Power IR LED

Discussion in 'The Projects Forum' started by JMR711, Jun 11, 2013.

  1. JMR711

    Thread Starter New Member

    May 8, 2013
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    Hi all! First post.

    I have done some searching on the forums and I didn't find an answer that helped me too much. I have an IR LED and a 9V alkaline battery. The way I am testing how "on" the IR LED is, is by looking at it thru an old camera. I have tested the camera on a TV remote and there is a bright blueish light when I press a button. When I wire up the IR LED with the 9V battery and a 100Ω resistor, the IR LED barely lights up.

    My question is: can a 9V alkaline battery push enough current to power the IR LED? Should I buy a 12V battery with a higher A/hr rating?

    Thank you guys for the help.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,154
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    If you have a voltmeter, take a look at the voltage drop across the 100Ω resistor. That'll tell you the current. If you don't have a meter, get one. ;)
     
  3. JMR711

    Thread Starter New Member

    May 8, 2013
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    I put in a 150Ω resistor and measured the voltage. The batt is 9.6V, the voltage across the resistor is 7.8V. The current then is 52mA. Should be enough but its not lighting up near bright enough. That means Vdrop is 1.8V, that seems a little high for an IR LED.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    The wavelength may be different than what you've used before, so that it doesn't show up as well with the camera trick or it may just be an old and inefficient model. Do you have any data on the LED?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Did you measure the battery voltage under load? It'll be much lower than unloaded.
     
  6. JMR711

    Thread Starter New Member

    May 8, 2013
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    The wavelength is supposed to be 950nm. The batt volt under load is 9.4V. I see the light dimly lit up in the camera. I completely covered the light and camera. The camera was completely blacked out and the light barely turned on.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,154
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    Hmmm, well that rules out the simple stuff. I guess I'd speculate that it's not the greatest LED. There are IR LEDs in the 850nm range that would appear much brighter to a camera. Maybe your other experience was with one of those.

    And I suppose an LED with a less focused beam could be just as bright overall but wouldn't appear so to the camera, since relatively less of the light output is focused into the camera's lens.

    Just some idle speculation. It's tough to diagnose stuff you can't see.

    You might want to take a look at this site. It's a little hard to find stuff but there sure is a lot of info there.
     
    Last edited: Jun 11, 2013
  8. JMR711

    Thread Starter New Member

    May 8, 2013
    4
    0
    Well the end goal of this project is a simple motion sensor. I am going to use a phototransistor to sense the changes. Even tho I cant see the light on camera, can I trust it is still on enough for a significant change in the phototransistor current?
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Probably. Only one way to find out.
     
  10. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    What batteries are in the remote control ?
     
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