Cap as a time delay?

Discussion in 'General Electronics Chat' started by bugmenot7, Mar 3, 2014.

  1. bugmenot7

    Thread Starter New Member

    Mar 3, 2014
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    Let me start off by stating that I have no training in electronics.

    I have a small battery powered RF remote. I am attaching a NO switch. When the switch closes, the remote transmits. When installed, the switch will likely be closed for several minutes. I only want the remote to transmit for about 2 seconds when it's closed.
    I looked at time delay relays on Digikey and everything is too large and the cheapest--at $16--is more than I wanted to spend.

    Is there some way to wire a capacitor to the switch to make it discontinuous after the capacitor is fully charged? Should also mention the remote uses a single 12V (number 23A) battery.
     
  2. Rich2

    Member

    Mar 3, 2014
    52
    1
    Put an electrolytic capacitor in series with the relay coil, it will then only stay on while the capacitor charges ie a couple of seconds
     
  3. #12

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  4. bugmenot7

    Thread Starter New Member

    Mar 3, 2014
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    I must not have explained correctly: I looked at relays but do not actually have one, and am still not quite sure if I need one.

    According to the transmitter's datasheet I'd need to drop it below 8V (ideally as close to 0 as possible).

    Also due to my lack of electronics knowledge I don't know to use that calculator; all I know is the supply voltage and time.
     
  5. #12

    Expert

    Nov 30, 2010
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    What is this, "it" that you need to drop below 8 volts?
     
  6. #12

    Expert

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    From what I see, maybe you are thinking the power supply needs to go below 8 volts to stop the chip. That just makes them go unreliable unless you take that voltage way below 8 volts, so the "as close to zero" is the right answer.

    A good way would be to make /TE go high after 2 seconds.

    are we on the right page with each other now?
     
  7. #12

    Expert

    Nov 30, 2010
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    This was the first idea, and it will work.
     
  8. #12

    Expert

    Nov 30, 2010
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    Now it looks more like this is the way.
     
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