bicolor led controlled with one output

Discussion in 'General Electronics Chat' started by secuver, Aug 7, 2013.

  1. secuver

    Thread Starter New Member

    Jul 5, 2012
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    I would like to control a bicolor led with the output of an alarmpanel.

    This alarmpanel has an output open collector who can give max. 70mA

    bicolor led green/red

    control voltage of the alarmpanel is 12VDC

    Is their anyone who can give me a simple circuit.
    In one position the led should be green
    When the output is activated the led should be red.

    thanks for the assistance.

    Pieter
     
  2. wayneh

    Expert

    Sep 9, 2010
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    First you need a current-limiting resistor, at least about 470Ω. For testing, I'd start with 1kΩ.

    Do you have any specifications for your LED, such as forward voltage drop (Vf) and maximum current (maybe 25mA)?

    The open collector output is just like a switch ready to connect your LED to ground. I'm not sure how you can control 2 colors with only one switch.
     
  3. secuver

    Thread Starter New Member

    Jul 5, 2012
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    I have a data sheet of the led i want to use
    see the attachment
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    You can use a small relay (SPDT) that is controlled by the output from your alarm. Connect the NC contact to the green LED and the NO contact to the red LED. You can also do it without a relay, but it's more complicated.
     
  5. secuver

    Thread Starter New Member

    Jul 5, 2012
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    when i use a bicolor led i only have 2 connections?
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I am assuming (in a hurry and didn't look at the datasheet) that there are only three leads on the LED: a common and one for the red and one for the green, so the common goes to ground or +V depending upon whether the LED is common anode or common cathode, and then the NC contact goes to the green and the NO contact goes to the red. You will need a relay that has a coil that doesn't draw more current than the alarm output can supply, or else you will need a driver for the relay.

    I am sorry, but I have to leave now; someone here can provide a better explanation.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Yes, per the data sheet, the two colors are antiparallel to each other.
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    OK, then my previous explanation is wrong. Sorry.
     
  9. Ramussons

    Active Member

    May 3, 2013
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    92
    See the attachment.
    You can use any CMOS gate (AND, OR, NAND, NOR, INV, Buff).
    Put a Pull up resistor on your signal output (1 KΩ) and feed this setup.

    You need to find the right orientation of the Bi LED to get the correct colour.

    Ramesh

    Correction: the resistors are 650 Ohms !
     
  10. crutschow

    Expert

    Mar 14, 2008
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    You can use a bridge circuit. That would require four transistors or a DPDT relay. Which would you prefer to use?
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    How I (with my limited skills) would do it.
    Just get a 2 form C relay
     
  12. secuver

    Thread Starter New Member

    Jul 5, 2012
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    Is it not possible to do this with just en circuit of resistors and not with extra components?

    Because i would like to do this for more than one output
    if this works i would like to do this 4 times 16 outputs
     
  13. secuver

    Thread Starter New Member

    Jul 5, 2012
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    so if i see this right you just use a little relay with two contacts en you switch the polarity on the diode?

    wich type of relay should i use to make this circuit?
     
  14. secuver

    Thread Starter New Member

    Jul 5, 2012
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    if i use this circuit and the bicolored led needs 20mA and has a forward voltage of 2V

    if i calculate this right then i would need a resistor of 10V/0.02A = 500Ohm

    can someone confirm this?

    thanks
     
  15. Papabravo

    Expert

    Feb 24, 2006
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    +12V on the VCC pin of an LS part exceeds the maximum rating and WILL let the magic smoke out. Were you thinking of a 4000 series CMOS part?
     
  16. Papabravo

    Expert

    Feb 24, 2006
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    No. I think it is unlikely that there is a circuit consisting of resistors that will produce anything like an acceptable result on a 2-leaded bicolor. Looking at the schematic symbol you have three conditions.
    1. No current flows in either branch -- Off
    2. Current flows left to right -- RED
    3. Current flow right to left -- GREEN
    Resistors are simply not capable of current steering. Where did your expectation that this might be possible with a couple of resistors come from? Was it just a vain hope or do you know something that we don't?
     
  17. secuver

    Thread Starter New Member

    Jul 5, 2012
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    i only need two of the tree conditions. i don't need the off condition

    it my Always be red or green and not off.
     
  18. crutschow

    Expert

    Mar 14, 2008
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    Here's a circuit using a CD4049 Hex driver. Besides the driver, 3 resistors are required. The R1 and R4 values may need some tweaking in the actual circuit to get the desired LED current values.

    I used some arbitrary LED models I had for the simulation.

    Note that power and ground are not shown for the CD4049.

    LED Driver.gif
     
  19. crutschow

    Expert

    Mar 14, 2008
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    Here's an alternate circuit using one transistor and 3 resistors.

    LED Driver.gif
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It only needs 4 resistors, using a variation of Ramusson's circuit (so instead of a CMOS output it is a open collector driver with a pullup resistor.

    The 4 resistor values will need to be carefully chosen to give the right 2 currents through the LED.
     
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