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Thread: Wiring dilemma

  1. #1
    Variable Bitrate
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    Wiring dilemma

    My situation is I made a navigation bypass button by interrupting the signal to the headunit from the parking brake and the speed sensor. The problem is I'm not seeing how to connect an indicator light to it to let me know the bypass is activated. Simply attaching the light to the button, I believe, wont work due to the nature of the functions...I believe the signal would be intermittent based on what would be happening. The brake pressed - signal, depressed - no signal; accelerating - signal, stand still - no signal. So I believe the light would be blinking on and off regardless of which way the button is flipped. And then I dont want to introduce power to the button because I dount want to mess up the headunit or components. Any ideas on how I can achieve what I'm after?

    If seeing the hack can help, you can see it here with instructions with the pics: http://www.freshalloy.com/forums/sho...light=nav+hack . Pic 12 and 19 I believe are the most important.

    Hopefully this made sense.

  2. #2
    MySQL Error soundman98's Avatar
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    i was going to recommend a dpdt switch, but it looks like your already using one to control both functions...

    in that case, then i believe a triple pole, double throw switch would be best--this one looks closest to what was recommended in the how-to:
    http://www.mouser.com/ProductDetail/...CyMWSpsqeCc%3d


    that way, you can switch the leads shown in the how-to via 2 of the poles, reserving the last pole for your 12v light.

  3. #3
    Raw Wave
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    Their one off price of $67.38 worried me a bit...
    (Obviously it should be $6.74, but will you be refunded?)


    PS - no ns in dilemma (as I recently learned!).
    Last edited by OldSpark; 03-26-2012 at 10:58 AM. Reason: PS...

  4. #4
    MySQL Error soundman98's Avatar
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    wow, didn't realise those switches are $50 ea...

    ok, option 2:

    a spst switch--if it's lighted, you only need one dpdt relay(this would serve as the switch in the how-to), if you want the indicator somewhere other then on the switch, then just connect the indicator to the output of the switch-- this option should be less then $15..

  5. #5
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    Sorry, could you explain that a little different please? I dont exactly understand what you're saying.

    But from you mention a relay, isnt that with the assumption that there is current coming out the headunit? If there is that assumption, and if there is current, then I wouldn't be in the need of a relay or have this dilemma, I could just connect the indicator to the switch. No?

  6. #6
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    Quote Originally Posted by soundman98 View Post
    wow, didn't realise those switches are $50 ea...
    And holy crap Batman, I was only kidding - they ARE ~$50 each! I thought it was a misprint.



    But google 3PDT or 4PDT for lots of switches under $10...


    However IMO a plain common switch that controls (3PDT etc) relays is often best whether it be to remove heavy loads from switches, or to relocate the masses of wires (for easy access when they break),
    And those relays often have sockets hence a simple plugin replacement if the relay fails (which is rare).
    (Not that socketing of components including relays is recommended for vehicle use (vibration & socket contacts), but IMO it's better than soldering the relay.

  7. #7
    MySQL Error soundman98's Avatar
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    yes, that's what i get for posting stuff without looking at the price...

    Quote Originally Posted by Champak View Post
    Sorry, could you explain that a little different please? I dont exactly understand what you're saying.

    But from you mention a relay, isnt that with the assumption that there is current coming out the headunit? If there is that assumption, and if there is current, then I wouldn't be in the need of a relay or have this dilemma, I could just connect the indicator to the switch. No?
    so basically, the switch will control a +12v wire that activates the relay, and the relay becomes connected like the how to. that way, you can get your switched voltage to light up the indicator without fudging up the headunits circuits. it really jsut adds 2 wires the to the circuit-- a +12v switch lead, and ground.

    like this:



    oldspark makes a good point though that with the relay method, you would have a lot less wires to run-- ie, just run 2 wires to the switch location(positive wire, and the wire going to the relay), and then the relay can be located elsewhere.

    but in case you are still interested in the 3pdt method, it looks like most of the switch options are toggles instead of rocker switches:
    http://www.google.com/search?q=3PDT&...w=1680&bih=859

  8. #8
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    Now that's a good listing of (3PDT) switch options.

    It should be implicit that the relay(s) can be located remotely - eg, to shorten high-current conductors (headlights, fans, etc) or to "remove" noisy relays.

    And with relays, it's easy to change the switch or controlling circuit - eg, 3-pos toggle to rocker, or 2 switches, or a uPC or FusionBrain etc.


    But $50 for a switch!!? That demonstrates one reason for avoiding high-current switches!
    Besides, running high currents thru switches (say >3A-5A; definitely 10A) is IMO a limited lifespan and a warm-becoming-hot switch.

