Change onboard LEDs to optocouplers?

Discussion in 'The Projects Forum' started by Roxy2, Jul 4, 2012.

  1. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    I have just build a Velleman dice circuit (see attached). I would like to use this circuit to run some very large dice for a charity event. So therefore need big lamps. I have decided to use these - http://www.ebay.co.uk/itm/290732266...X:IT&_trksid=p3984.m1423.l2649#ht_3483wt_1180
    As an experiment I have removed 1 led from the circuit board and fitted a 4N25 Optocoupler as I had one lying around. I then attached a 12volt supply through the emitter/collector and then onto a similar LED bulb as above. The flashing of this 12volt LED is fine and it doesn't seem to effect the circuit, however when it is supposed to be off for example when the dice rolls 1 it still has a very small glow.

    Is this optocoupler wholly suitable or should I opt for a MOC3021 or similar? Is there anything else that perhaps needs changing such as the resistor ratings?

    Hope this all makes sense.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Why do you think you need an optocoupler? :confused:
     
    Last edited: Jul 7, 2012
  3. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    The circuit is designed to run a max of 7 3mm red LEDs which I'm guessing run at 1.5volt ish. I need the circuit to run 7 12volt led bulbs (see the link in the original post). The coupler will operate at 1.5 volt as per the original led (effectively that's what it is) and will then complete an internal circuit switching the higher voltage circuit.
    I don't see another way of the original circuit having the power to run larger lamps. Maybe it's me that's confused.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Could find no attachment, E-bay ref is dead. If LED is dim when off there is leakage current-- need schematic.
     
  5. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Ill try again. ebay ref was working when I posted but as you say isn't. Rather than put the ebay ref I have attached the photos of the ebay LEDs.

    3 attachments - 2 of the bulb i would like to use and 1 of the Velleman circuit. At the moment I am using a 4N25 optocoupler. This is in place of 1 of the original LEDs. It then has a 12v supply to it which then goes off to a led similar to the one on ebay. Hope this helps. Ill draw the additional circuit and post shortly.

    The last image shows what I have done (in a rough way).
     
    Last edited: Jul 5, 2012
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Now we see why opto-couplers are required. There may be a slight mis match between origional LEDs & opto LED. 'believe a seperate LED driver [ FET or bi polar transistor ] would be usefull as new LED may require up to 600mA??
     
  7. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Ok. So any more specific recommendations?
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Might try this: Resistor value not critical, need at least 10V on gate.
     
  9. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Thanks for that. I'll give it a go and let you know what happens.
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
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    I have tested optocoupler yesterday while it was built on PCB, soldered battery holder wires to it with NiMH rechargeable 1x.

    The transistor went from High-Z to 0.09V (continuity tester from DMM).

    I believe some LED emitters inside them are infrared wavelength.
     
  11. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    You've lost me now........
     
  12. takao21203

    Distinguished Member

    Apr 28, 2012
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    just saying they don't always neccessarily need 1.8V
    But might not be important for your circuit.
     
    Roxy2 likes this.
  13. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Ok Ill try Bernards idea, and with and without the resistor, and see what happens.
     
  14. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Ok, Ive tried Bernards circuit without the 47R resistor. All looks good. I shall now buy up what I need to complete 2 full sets.
     
  15. Roxy2

    Thread Starter New Member

    Jul 4, 2012
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    Ive tried this circuit, without the 47R resistor and it seems to be ok. I have ordered up the components to make up a full set now and will report back once done.

    http://forum.allaboutcircuits.com/attachment.phpattachmentid=44178&d=1341527812

    Well Ive finally got around to building the first dice. Its still fairly much prototype but it works. I would put a video up but dont know how.

    Its the circuit that is shown in post number 8 without the 47R resistor before the IC.
     
    Last edited: Jul 5, 2014
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