How to determine values for unmarked IR receiver

Discussion in 'General Electronics Chat' started by Cretin, Jul 30, 2013.

  1. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    I found a couple of IR receivers, with just a few generic part #s listed on their backside. Googling them didn't pull up any information, and I don't want to throw them. Two Things

    1: I need to determine which pin isoutput, gnd and Vs

    2: How can I determine the carrier frequency of the IR receiver? I have an idea but will it work?

    I have a function generator and some IR diodes. I will energize the diode by using the function generator, and slowly increase the frequency until i get a response from the IR receiver. I can determine this by setting up the IR receiver in a small circuit with an LED, and when the LED turns on, it means that the IR diode is emitting a signal at the carrier frequency of the IR receiver. I can then record the frequency from the function generator.
     
  2. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    That should work. Note the low and high frequencies that it turns on / off at and pick the middle as the best estimate of the operating frequency.

    Bob
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    You can find the pinout of 3 pin IR receiver modules quite easily.

    First see if you can identify the ground pin, sometimes it's connected to the metal shield or can.

    Then use a regulated +5v DC supply, and connect one pin the gnd and the other two pins through 1k resistors to +5v.

    The power pin will draw more current than the output pin, which is quite high impedance (when there is no IR signal).

    It also helps if your regulated 5v DC supply has a 10mA or 20mA current limit for when you try to use the sensor for the first time (ie when you remove the 1k resistor from the power pin).
     
  4. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    Alright so I put together these circuit, and I am having some issues, hopefully you can help me out.

    1: My LED indicator diode is always on, no matter what I tune the frequency of the function generator to.

    2: I have oriented the VCC and GND in every possible way, and I believe this to be the correct way, after also trying the current test.


    Now, when I connect positive and negative from my battery source into the circuit, the LED turns on immediately, no matter what frequency is being generated through the IR diode.

    NOTE: The top right diode is the infrared, connected directly to the function generator through alligator clips.

    [​IMG]
     
  5. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    Here are some very useful suggestions:

    1: Cover up the circuit with a thick cardboard box to block out the ambient IR light (from the sun and incandescent lights).

    2: Read more about IR diodes and IR sensors. Yes, your IR sensor is selective to the frequency it responds to, but all it does is allow current to flow through it. The IR diode is just like an LED, except for the color of light it generates. LEDs generate light between 700nm (maybe as high as 800nm) and 400nm, (maybe as low as 380nm). IR diodes generate light from 380nm down to about 300nm. There are about 12 different frequencies you can get easily. The IR sensors are made to match the frequencies of the IR diodes.
     
  6. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    IR demodulators need power supply decoupling and often a pull up resistor. A schematic will be in the TSOP1138 data sheet. The AGC might not be happy with a constant carrier signal.
     
  7. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    The IR sensors are made to match the frequencies of the IR diodes.

    Wait a second, so using my frequency generator I can't actually set the IR Diode to pulse at a certain frequency?

     
  8. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    Yes you can. But if the sensor has the best response at 320nm and the IR diode output is highest at 380nm, you will probably not have a response since there is not enough light at 320nm.
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    Pulse frequency yes, but you cannot control the wavelength or frequency of the light it produces. That's why a transmitter and a receiver need to share a wavelength of operation.
     
  10. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    Ah! I see wayneh, so not all IR diodes will work with all receivers
     
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