacts and get 3.28V (let's call it 3.3V which happens to be a nice CMOS SMD voltage level).

    3. I am not entirely sure if you mean, "switch meter to current mode" in situ (like the voltage reading or... see point 4.) In any case I did this and the camera went straight into record mode (I imagine it sees the current meter as a suitable path for the current to flow). Anyway for what that was worth, the result was 0.1mA.

    4. I would have thought that to measure operating current, one needs to actually break into the circuit so that the current meter is actually in series with the circuit under test.

    5. I am thinking now that a simple 4-pin optocoupler (as mbohuntr suggested) could do the trick. Where the output has only an emitter and a collector. I'll stick a small resistor (33R) in series with the collector just to be safe. What do you think of this approach or would you chose a mosfet type instead?

    Let me know if you have any more thoughts, else, thanks for your help.

    A
     
  5. Andreas

    Thread Starter Active Member

    Jan 26, 2009
    68
    4
    P.S. Point 5. - better make that reistor 330R as the opto's collector current is maximally rated to 50mA (spec sheet recommends 10mA).

    A
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    The reason for measuring the voltage was to find out the polarity and level, and the current measurement was to make sure it was a very small load. The meter in current mode across the two contacts should have made it record, as it was nearly a short.
     
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