interference

Discussion in 'Embedded Systems and Microcontrollers' started by fisho, Dec 1, 2010.

  1. fisho

    Thread Starter Member

    Nov 4, 2008
    18
    0
    Hi there

    I recently built a Pic16f84a controller for laundry machine.but every time a contactor makes and breakes the micro resets. tried a pi filter at the mains input but it didn't help.a simple glitch resets the micro. pls help. regarding the snubber diodes u asked there are the fools diode across each relay coil. like i stated i've no problem with the relays. they don't disturb my circuit.
     
    Last edited: Dec 2, 2010
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Do you have a schematic of the circuit how the contractor is driven?

    Bertus
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Do you have a snubber diode across the coil of the contactor (relay)?

    Do you have decoupling caps at the uC to hold the power supply steady during load switching?
     
  4. fisho

    Thread Starter Member

    Nov 4, 2008
    18
    0
    dear sir;
    I have a regulated pwr supply(7805 + 100nf filter; main filter cap is 2200mfd) i've also put a100nf cap near the vdd pin of the MCU as recommended. the contactors are driven via relays.the relay circuit is optoisolated from the MCU.the relays switch in and out and no problem. the problem appears as the main 220v contactor energizes and drops.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Do you have a digital scope or other logging device to watch the voltage on the input and output of the 7805 during the load switches?

    An over/under voltage glitch could be causing the 7805 to momentarily block output.

    What is the input to the 7805?

    Is the controller physically near the relay or power lines? If so, it in an enclosure with any shielding?
     
    Last edited: Dec 2, 2010
  6. fisho

    Thread Starter Member

    Nov 4, 2008
    18
    0
    well the input is over 12.5v DC.the pwr supply is far from the micros.
    the amazing thing is that plugging into a remotely located socket outlet
    any kind of load disturbs the micro. my expectation is for some reason the
    MCLR line althogh tied to Vdd via 1K may dip and reaset the micro.still confused.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
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    Verify the presence of an earth ground at the AC socket. If the powersupply is floating with respect to ground, all kinds of strange things can happen.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718

    Can you post a photo of your circuit board, front and back?
     
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