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Jittery LED

LSBLSB Posts: 175
edited 2006-05-11 02:11 in Robotics
I'm having what I beleive is a problem with noise. I have hooked the IR receiver (Stock#: 350-00014) up as input to P10. P9 outputs to drive an LED (visible). The leads are short--all mounted on a BOE-BOT breadboard, but the LED flickers randomly all the time as if noise was affecting it. My TV remote makes the LED flicker as expected (indicating, I hope, that it's wired correctly), but even with the IR receiver covered, the LED flashes randomly. Can someone recommend a solution? Perhaps some filtering or something? My BOE-board is old (at least a couple of years) and I doubt my constant plugging and unplugging has done it much good, but even switching holes doesn't affect the average rate of apparent noise. I tried a simple flashing subroutine in hopes of detecting any kind of loose connection--works as exspected, then begins the random flash.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-05-09 03:51
    It could be fluorescent lighting or even random reflections from the IR LED reflecting off something...Have you checked those two sources?

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  • LSBLSB Posts: 175
    edited 2006-05-09 12:40
    No fluorescent tubes in the shop and no IR LED for output--just my TV remote. I should have been more clear--not IR noise, electrical noise from the motor driver though I disconnected my high volt source and motors, the chip is still active. I have caps sprinkled around, but am wondering how to specifically filter the IR signal or how better to filter the driver. Any standard guidlines or tut's to verify my values/placements? It's tight on the breadboard, but I've done my best keeping signal from power...
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-05-09 12:49
    LSB -

    A copy of your PBASIC program would be real handy for helping to diagnose this problem. My suspicion is that you may be using SLEEP or NAP in your program, and if you are, therein lies your problem.

    Regards,

    Bruce Bates

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  • Tom WalkerTom Walker Posts: 509
    edited 2006-05-09 13:09
    The way you have your detector wired in could also cause something like this. If the detector cannot "assert" one state or the other (i.e. is designed to use a "driven" line), then your detector line might be floating...therefore registering an indeterminate state and being an antenna...

    Just a thought...more details needed...

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  • LSBLSB Posts: 175
    edited 2006-05-09 22:07
    Yes, yes! I'm sure this is it. As I read more on microcontrollers in general I think a pull-up or pull-down is required to hoild state between inputs. Only thing that makes sense. I've hacked the program to bare bones--a simple loop that outputs to LED on low (active reception from receiver) and resets on high-- and still get flicker. Hook up is from the robotics with BOE-bot text.

    Also, tried a different sensor--I noticed the one I was using was very hot. Problem much redueced, but the LED will occassionally change states-- normal? or would pull-up/ down improve performance to perfection?
  • SSteveSSteve Posts: 808
    edited 2006-05-10 17:30
    The IR Detector that comes with the Boe-Bot doesn't need a pull-up or pull-down. It does that internally.

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  • LSBLSB Posts: 175
    edited 2006-05-11 02:11
    Then I will persue some "Pseudo fuzzy logic" as described in an article I read recently, thank all of you for your help, and continue with my project in the hopes of contributing something to the completed projects section soon.

    Thanks again,
    Mark
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