  9. #9
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    Yeah, a $50 switch is not happening lol, it isn't that serious. I understand how the relay works, you supply power/signal and that will bridge a connection to activate something else, but I don't understand the implimentation here.

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    What are you saying should be used to activate the relay? The ground wire off this switch?

    The way I'm invisioning what you are recomending is to take the ground wire from this switch and send that to the relay and from the relay to ground because you feel there is some signal there. That would cause the circuit in the relay to close which would have a 12V line attached at one end and the indicator on the other end. Is that what you are recommending?

    If that is the case, isn't the whole relay thing redundant? Because if there is signal to activate the relay through the ground wire from the switch (which I can't see because that line is coming out the headunit), wouldn't that be enough power to activate a simple indicator?

  10. #10
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    Relays. Two parts:

    1. The contacts:
    A collection of contacts (or switches).
    Simplest is on-off (SPST).
    Common is "changeover" (SPDT) which can be used as on-off (don't use the extra contact/terminal).
    Other multi-contact and switching arrangements exist.
    Relay ratings like 30A, 200A, etc refer to contact ratings - ie, what current they are rated for and at what voltage (50VDC, 250VAC etc - NOT to be confused with coil operating voltage!).

    SPST & SPDT mean "Single Pole, Single Throw" & SP Double Throw" respectively.
    "Pole" means the number of circuits.
    "Throw" means positions, but don't confuse Position's P with Pole!
    And Throw for switches means electrical positions, ie, an SPDT switch may be center off - ie, on-off-on, but that isn't relevant for relays which can only be in an energised else de-energised state - IE, the relay is either on or off (again, not to be confused with what its contacts are doing...).
    Double becomes 3, 4, 8 etc for multi-pole relays/switches. (And plain relays are either ST or DT.)


    2. The coil (aka solenoid):
    The coil actuates or pulls in the relay contacts.
    The coil can be rated for 12V DC operation, or 110VAC, etc.
    The coil has a resistance (aka impedance) which determines its current at the rated voltage. (From V=IR, and P=VI where "coil power" is defined.)

    DO NOT confuse coil voltage & current with the relay's "rated" contact voltage and current.
    A 12V relay rated for 30A @ 60VDC & 40A @ 250VAC is a 12V actuated (coil) relay whose contacts can switch up to 30A at up to 60VDC, or up to 40A at up to 250VAC.
    And never use a relay for a voltage for which it is not rated. (And AC & DC have different impacts.)


    1 + 2 = 3+:
    The upshot of the above...?
    Isolation - ie, between trigger source and output. A 12V DC device can control 110VAC appliances via a relay. (WARNING - Legislation refers, and life-saving knowledge is essential!!) Also isolation between circuits - maybe because of different voltages or ground, or to separate noisy or dirty from "clean" circuits.
    Amplification - ie, a small current can control a big current. EG - a small headlight switch can turn on 20A and more of headlights.

    Common uses:
    - to make low power things able to switch high power - eg, uPCs or PCs or circuits to control heavier (or unknown current) appliances.
    - to shorten high-current (or voltage) wiring. EG - heavy headlight wiring from battery via fuse & relay to lights; only the thinner low-power switch-to-coil wire needs be long.
    - to change "sense" - eg, a GND switch to activate +12V lights, or invert a voltage signal (+12V to GND, or GND to +12V etc).


    The main relay rules are:
    • Match the relays ratings to the input voltage and output voltage/currents.
    • A "spike prevention" diode may be required externally across the relay's coil (to prevent damage to electronics).
    • Ensure the control circuit or switch can handle the relay's coil current. (Spike protection refers for electronics.)
    • Beware of environment specs - dampness or wetness; sparks; vibration; temperature.


    FYI "Normally" as in normally open (NO) or normally closed (BC) means unpowered, or as it would be in a shelf. Not to be confused with "but it's normally tuned on!")


    I like relays to ensure maximum power/voltage is delivered to high-power loads, but more because I can chose almost any (plentiful, lit/unlit, cheap, small) switch I want and the relay or relays handle the switching currents or switching complexity (an on-ff SPST switch control a 4PDT relay...)


    Relays are probably the simplest "interface" device available to DIYers etc. And often the simplest way to improve or solve performance issues (eg, remove noise, improve lighting or amplifier outputs).
    Well worth getting your head around...


    PS - that switch's GND is probably for a lamp, hence unsuitable. But you'd be using its other contacts for a relay.
    Last edited by OldSpark; 03-27-2012 at 02:27 AM. Reason: Spellinks, & FYI "Normally"... and a later PS

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