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4N35+Capacitor+LED for PC Case

Discussion in 'LEDs and Optoelectronics' started by Marvinmycat, Feb 25, 2013.

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  1. Marvinmycat

    Marvinmycat

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    Feb 25, 2013
    Hello Everyone,

    First off, I’m a total n00b at this. 30 years ago I was on top of anything electronics, but I haven’t had much experience since then and since I haven’t used it in that long, I’ve completely forgotten everything I’ve learned.

    What I’m trying to accomplish is a simple setup in my PC case. I’d like to run an LED that glows brighter and dimmer according to my hard drive’s activity light. I’d like to run everything off of a +5V Molex. In order to do this, I understand that I will need a 4N35 or 4N25, a capacitor, and LED, and possibly a resistor.

    The 4N35 would receive the HDD signal via the motherboard via a 5V signal. The 4N35 would then in turn charge a capacitor that supplies the LED.

    I also want to be able to switch between the PC case’s HDD indicator LED and the extra LED, not running both, but one or the other via a lighted ON/ON or ON/OFF/ON DPDT switch.

    The problem I’m having is that I do not know enough about Optoisolators/Couplers to make an educated guess as to which one I would need. Everything on this circuit would be run from the +5V Molex, except for the HDD signal, but that too is also +5V.

    I also don’t understand that any capacitor/LED combination schematic that was able to find, puts the capacitor on the 4N35’s Base pin.

    So my questions are:

    • Which Optoisolator/Coupler would I need (there are a few types that forward some sort of signal or another, I just want to open and close a +5V current)?

    • Does the capacitor really go on the Base pin 4N35?

    • Since the Molex is rated [email protected] what would a recommended resistor be for this, using an LED with the following specs - Typical voltage: 5.0, with a maximum voltage of 6.0V, 30mA (max)?

    • Is the attached schematic even close to accomplishing what I want to do?

    • Why can’t I leave well enough alone?

    Thank you in advanced for any help you can provide me!
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,838
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    Sep 5, 2009
    Hi there
    welcome to the Electronics Point forums :)

    OK firstly, that wont work ... opto couplers dont supply any power, they are basically a semiconductor switch. So you will need a 5V supply to go via a current limiting resistor to the LED to the collector of the optocoupler then the emitter of the opto coupler will go back to the same 0V rail as the 5V supply. The capacitor is not needed

    the switching between the 2 LEDs isnt too difficult
    any opto will do, the 2 you have mentioned earlier are quite OK

    I really dont see the practical use for this. but anyway....

    forget the capacitor ... as said earlier it wont be used

    The base of the transistor in the opto may or may not be accessible from a pin of the opto
    anyway it wont be used. Its the light from the LED INSIDE the opto the turns the transistor on and off NOT anything connected to the base

    The ratings of the molex connector, in this case , are irrelevent, as the LED you will be driving only needs ~ 20 - 25mA

    cheers
    Dave
     
    Last edited: Feb 25, 2013
  3. Marvinmycat

    Marvinmycat

    2
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    Feb 25, 2013
    Thanks for getting back to me so quickly, davenn.

    I think I was thrown by product titles such as "Optocoupler Output Type:phototransistor" & "with Base DC-OUT." Also, the voltage rating were throwing me, but I guess that is te amount of current that they can handle being passed through them? Basically this type of unit is just a switch using a tiny photocell to switch on and off a circuit. I was over thinking it, I suppose.

    The reason for the capacitor is so that when the LED light switches on and off, it doesn't have that strobe effect and launch me into some sort of epileptic fit. I want to have the LED glow and fade slowly as it receives the HDD signal, whereby I thought that the capacitor rated around 22-33 microfarads would accomplish this.

    I was also thinking of running another Power LED for the system (in the attached schematic).

    The reason for this whole thing is that I'm quite anal when it comes to monitoring my computer builds when they run. I want to do something a little fun with this next build and seeing as how my cases always end up in my desk, I can't see the HDD activity light during normal use. I have two Crystal Skull Vodka bottles on my computer desk and though it would look cool to have them act as my Power and HDD Activity lights. I just didn't want to have the HDD LED flashing on and off when turned on, as that would be quite annoying, instead having it glow to life when there is HDD activity, then slowly fade out when the disk spins down.
     

    Attached Files:

    Last edited: Feb 26, 2013
  4. EinarA

    EinarA

    28
    0
    Feb 11, 2013
    This might have a chance of working if you put R1 in the emitter circuit; between pin 4 and ground. Supposedly the photodiode , part of the collector, will charge up the cap and the LED current will follow suit. Don't have an optocup to try it out. As shown a cap won't do much, but try both ways.
     
  5. davenn

    davenn Moderator

    13,838
    1,952
    Sep 5, 2009
    no its not and no it wont

    Dave
     
  6. davenn

    davenn Moderator

    13,838
    1,952
    Sep 5, 2009
    the voltage rating often ~ 1000V is the breakdown voltage across the gap between the photo diode and the transistor, nothing to do with the current rating of the diode which is usually ~ 20-30 mA

    I really dont see the cap off the base doing anything .... maybe Steve or Kris may elaborate

    ok :)

    Dave
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    I think it's going to reduce the bandwidth of the device significantly (like a low pass filter)

    This provides a lot of information about what the base connection can be used for.
     
  8. EinarA

    EinarA

    28
    0
    Feb 11, 2013
    I looked at steve's link and it tends to back up what I said in my first post. I think I'm getting fed up with no nothings attacking my good and/ or reasonable ideas.
     
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