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Help wiring a DPDT switch

Discussion in 'General Electronics Discussion' started by Apostrophe, Jul 19, 2021.

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  1. Apostrophe

    Apostrophe

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    Jul 19, 2021
    Hello, I'm new to the forum. I'm trying to wire a DPDT switch in the following configuration: ON - OFF - ON (both). What I mean by that is in the 2nd ON position, I want both circuits active. I've attached a simplified image which depicts what I mean. Is this possible to do with a DPDT switch, or will I need a different type of switch? I've tried a few things now, using LEDs as a placeholder for the actual components, but I always end up with both LEDs on in both ON positions. Thank you for your help.
     

    Attached Files:

  2. DBingaman

    DBingaman

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    Jun 27, 2021
    What you have in your diagram is a single pole double throw with a 'center off' position. Is that the switch you want to use? If so here is one way to make it happen (assuming your load is DC):
    OnOffOnOnPNG.PNG
    The diode is reverse biased o the left and only the right light turns on. The middle position both off. Last position diode is forward biased and both lights will be on.

    A DPDT switch 'Double Pole Double Throw. It has two poles and two positions, thus it's name. If that is confusing take a look here:

    http://www.learningaboutelectronics.com/Articles/Double-pole-double-throw-switch-DPDT
     
    Last edited: Jul 19, 2021
    bertus likes this.
  3. Apostrophe

    Apostrophe

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    Jul 19, 2021
    I do have a Double Pole Double Throw switch, the diagram is just a profile drawing so you can't see the other leads in the image. I should have used a different image perhaps to make that more clear. The switches I have feature 6 metal leads and are indeed DPDT. I would prefer not to add in an additional component (the diode you mention) if possible, as I would like to keep this as simple as I can. I'm a mechanical engineer, not an electrical engineer; and as you may have noticed, my electronics knowledge is very lacking. I've never used such a diode before and I don't know what you mean by forward/reverse biased. With a DPDT switch can this be accomplished without any additional components? Thank you for your response.
     
  4. DBingaman

    DBingaman

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    Jun 27, 2021
    Ok, it looks like you have a DPDT switch with an additional 'off' center position. Let me draw up something for you, give me a minute or two...
     
  5. DBingaman

    DBingaman

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    Jun 27, 2021
    This should do what you want:
    OnOffOnOn2.PNG
     
    Apostrophe likes this.
  6. Apostrophe

    Apostrophe

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    Jul 19, 2021
    Thank you for the reply, I will try that out and report back.
     
  7. DBingaman

    DBingaman

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    Jun 27, 2021
    Updated the diagram to make it clearer. Labeled each node on the switch and showed bottom of switch: OnOffOnOn2.PNG
     
    Apostrophe likes this.
  8. DBingaman

    DBingaman

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    Jun 27, 2021
    You are welcome. Being you are an ME I updated the circuit to make it clear by numbering all the switch contacts and providing an underside of the switch so you can correspond each switch terminal to points in the circuit.
     
  9. Apostrophe

    Apostrophe

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    Jul 19, 2021
    I'm still not getting it... I either end up with only Lamp 1 ON and only Lamp 2 ON (for the two ON switch positions), or only Lamp 2 ON in either switch position and Lamp 1 staying OFF always. I am horrible at reading circuit diagrams, even with your helpful revision... The wiring appears to me to be as you've indicated, but I must be making a silly mistake somewhere.
     
  10. DBingaman

    DBingaman

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    Jun 27, 2021
    Can you provide a part number for the switch? That will allow me to verify both you and I are actually dealing with a switch that operates that way I think it does.
    Don't sweat it, we will figure it out.
     
  11. Apostrophe

    Apostrophe

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    Jul 19, 2021
    I've almost got it to work, but I'm seeing something I can't explain. In the 1st ON position both Lamps are on, and in the 2nd ON position only Lamp 1 is on, which is exactly what I want... However, when switching between the 2nd ON position to the center OFF position, Lamp 2 flashes on for a fraction of a second before going off. Do you know what could be causing this?
     
  12. Apostrophe

    Apostrophe

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    Jul 19, 2021
  13. DBingaman

    DBingaman

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    Jun 27, 2021
  14. Apostrophe

    Apostrophe

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    Jul 19, 2021
    I believe it should be the GRS-4023A, as I ordered these directly from the link I provided, and that is what is indicated on the Digi-Key page I linked. However, I see no indication on the switches themselves that would verify this, and to be honest I have no idea what the difference is between those three models, what could those parenthesis around the word 'on' mean?
     
  15. DBingaman

    DBingaman

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    Jun 27, 2021
    Ok, I think I understand the switch terminology. When in parenthesis you have to hold the switch in that position or it springs back to off. So I think you have the 'A' version. That is you can switch it to any of the three positions and it stays in that position?
     
  16. Apostrophe

    Apostrophe

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    Jul 19, 2021
    correct, it stays in whatever position it is set to without springing back.
     
  17. DBingaman

    DBingaman

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    Jun 27, 2021
    I had
    I had to look that up on the internet. I did not know what the parenthesis meant either. What it means is you can push the switch into that position but it will return to the off position when you release it. (Momentary On). So yea, you have the A version.
     
    Apostrophe likes this.
  18. DBingaman

    DBingaman

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    Jun 27, 2021
    Concerning the one LED flashing on. It think that has to do with 'break' before 'make'. There are two types of switches on the market. One is called 'make before break' and the other 'break before make'. If we have a 'make before break' it would explain the one LED turning on momentarily when going back to the off position. How critical is it that this not occur in your application?
     
  19. Apostrophe

    Apostrophe

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    Jul 19, 2021
    This is not a personal project, I'm designing a product which my company intends to sell as a high-end lab instrument. (Yes, I realize that I am not prepared to be handling this... I'm a brand-new ME graduate and they are trusting me to be the lead designer on a difficult project relative to my level of experience. I'm confident with the mechanical aspects but I'm currently pretty lost as far as the electronics are concerned, as you can see even the power switch is giving me trouble once they decided to add a 2nd function). So in short, I'm going to assume that it will not be acceptable for one of the components to flash on for a moment when the device is powered off.
     
  20. DBingaman

    DBingaman

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    Jun 27, 2021
    It sounds like the rocker switch is for a moment going 'to far' to the next position before ending up back in the center position.
     
    Apostrophe likes this.
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