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Some basic help please

Discussion in 'Electronic Basics' started by Kamus of Kadizhar, Dec 7, 2004.

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  1. I've build a couple of the IR receivers shown here
    http://www.lirc.org/receivers.html but now I'd like to get a little
    fancier.

    Mostly, I'd like to add 2 LEDs, one that turns on when the serial port is
    activated, and the other when the receiver gets a signal.

    I located some 5V LEDs (they have an internal resistor, pretty neat) and
    tried to add them in a way that makes sense to me.

    Since the voltage regulator provides a nice steady 5V, I connected one LED
    across pins 2 and 1 of the TSOP. That works fine; the LED comes on when
    the circuit is energized.

    The signal received LED is a bit more problematic; the TSOP holds pin 3
    high when inactive, and drops pin 3 to ground when a signal is received,
    an LED across pins 2 and 3 should work. But when I try that, I get a
    latching effect - once the LED comes on, sometimes it latches and stays
    on. The circuit won't receive any more signals either. I thought perhaps
    the LED, being so close, might be sending enough IR out to mess with the
    receiver, but adding shielding did not help.

    I thought this might be some excessive current drain, so I disconnected
    the LED between pins 1 and 2, but the latching effect stayed.

    I played around with it a bit, but then decided I did not know enough
    about this sort of stuff.

    So, any suggestions for modifying the circuit to add a power on and signal
    LED?

    FWIW, the 5V LEDs are Chicago Miniature part no. 4302Hn-5V or 12V, and
    they come in different colors (the n is the color code, 1 for red, 5 for
    green.)

    TIA,

    Yan
     
  2. Guest

    Can you still measure 5V across the regulator output when it's in the
    latched state?

    This guy http://www.electronics-lab.com/projects/pc/019/ went to the
    elaborate length of having a seperate battery for the activity LED.

    You might be able to get more power by using both RTS and DTR if both
    are asserted.
     
  3. I didn't measure that. I'll put together another one to test on a less
    valuable machine (just in case I fry the serial port....) :)
    That just seems too clunky for my taste.... I wonder why he didn't power
    it off DTR with a voltage regulator? How much current can a serial port
    supply, anyway? I guess I could also go to the trouble of pulling 5VDC
    off a USB port, which may be the way to go - eliminate the voltage
    regulator altogether.

    --Yan
     
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