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Which switch do I need? - just need a bit more info

Discussion in 'General Electronics Discussion' started by jousley, Feb 24, 2013.

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  1. jousley

    jousley

    14
    0
    Jan 14, 2013
    Hey all. my project involves two power wires coming into a single switch. one is 5V and one is 12V. I want a simple rocker switch so that when in the up position, the switch uses the 5V power source and powers circuit A. When the switch is clicked down, it utilizes the 12V power source and powers circuit B.

    I did some research and thought that I needed a DPST switch. I purchased one and it came with 4 pins. No instructions on the wiring. But when I went to test it, I put the 5V power source on one pin, and a 5V LED, and no matter which pin I put the + wire for the led on, it lit up. So 5V power source on one pin, and the 5V LED lit up on every other pin without the switch being switched? I hope this makes sense.

    Am I missing something? Is this the right switch? how should it be wired? I'm a bit confused because I was pretty sure this is the switch that I needed, but am having difficulty understanding the wiring. All knowledge is appreciated.
    Thanks
    J
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    You need a SPDT to make it easy... You should use a 'break before make' switch, this will avoid any potential shorts... It might even pay to use an on-off-on switch vs a on-on switch...
     
  3. jousley

    jousley

    14
    0
    Jan 14, 2013
    thanks... I have a SPDT switch with 3 pins.. its an on-on.. but if I get an on-off-on, can you help me out with teh wiring... cuz the wiring diagrams that I googled, for a SPDT showed one hot coming in - to control 2 circuits.. but I need 2 hots coming in..

    if you could help me out with operational steps i'd apprecaite it.
    J
     
  4. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Mirror the wiring, two hots in one control out...
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    A careful reading of those sentences shows that you need a DPDT switch. These have six terminals, which you need to wire as follows.

    +12V-------------------o . o
    to circuit B <--------o . o---------> to circuit A
    . . . . . . . . . . . . . o . o-----------------+5V

    As CocaCola suggested, you can use an ON-ON switch (two positions) or an ON-OFF-ON switch, aka "centre off", which has three positions. Both have six terminals.

    You can also get these switches with different biasing arrangements - standard switches are stable in all positions, but "biased" switches have "momentary" operation in one or both directions, like a pushbutton; in one or both positions, they will spring back to the centre position if released.

    Because of how they're made internally, rocker switches usually have the "sides swapped round". If you push the switch into the downward position, the contacts that close are the upwards contacts, and vice versa. That's why I've drawn circuit A being switched by the bottom contacts.
     
    Last edited: Feb 24, 2013
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Missed the fact you wanted to power two circuits, thought you just wanted to switch supply voltages, do what Kris suggest... The SPDT will only flip flop from 5 to 12 on a single circuit...
     
  7. jousley

    jousley

    14
    0
    Jan 14, 2013
    thanks so much.. it worked perfectly... and now I'm a bit more knowledeable on DPDT..

    thanks again
    J
     
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