Replacing LEDs with Optical switches, how?

Discussion in 'The Projects Forum' started by quant, Oct 24, 2009.

  1. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    In dealing with a Matrice of switches, the best that comes to mind is the present readily available LED Matrice circuits, if only one could replace the LEDs with some type of Optical Switch or for that matter any switch! Then one could easily benefit from their existing software etc.

    Please advise if this is possible at all and if yes how?

    thanks in advance
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Do you have the schematic of the current situation?
    Then we can have a look how to adapt it if possible.

    Greetings,
    Bertus
     
  3. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0

    Would this be a reasonable example(basically any LED circuit would do)?
    thanks

    http://www.bowdenshobbycircuits.info/60sec.gif

    p.s.
    there's also this one.
    60 Light Sequencer using a Matrix

    The circuit below illustrates using a 10x10 matrix to sequence up to 100 LEDs with just three ICs and 20 transistors.

    http://www.bowdenshobbycircuits.info/page5.htm#60sec.gif

    Although the above says sequencer, Vs. my need to turn LEDs/Switches OFF/ON based on any predetermined pattern.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You can put the leds of an optocoupler in series with the origenal led.
    The voltage drop will rise about 1.2 volts by doing this
    (the IR led has a voltage drop of about 1.2 Volts).

    Greetings,
    Bertus
     
  5. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Bertus,
    Thank you so much, that makes a lot of sense. Now I have the following 2 questions:
    1- Can't the LEDs be replaced with the optocouplerto accommodate the voltage drop?
    2- Since the LEDs are turned on and off by a series of pulses(or frequency change or what not, since I do not know how they work), would these short pulses cause any problems in the optocouple? Like they would be turning on and off with every pulse?

    please excuse my lack of knowledge of electronics.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The leds can be replaced by the leds from the optocouplers.
    You will have to limit the current by placing a resistor in series with the leds.
    The maximum current can be found in the datasheet of the corresponding optocoupler.

    Greetings,
    Bertus
     
  7. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Thank you Bertus,
    This seems just great, after all an optocoupler is indeed an LED itself! Now to my other question and sorry for being so lame in this subject.
    I was told the LED is turned ON/OFF like 24 times/second? How would that effect the optocoupler? Would it activate the optocoupler switch 24 times/second too?

    grateful for all your help

    Cy
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Yes, if the led is switched 24 times a second, the transistor in the optocoupler will switch also 24 times a second.
    Speed is of no consern here as there are optocouplers that can switch even in the kHz range.

    Greetings,
    Bertus
     
  9. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Bertus,

    Thanks for the help. I'll go and try this out and keep the forum posted on the progress.

    Best wishes

    Cy
     
  10. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Please check out this simple LED circuit and advice on how to replace the LEDs with Optocouplers.
    The Optocouplers will be used to activate solenoids that are fed off of a 24v supply.

    thanks
    [​IMG]
     
    Last edited: Oct 27, 2009
  11. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Is the circuit shown above Charlieplexing or Multiplexing or neither?
     
  12. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The circuit shown uses multiplexing.
    The row must me low and a colum high to let the led burn.

    Greetings,
    Bertus
     
  13. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Thanks again Bertus,
    Can I just go ahead and replace the LEDs with Optocouplers? Or do I also need to add resistors, diodes etc.?

    Is multiplexing preferred to Charlieplexing?

    appreciate your help.
     
  14. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    There are already 330 Ohms resistors in the schematic.
    This value is dependend on the led characteristics of the optocoupler.
    There is also a limatation at the controller side.
    I do not know how much current an out put of the controller may deliver.

    Greetings,
    Bertus
     
  15. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
    Hi Bertus,
    Thanks for the quick reply.
    I'm going to try with PC817 and/OR P521. I'll just do some trial error and hopefully get it right.

    cheers
     
  16. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
  17. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
  18. quant

    Thread Starter Active Member

    May 21, 2009
    114
    0
Loading...