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Thread: Relay resistance when using joycon question

  1. #1
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    Relay resistance when using joycon question

    I'm taking the signal from the steering wheel and going through a relay and switch so im able to change the destination of the signal from either the head unit or the computer. I got the joycon, but before cutting up wires it occurred to me....maybe paranoia....that I may alter the resistance to the head unit by going through a relay. And once that happens I won't have control of the head unit anymore.

    Will my fear happen? The relay I plan on getting is:
    http://www.alliedelec.com/search/pro...x?SKU=70178841
    Or
    http://www.jameco.com/webapp/wcs/sto...0001_291507_-1
    (There is something else I need to control through this process, that's why it's a multipoint relay)

    If the resistance does change, will a variable resister like the following help in bringing the resistance back to what it should be?
    http://www.alliedelec.com/search/pro...3879#tab=specs

  2. #2
    Maximum Bitrate Mickz's Avatar
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    Relay contact resistance will not case a problem.

    BTW A variable resistor (POT) would not work if contact resistance was a problem in any case.
    Surface Pro 2 128GB portrait mode, Win8.1, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE. Previous Car-PC Project

  3. #3
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    I doubt the relay contacts would have much resistance. You could measure it before putting it in the circuit but I doubt it's more than an ohm or two.
    Actually, if you'd read the spec sheet for the relay the contact resistance is 10 mili-ohms or so little it's not worth mentioning.
    What I've read about steering wheel controls is that they are in the k's of ohms so it shouldn't be a big deal.

    Most steering wheel controls should be only two wire so you'd only need a DPDT relay.
    The relay from Jameco will use 75mah of current.

    Good luck,
    davidk

  4. #4
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    Ok, thanks. These relays contact resistances are 50 and 100 m-ohms....which I'm assuming is less than an ohm, which I guess is fine. The thing that had me worried was the coil resistance which was 160ohms. What is that then? Doesn't that have an impact?
    My button resistances are:
    Button 1: 990-1030
    Button 2: 323-337
    Button 3: 108-112
    Button 4: 0
    And then another 4 with the same resistance.

    I have a three wire system, plus something else I need to build into the relay, New relay switching needs

    How much affect will soldering have on the resistance? I've read somewhere here that the way someone did their soldering did affect resistance somewhere. So how do I solder the proper way as to not affect the resistance by much?

    Just for understanding sake, why wouldn't the variable resister help me if needed. If the resistance went up because of this, wouldn't one of those devices simply trim the resistance to bring it back into range?

  5. #5
    Constant Bitrate
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    1. The relay coil resistance has nothing to do with the relay switch contacts. The relay coil is energized with 12volts from whatever switch you're using to turn it on.
    The relay is simply switching the steering wheel wires with none of the 12volts applied to the relay coil going into the steering wheel wires.

    2. Soldering will have a negligible affect on overall circuit resistance.

    3. Resistance in a circuit can not be removed by adding components.

    From your last sentence and the diagram you linked, it's clear that you don't really understand much about electrical circuits. The orange box for the relay gives no clue about how it is switching the wires you have going to it. It should be a diagram more like this..http://binatani.com/lexus-harness-90...ring-diagrams/ (this was just the first pic that came up on google)
    This diagram shows a simple SPST (single pole single throw) relay.

    What car do you have? I don't know everything about steering wheel controls but a friends Volkswagen controls are not a simple resistor network but go through the CAN Bus and required an adapter to connect to the Joycon. My Subaru is a simple 2 wire resistor network. If you have 4 other buttons that all have the same resistance either your measuring something wrong or you don't have a simple resistor network.

  6. #6
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    I made the assumption that all 4pdt circuits were the same and it would be known by the ones who could help, sorry. I hope you were looking at the final post and not the first one.
    http://www.futurlec.com/Relays/GR220PIN4P.shtml (the circuit diagram) that's my circuit layout in the relay.

    The purple switch takes care of activating the relay. 12v will pass through the toggle switch to the relay, and then from the relay will ground. I didn't draw it exactly like that, just wanted to get the gist of what I was trying to do out, my fault for making assumptions in asking for help, I should have laid everything out.
    Infiniti M35x. The resister takes care of the other 4 buttons having the Same resistance, that is not a mistake.

    Ok so the variable resister is for adding resistance then. Thanks.

  7. #7
    Constant Bitrate
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    So your "And then another 4 with the same resistance" doesn't mean those four buttons give the same resistance as each other but rather the two groups of four have the same resistance i.e. 990, 323, 108 and 0 ohms and you're using the 10k to offset the two groups of buttons. I get it now. I'm sorry if I seemed abrupt.
    If you're sure the 10k is what you need you can go with a fixed resistor. I don't know what the resistance range is on the joycon but your highest resistance is just over 1k. If I were doing it I'd replace the 10k fixed with a 5k variable. You'd really only need to add just over 1.5k to the second set of buttons to offset them from the first.

    Having more time to look at your picture it looks like it will work and to your original question I think you will be fine with the resistance to the OE head unit.

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