Illuminated Switches problem to solve

Discussion in 'The Projects Forum' started by hardcj, Apr 14, 2010.

  1. hardcj

    Thread Starter New Member

    Apr 14, 2010
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    0
    Firstly hello!

    I'm currently building a panel with 16 LED illuminated switches. The LED's are 12v 25ma and the switches are Push to Make. Im using the switches to select between 16 programs on a lighting controller.

    My problem is, I need a circuit that will allow the LED of the selected button to illuminate. But it needs to be cancelled out once another program is selected so only 1 LED is ever illuminated? It's been about 4 years since I did A-Level electronics and i have a few ideas using X-OR gates or by using some form of multiplexer/demultiplexer combination?

    Can anyone help and has anyone else designed this circuit?

    Many Thanks

    Craig
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    Post ur circuit first mate. I don't think any one has built such a thing here yet
    we can go on from there.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    We do need some additional information. If the switches are momentary, what are the functions? Are the selections to be maintained after the individual switch is pressed? If so, how is the selected function to be canceled? What kind of signal is to be produced, and how does it get used?
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Something like a diode matrix to produce a four bit code representing the one-of-sixteen active mode. An extra diode from each button to give an any-button gate or clock signal, enabling a four bit latch to 'grab' the code.

    Feed that to a four-to-sixteen line decoder chip and you have sixteen individual mode select signals, which can also be used to drive the LEDs in the appropriate buttons.
     
  5. hardcj

    Thread Starter New Member

    Apr 14, 2010
    3
    0
    The lighting controller only needs a momentary contact so I dont have latching switches. And the selection for the programs in the lighting controller are all sorted.

    But I need a seperate circuit for the LED part of the illuminated switch which will need to keep the LED illuminated and needs to self cancel itself out when another button is pressed. So it will be a completely stand alone system.

    The illuminated swiches I'm using are: http://www.ikonavs.com/Wall16.html
     
  6. hardcj

    Thread Starter New Member

    Apr 14, 2010
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    Hi,

    Thank you for your advice! Would you have a diagram at all for the diode matrix? I cant find one anywhere and thats how I was going to do it with a decoder/demultiplexer.....but i couldnt figure out the input control or find anything for it!

    Many thanks
     
  7. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
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    For the diodes, allocate each switch a number from 0 to 15.
    Write the numbers in binary, so 0000 0001 0010 0011 0100 0101...

    Connect diodes from each switch to the four outputs, so diodes connect where you need a '1' for that switch, with anode to switch and cathode to output. That's assuming the common of all switches is positive power. Add pull-down resistors at the four matrix outputs so lines without diodes stay at logic 0.

    If the switch commons are grounded, fit the diodes the other way around and in the Zero positions rather than the One positions, then use pullup resistors to V+.

    You also need an extra single diode from each switch to a common point (with a pullup or pulldown) to give an 'any switch pressed' signal to store the new selection number.
     
  8. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    Can you tell us if the lighting controller uses an active low or an active high "switch press" signal and the voltage levels involved (5v, 12v)?
     
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