Using a SCR with a bi-color LED

Discussion in 'The Projects Forum' started by Otaku, Dec 22, 2010.

  1. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    Hi all,
    I'm trying to use a common-cathode bi-color LED with a SCR. I need to have the red die lit at all times, and the green die light when the SCR is triggered. Here's a circuit drawing. This configuration keeps the red die lit, but the green die will not light when the SCR is triggered. If the red die is off, I can trigger the SCR to light the green die but if I connect the wire for the red die, the green turns off. At no time can I get both dies to light when the SCR is in the circuit, but I can light both by attaching both LED anodes to V+. All advice is appreciated. Thanks!

    Gary
     
  2. #12

    Expert

    Nov 30, 2010
    16,321
    6,818
    You're making them share the same 220 ohm resistor. Use 2 resistors, one in each anode circuit.
     
    Otaku likes this.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    An SCR is an AC device. When triggered and forward biased on DC, it will latch on.
     
  4. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    That's why I'm using them in this circuit. I'd like the red die to be on 100% of the time, and the green die to latch on if a certain condition is met.
    I'll check out the dual-resistor thing. Thanks!


    Edit - the dual resistors did the job. Thanks again!
     
    Last edited: Dec 22, 2010
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    If you take the SCR out of the circuit, and put the switch directly to the Green LED, does it work? (yellow-orange-ish light when both are on).
     
  6. Otaku

    Thread Starter Active Member

    Nov 19, 2008
    128
    2
    Yes, it does. I could light either red or green with the SCR, and both at the same time. The only thing I couldn't do was to light the green separately with the SCR when the red was on, and vice versa. The dual-resistor suggestion from #12 did the trick - I can now leave the red die lit and switch the green via the SCR so that both are lit at the same time.
     
  7. #12

    Expert

    Nov 30, 2010
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    A "thank you" goes a long way with me. It's good to get them once in a while
     
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