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Thread: Connecting 2 circuits to one relay?

  1. #21
    Maximum Bitrate KyleYankan's Avatar
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    Blah! OK, you made me realize my mistake in vocabulary. triggers != sources. Ha.

    I wanted two sources to connect to one relay to activate the relay. I know the relay coil's rating, but not offhand. I guess all I need to do is go out there, run the ACC line and hook it up.. Thanks.

  2. #22
    FLAC shakes's Avatar
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    right ... in relay terms I see a trigger as the signal that activates the coil ... and the source as the larger power source that the coil allows to flow.
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  3. #23
    Maximum Bitrate KyleYankan's Avatar
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    Erp, then I had it right. :-P

    Let me describe the problem. I have a relay I need to trigger when either A) ACC line is on or B) 12V from computer is on.

    How do I connect?

    Solution:

    DIODES!
    ___ / ------|<------- ACC
    \-------|<------ 12v+

  4. #24
    FLAC shakes's Avatar
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    yes ... we're saying the same thing ... you could use the diode option you have there, and feed the output of the diode to a SPST (Single Pole, Single Throw).

    You could also use a SPDT (Single Pole Dual Throw) without the diodes. SPDT has two coils (you'd connect ACC to one, +12v to the other) and has one source. So activating either coil will activate the relay.

    And again, you could achieve the same effect by using a DPDT (Dual Pole, Dual Throw). Again, two coils, but this time two sources. So by tieing the proper pins together you can turn that DPDT into a SPDT and use the solution above (with more possible current).

    What have we learned? You've got options :-)
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  5. #25
    Maximum Bitrate KyleYankan's Avatar
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    Well - to be honest I've never heard of a relay having two coils. Mine are usually spring loaded. NC and NO positions. I'm sitting here with a soldering iron and a relay, with some solder, and these here diodes. Getting ready to do the original schematic I saw. One alst question - the end of the didoes w/ the white bar --- goto the positive or Vcc? Towards the ACCA nd the 12V right? Just ran the ACC wire. Thanks.

  6. #26
    Maximum Bitrate mushin's Avatar
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    Quote Originally Posted by shakes
    You could also use a SPDT (Single Pole Dual Throw) without the diodes. SPDT has two coils (you'd connect ACC to one, +12v to the other) and has one source. So activating either coil will activate the relay.
    Eh?? An SPDT gives you two contact paths (as opposed to a SPST that switches between a contact and no-contact. It doesn't apply to relays, but switches can also have SPxT, where x is the number of positions.) In either case, a relay only has one coil.

    I can't do good ASCII art, and I don't want to explicitly poach another sites graphics, so I give you Google Images :

    SPST
    SPDT
    DPST

    The green on black images illustrate it quite nicely.

  7. #27
    Maximum Bitrate KyleYankan's Avatar
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    Mushin: I understand that. Here's a quote from a previous post: "SPDT has two coils "

    Anyways - I just realized I needed to go with relays. My dumb.
    *builds circuit*
    *plugs it in*
    *tests it*
    *unplugs circuit goes to old way*
    I guess I'll just get the relays tomomrow from mechanice friend before work. Thanks for the help though

  8. #28
    FLAC shakes's Avatar
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    Quote Originally Posted by mushin
    Eh?? An SPDT gives you two contact paths (as opposed to a SPST that switches between a contact and no-contact. It doesn't apply to relays, but switches can also have SPxT, where x is the number of positions.) In either case, a relay only has one coil.
    hmmmm ... yes yes, you're right.

    guess I myself was getting confused between Poles and Throws.
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  9. #29
    Raw Wave shotgunefx's Avatar
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    Quote Originally Posted by KyleYankan
    Well - to be honest I've never heard of a relay having two coils. Mine are usually spring loaded. NC and NO positions. I'm sitting here with a soldering iron and a relay, with some solder, and these here diodes. Getting ready to do the original schematic I saw. One alst question - the end of the didoes w/ the white bar --- goto the positive or Vcc? Towards the ACCA nd the 12V right? Just ran the ACC wire. Thanks.
    Don't you want a DPST relay ?

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