Connect with us

Dummy needs help!

Discussion in 'Electronic Design' started by [email protected], May 27, 2007.

Scroll to continue with content
  1. Guest

    Dummy needs Help!

    I am trying to connect two LED 12 vdc lights to come on at intervals
    on a 3 position rotary switch. . . Position 1 = Off. . . Position 2
    = One light comes on. . . Position 3 = Both lights come on. . .
    This doesn't seem too hard except that in Position 2, where only one
    of the two lights are suppose to light, the power back feeds to the
    second light through the wiring connected to Position 3 "where both
    lights are wired together." I have considered using a diode to block
    the travel of the (12 vdc) voltage in one direction, but I don't know
    what size diode to get or if size even matters since I am only using 4
    to 8 LED 12vdc lights here. I have also considered using a very
    small 12 vdc relay here, but that seems like a lot of unnecessary work
    and consumes a little more power and space than I want. Does anybody
    have any ideas that will help?? Thanks. . .
  2. Jamie

    Jamie Guest

    LED's draw very little.
    I assume you are using LED's designed for 12V with a resistor already
    inside of them ? If not I suggest you do.

    You can use a 1N4000 series type that is good for .5 amps or more as
    the back feed block.
  3. Rich Grise

    Rich Grise Guest

    Two - one per each LED.

  4. ehsjr

    ehsjr Guest

    This will do it for you:

    +12 ---Vin|LM317|Vout---+
    ----- |
    Adj [62R]
    | |
    | | |
    o1 | |
    SW o2----------+ |
    Gnd ----------------o-->o3----------------------+

    The LM317 and 62 ohm resistor fix the current at ~20 mA.
    For a different current, the resistor value must be changed.
    The switch determines if the current goes through just the
    resistor, or the resistor and the first LED, or the resistor
    and both LEDs.

    There is no such thing as a "12 volt LED" per se, but there
    can be an LED/resitor combination that's rated at 12 volts.
    The circuit above requires LEDs without resistors. If you
    must use 12 volt LED assemblies (LED + resistor), use diodes,
    as others have said:


    | |
    SW D2 | |
    +12 ----------------o-->o3--->|---+ |
    | |
    | D3 |
    Gnd ----------------------------------------------+

    The above uses 3 diodes so that LED1 will get the
    same voltage in position 2 as it gets in position 3,
    and so that LED2 gets the same voltage as LED1. You
    could probably use a jumper in place of D1 and D3 and
    not see any difference.

  5. Jasen

    Jasen Guest

    Put a diode between 2 and 3 instead of the piece of wire you are using.
    Or use a 2 pole switch.

    1 2 3 C

    0 0 0 0--- lamp2 --.
    | |
    0 0--0 0--- lamp1 --+-- 0V

  6. Jasen

    Jasen Guest

    12V -----[470R]-------------[LED]---+---[LED]---+
    | |
    o1 | |
    SW o2--[81R]---+ |
    Gnd ----------------o-->o3----------------------+

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day