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Embedded System in Noisy Environment

Discussion in 'Electronic Design' started by Rich, Apr 13, 2005.

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  1. Rich

    Rich Guest

    We've developed a Microcontroller System for automotive use with few
    sensors and a solenoid valve control output via a Relay.
    We've found these valves resets the microntroller used (ATmega128) when
    opening or closing and partially solve the problem with a diode in
    parallel of the solenoid.
    Moreover, in seldom cases the progam resets or loose it's variables
    (counters) stored in eeprom.
    Voltage regulation is based in a LM2574 switcher. We have not
    implemented further filtering circuits and our housing is made of
    aluminum.
    In my understanding we need some EMI shielding, or power line filters
    to avoid the reset problem.
    Any advise is appreciated.

    Rich
     
  2. Joerg

    Joerg Guest

    Hello Rich,

    This could have a lot of causes. Besides reviewing the grounding you'd
    have to measure VCC at various places, then measure whether any sensor
    input spikes into the processor's substrate diodes etc. But this is
    easier said than done because you have to avoid creating a ground loop
    with the scope. If you try this yourself make sure to do "sanity
    checks", for example touching ground with the probe tip and verifying
    that no spike is seen while doing that.

    If you aren't familiar with EMI I suggest to hire a consultant to help you.

    Regards, Joerg
     
  3. I doubt either of those will solve your problems, and if they do it
    will only be by chance. It's really necessary to take a look at the
    overall system to see where the problems might be coming from. At a
    minimum you're likley going to require a new PCB layout, though it's
    sometimes possible to band-aid a solution for a few units.


    Best regards,
    Spehro Pefhany
     
  4. Genome

    Genome Guest

    Yes, I can't help you.

    You see my name is God and, for some strange reason, I have never
    experienced similar problems.

    I gave up looking for jobs a while back after I was made redundant.

    I went to quite a few interviews but the people always seemed to be
    interested in problems similar to your own.

    Unfortunately I don't have experience of them.

    I think I fucked up somewhere.

    DNA
     
  5. Guy Macon

    Guy Macon Guest

    Go to [ http://www.guymacon.com/SUN/INDEX.HTM ] and scroll down to
    the section titled "Industrial washing machine control."
     
  6. Mark

    Mark Guest

    i agree with what guy said....

    is the diode that is in prallel with the solenoid monted directly at
    the solenoid.

    I also find a 0.1 uF cap at the base to ground of the switching
    transistor slows thing down a little to reduce spikes.

    Mark
     
  7. Rich

    Rich Guest

    Thank you all for your advice.
    Guy's article is very illustrative of where the problem is. Moving
    the diode from the board to the solenoid was tried in the past and
    work. In order to avoid the user to place a diode at the solenoid we
    soldered it on the board, but as you explain:

    "Electrically it was the same circuit, but the +5VDC spike went from
    30 volts to around half a volt. The collapsing magnetic field was
    creating a current that recirculated through the diode, and the wiring
    between the solenoid and the diode was acting like a big loop antenna,
    broadcasting the spike into the electronics. By placing the diode on
    the solenoid, the size of the loop was made much smaller"

    Is it a possible solution to keep the diodes on the board, and enclose
    it in a copper Faraday Cage?
     
  8. That may actually make it worse, because of coupling to the board.


    Best regards,
    Spehro Pefhany
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Is your problem that the solenoid is case GND'ed so that it is not
    possible to use twisted pair power lines to it? And the solenoid is
    switched in/out by a relay?- That creates a helluva mess with relay
    bounce of power to the solenoid which can be on the order of solenoid
    current rise/fall time.
     
  10. Nico Coesel

    Nico Coesel Guest

    I always power relays from a filtered power supply (using a diode,
    resistor and capacitor). This prevents spikes going back into the
    circuit. Also, a switcher may not like the sudden extra current drawn
    by the solenoids. The capacitor will help to overcome this.
     
  11. Rich

    Rich Guest

    Solenoid is about 4-5 feet from the uController system. Yes, solenoid
    case is grounded to the truck. The other line goes to a relay in the uC
    system wich switch 12VDC from the truck battery.
    We use an optocupler between the uController and relay to drive the
    solenoid.
    I found some systems using Pi-Networks to filter power lines to the
    system and an excellent AN at Littlefuse named
    AN9312 - Suppression of Transients in an Automotive Environment.
    http://www.littelfuse.com/cgi-bin/r.cgi/know_file_detail.html?LFSESSION=yoMURlJITi&FilebaseID=91
    We'll implement these devices to the system field test and show the
    results in the group during in the next days.
     
  12. Rich

    Rich Guest

    Rich ha escrito:
    We added a Pi-Network at the voultage input and the problem was solved.
     
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