Confused on DPDT switch

Discussion in 'Gen 2 Prius Accessories & Modifications' started by jcnichols, Aug 13, 2008.

  1. jcnichols

    jcnichols New Member

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    Well, I've been reading, and reading again, all the excellent posts on putting in a switch to temporarily disrupt the NAV and/or BT wires.

    I can see doing 2 switches, and being able to interrupt one or the other, but I'm lost as how to do it with a DPDT switch. In such a switch, would the "up" position interrupt the NAV wire, while the "down" position would interrupt the BT wire? Or are both the NAV and BT wires interrupted together?

    I'm probably "overthinking" this, but I would like to use a single switch to be able to interrupt either the NAV or the BT separately, and have the "normal" mode be the "neutral" position on the switch. Is that possible?

    Thanks.

    Jeff
     
  2. efusco

    efusco Moderator Emeritus
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    DPDT would affect NAV in one direction and BT in the other. The only advantage is that you'd have one switch instead of 2.
     
  3. jcnichols

    jcnichols New Member

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    Ok, thanks for the info. I think I have the understanding backward--the switch will BREAK the connections, not MAKE the connections, right?

    I real DOH! moment.

    Jeff
     
  4. jcnichols

    jcnichols New Member

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    Ok, thanks for the info. I think I have the understanding backward--the switch will BREAK the connections, not MAKE the connections, right?

    I real DOH! moment.

    Jeff
     
  5. efusco

    efusco Moderator Emeritus
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    Correct, the circuit is normally closed...you break/open the connection to disrupt the speed sensor signal temporarily to allow you to access those features that are locked out when the speed sensor tells it you're moving.
     
  6. jcnichols

    jcnichols New Member

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    Thanks again for the clarification.

    Ok, one (hopefully) last question: Should I get a DPDT with a center "off" position? Or, as I've seen in the discussions, once I've broken, say, the NAV speed wire, it "resets" in about 30-60 seconds, but if the switch is still in the same position, does the NAV just rely on the GPS signal?

    I guess what I'm trying to determine (besides the wiring of the switch itself) is how to ensure that both the NAV and BT wires are in the closed position. If the DPDT switch is "thrown" in either direction, then one of the circuits would always be open, right? (even if the NAV speed wire then "defaults" back to the GPS signal) That's why I thought a center "off" position would be ideal, but the pictures I've seen here in PC don't show that type of switch.

    Sorry to be so dense on this.:confused:
     
  7. efusco

    efusco Moderator Emeritus
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    Yes, you definately want a center "OFF" position.
     
  8. David Beale

    David Beale Senior Member

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    Be careful what switch you get. Some with a centre position are made so that one side doesn't switch when put into the centre position when the toggle is moved in one direction and the other side doesn't switch when put into the centre postion when the toggle is moved in the other direction. This allows the switch to be used as a SPTT (three position single pole).
     
  9. jcnichols

    jcnichols New Member

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    Well, I picked up a DPDT mini switch (with a center "OFF" poisition) from RadioShack and got out my trusty multimeter to see how the connections are made.

    In my diagram, I numbered the 6 connectors. When the switch is in the center, or "OFF" position, as expected, there are no connections between any combination.

    In one of the positions (lets say UP), pins 1 & 3 are connected, as are pins 2 and 4. In the DOWN position, pins 3 & 5 are connected as are pins 4 & 6.

    So, what I can't see is a way to have both the NAV and BT wires work independently. To have them both closed, the switch would have to be in the UP or DOWN position, with the wires connected to the appropriate pins on the switch. If I move the switch to either the center of opposite position, then BOTH speed wires would be disconnected at the same time.

    While this isn't a bad thing necessarily, I would like to be able to disrupt the NAV while keeping the BT connected and vice versa, and of course have a position where both NAV and BT speed wires are closed and functional. What is so confusing is that I can totally see how to do this with two separate switches.

    And do I need a load (voltage source) on the switch? I've seen some diagrams, but many of those control a load or power something or reverse a motor polarity.

    Thanks again for any help with this--I actually do understand some electronics and have even built a timing board in my laser research, but we didn't need switches (thank goodness!).
     

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  10. jcnichols

    jcnichols New Member

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    Re: Confused on DPDT switch--found a solution

    Well, given enough time I can usually figure some things out ;)

    If I connect pins 3 & 5 together, and pins 2 & 6 together, then I can have the following situations:

    NAV on, BT on ("normal" setting)
    NAV off, BT off (in the middle "OFF" position)
    and
    NAV on, BT off

    It's not exactly what I wanted (I would like the 4th option of NAV off BT on) but it will work for what I want.

    Thanks for everyone's patience as I worked this out. Going to cut some wires tomorrow! :eek:
     
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