Connect with us

IR Receiver Problem

Discussion in 'LEDs and Optoelectronics' started by Flashfreeze, Aug 20, 2018.

Scroll to continue with content
  1. Flashfreeze

    Flashfreeze

    3
    0
    Aug 20, 2018
    Hi, I'm very new to electronics so any advice on my current observation is very much appreciated.

    I'm wiring a TSOP34838 to a raspberry pi to try and send some signals to execute a program with Lirc. The wiring is pretty simple, 3.3 input, ground to ground, and receiver output to GPIO pin 7. Wiring is directly from receiver pins to the gpio.

    I saw that Lirc did not register any input at all. So I measured the voltage drop when a remote is pressed and found that the voltage of the output pin did not drop to 0v when the remote is pressed; but only by 10% (3.3v down to 2.9v). I've tested 4 other receivers and they produce similar results.

    My understanding is that receivers will drop the voltage down to 0 when it receives a signal, allowing the gpio to sense an input. Is there a fundamental mechanism I'm missing here?
     
  2. Audioguru

    Audioguru

    2,689
    608
    Sep 24, 2016
    The TSOP IR receivers do nothing if the IR is not modulated at their set frequency (yours is 38kHz) and with certain burst durations (yours is 40 cycles of 38KHz to 75 cycles of 38kHz and similar pause times between bursts). If your burst lengths are longer then nothing happens to avoid triggering by compact fluorescent light bulbs operating at 38kHz.
    The maximum allowed output current is 5mA and it works well when the output current is only 0.5mA.

    It is all explained in the datasheet.
     
  3. BobK

    BobK

    7,671
    1,681
    Jan 5, 2010
    Are you just measuring the output with a multimeter? The output is a series of pulses, not a steady signal. You need a scope or logic analyzer to look at it.

    Bob
     
  4. Audioguru

    Audioguru

    2,689
    608
    Sep 24, 2016
    As I said, the datasheet shows that the durations of bursts and pauses between bursts of output pulses must be as listed on the datasheet. Maybe your remote makes different bursts and pauses durations then the IR detector ignores them. If your remote produces continuous IR or a frequency that is not 38kHz then it also will ignore them.
     
  5. Flashfreeze

    Flashfreeze

    3
    0
    Aug 20, 2018
    Thanks for the replies. Yes, I only have a multimeter, don't have access to a oscilloscope at the moment.
    The thing is, the original remote and receiver was bought as a pair, so I assumed it should work. I bought the extra receivers for other projects.

    I'll have a look at the current. But as you said, it's probably a remote issue.
     
  6. Audioguru

    Audioguru

    2,689
    608
    Sep 24, 2016
    The output of the receiver is pulses that you multimeter cannot properly measure.
    Since the tx and rx do not work then are they a cheap Chinese product from ebay?
     
  7. BobK

    BobK

    7,671
    1,681
    Jan 5, 2010
    What signal are you expecting to see on the receiver when you push a button on the remote?

    Bob
     
  8. Flashfreeze

    Flashfreeze

    3
    0
    Aug 20, 2018
    It turns out the problem is me not RTFM... I misconfigured parameters, pins, using physical pins instead of BCM pins.

    Sorry for the trouble and thanks Audioguru and BobK for the help.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-