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Reading the intensity of an IR Led using a PNA4601M IR Receiver

Discussion in 'Electronic Basics' started by BurningFuses, Nov 6, 2013.

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  1. BurningFuses

    BurningFuses Guest

    I'm trying to detect if an IR Led is on and if it is how intense is the light.
    For this purpose I tried to use a PNA4601M IR Receiver ( that I bought from Parallax a while ago.
    I thought the I could simply connect the Vcc of the IR Receiver to 5v, the GND and read the voltage out through the Vout. The higher the voltage, the stronger the IR Light shinning on the IR Receiver. But that is not what happened.
    After applying 5V to the Vcc, connecting the GND and reading the output (Vout), I get 5V (a bit lower than the input), even with the IR Led turned off.
    What am I missing here? Any clues?
    Thanks a lot,
  2. Phil Allison

    Phil Allison Guest

    ** A digital camera will do that.

    ** The full name is " modulated IR digital code receiver ".

    BTW: Do you think "steak sauce" is made from steak?

    .... Phil
  3. My favorite way for detecting light is to stick a photodiode across the uA current input leads on my DMM. Bang you're done.. and if you know the wavelength then you have a decent measure of the light intensity. (Assuming access to the photodiode data sheet.)

    George H.
  4. OK.. I guess that's for *really* low light levels! I futzed around to get1uA of photocurrent...(Pretty dark.) On the volt/ milli volt scale this registered as ~200mV...
    (One might worry about the input impedance of the meter on the milli-volt scale... I know some go into a high Zin mode.)

    So the diode had an resistance of ~200k ohm... Hmm why not 25mV/1uA = 25kohm?
    (I seem to be confusing myself.) Yeah, I know, with light shinning on it the I-V curve is displaced downwards.

    I tried a smaller area PD.. more light for 1uA.. and now that gives 230mV in voltage mode.
    (scratch scratch...time for lunch.)

    George H.
  5. OK this is nice.. here’s the forward voltage drop vs bias current.
    Vf is for the PD I used yesterday ~200mV at 1 uA. The PIN-44 is one we commonly use...about the same area (for comparison.) There’s something like100 ohms of resistance in series with the diode drop... but it’s non-linear. (less resistance at 10mA)

    For these PD’s you’ve got to be below ~100mV to not have any current sucked up by the diode. But for low light levels you could just use the logarithmic behavior of V to get an estimate of the light intensity. (You’d have to do the I-V of ‘your’ PD first.)

    George H.
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