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RC filter for cars — Parallax Forums

RC filter for cars

generatorgenerator Posts: 7
edited 2004-09-09 13:40 in BASIC Stamp
Anyone have a diagram in their archives of what value caps and resistors to use to make a filter to supress engine noise going into a basic stamp?

Comments

  • KenMKenM Posts: 657
    edited 2004-09-09 03:21
    What signal, voltage line of the vehicle are you monitoring and from exactly where on the car.....

    Example, are you picking up battery voltage from the ignition coil, fuse box, at the ECU, or where..

    Please give more detail.

    Ken
  • jakjrjakjr Posts: 88
    edited 2004-09-09 04:54
    Dont know if this helps any but I suppose it might or should anyways.

    My electric planes motors use·two .1 uf caps, a .49 uf cap, and a shotkky diode to filter noise and supposedly make the motor more efficiant,

    The diode isnt part of the filter, its just supposed to make the motor more efficiant and make it run cooler, dont know if it really does anything though·rolleyes.gif .

    The two .1 uf caps have 1 lead soldered to each power terminal and the other grounded to the motor case. One lead of the .49 uf cap is soldered to the·+ terminal and the other lead to the - terminal.

    One lead of the diode is soldered to the + terminal and the other to the - terminal.

    Hope it helps.
  • steve_bsteve_b Posts: 1,563
    edited 2004-09-09 13:40
    If you have a scope, hook it up and see what kind of noise you are getting (frequency/amplitude).

    Then just experiment.

    I had a 200ft RS232 run from my BS2 (accelerometer) and had terrible noise on the line.· I just played around with some resistors and capacitors until I had a good signal (or a BETTER signal!).

    Because my run was so long, I had to be careful what resistor value I used (dampened my signal too much) and the cap value was just there to smooth out those noisey pulses.
    Start with a 1k resistor and play around with some caps.
    Even use a potentiometer and that'll give you a bit more tunability (is that a word?! turn.gif )
    A tunable cap would be good too (careful that it doesn't short at one end of it's adjustment -- you'll drop all your signal to ground which might pull too much from it's source and damage it).

    Someone else might have a more scientific means of doing this....but if you don't know where your dirt is coming from, you won't know what to use to clean it.· So, without a scope you'll have to do it by trial and error.
    If you weren't plugged in to a car....then I'd say your noise was probably mains power (60Hz) which would be easily sorted out.

    Good Luck

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    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
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