12 volt relays

Discussion in 'General Electronics Chat' started by Stearman, Oct 16, 2008.

  1. Stearman

    Stearman Thread Starter New Member

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    I would like to energize a relay to close the contacts for a one shot pulse, and when I de-energize the relay have it close the contacts for another one shot pulse. The pulse could be a few milliseconds.
    Is there such a relay? If so, what do I call it?
  2. KMoffett

    KMoffett Senior Member

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    This works. The pulse width depends on the value of the capacitor, and the resistance and inductance of the relay coil. I don't think you will get pulse widths of "a few milliseconds", since relay switching times are usually 100 mSec or longer.

    Ken

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  3. Bernard

    Bernard Senior Member

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    I have seen some high speed relays, but none as you describe. What is the nature of your pulse ? My take is: use two diffrentators [.1μF & diode,k to c], NO & NC relay contacts to free end of caps. Connect outputs to a diode OR gate [k's tied together and connected to 10kΩ]. To discharge caps connect 1kΩ from NO & NC to ground. With a voltage applied relay armature [ or switch ] energising relay, one pulse will appear at 10kΩ, when relay opens another pulse will appear. It's a start, sometheng to throw rocks at.
  4. mik3

    mik3 Senior Member

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    If you want fast pulses then use solid state relays. They are noiseless (acoustically), lot faster than ordinary ones and do not produce arcing (between contacts on ordinary relays).
  5. SgtWookie

    SgtWookie Expert

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    Mechanical relays and switches have "contact bounce" whether they're closing or opening. This can take quite a while to settle out - perhaps several hundred mS. Not sure what you're trying to do, but if you need clean on/off pulses, then you need to go for a semiconductor solution.
  6. Stearman

    Stearman Thread Starter New Member

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    I may have misled you with the "few millisecond" close time. The close pulse time is not critical.
    I'm switching an intercom on and off in an old bi-plane. The way the radio intercom works is that when you momentarily ground the intercom input it switches the intercom on. You then have to ground it again to switch it off.
    I would like to have the intercom on as long as I hold a spring loaded toggle switch on in the cockpit.
    I want to switch a relay to ground the intercom input with a pulse when I engaged the toggle switch and ground the input again with a pulse when I release the toggle switch.
    Thanks for all the inputs. I really appreciate them................
  7. SgtWookie

    SgtWookie Expert

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    I should've guessed via your login name ;)

    So, is your Stearman certified for type, or experimental?

    If it's certified for type, you should not make any changes from the original aircraft specifications.

    If you're experimental - well, there is some more leeway. However, this mod is certainly not something you would want to do to get your aircraft out of certification for type.

    Stearmans are wonderful aircraft. I am truly envious that you have one that's flyable. If there were some way I could afford one, I'd have one and be performing barrel-rolls, loops and Immelmans across the skies of Orlando.

    Basically, changing anything in your aircraft risks having it undergo a re-certification as an experimental aircraft. If you are currently certified in-type, you do not want to have this happen.

    Along with this, your joystick comm switch is likely SPST, which means that it will be extremely difficult to "de-bounce". I can only suggest to you in the most respectful way that you do NOT want that kind of distraction while you are aloft. If you should happen to get a "contact bounce", your comm may toggle quickly from on to off - and then while you're still holding the switch down, your comm is off. When you release the switch, then your comm is toggled on, and you'll be confused; how do I get back to my radio? If you get too involved in this, things could get bad quickly.

    If something happens on a flight, pilots are all too prone to forget that their primary function is to "fly the aircraft".

    I know that you want this modification - but from many years experience and with a great admiration and respect, I recommend against it.

    Odds are too great that problems will develop, and the curious pilot will wind up trying to troubleshoot in flight - forgetting that their primary duty is to fly the aircraft.

    Enjoy the aircraft for what it is; along with it's quirks. The closer you can get it to original specifications, the better.

    Yeah, it's old. But it's wonderful. Please preserve it for the next generation.

    Not many Stearmans around anymore.
    Last edited: Oct 17, 2008
  8. raybo

    raybo Member

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    you are describing an oscdillator. you can try using a cap to do that and a relay. sometimes it is called a buzzer.
  9. KMoffett

    KMoffett Senior Member

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    What?

    Ken
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