How do I eliminate bad laptop interference?

Discussion in 'General Electronics Chat' started by pcb123, Jul 29, 2014.

  1. pcb123

    Thread Starter New Member

    Jul 29, 2014
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    Hey everyone,

    I've been recently working on a project involving an arduino, some temp sensors, and a relay to power a refrigerator.

    Everything works perfectly when the laptop is not plugged into the charger, but the minute I plug in the charger, the temp sensors are no longer showing up. I am quite certain it's interference either with the laptop or the laptop charger.

    So how can I eliminate the interference? I lost my original charger so I had to buy one online. I bought this one: http://www.ebay.com/itm/261168867318?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

    It is a 2 pin double insulated power supply but I still get way too much interference when it's plugged in.

    Any suggestions? Thanks.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    Did your original charger give the same symptoms, if not then i would replace the charger for a better one.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    Get the picture?

    If your charger makes too much noise then don't use it when using the Arduino. Either precharge it or buy a better charger, one with better noise suppression.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    some of the good laptop manufacturers use shielded cables to keep the interference down and some of the aftermarket mfgrs cut corners on interferance.
    you could try a few ferite clamp on filters on the cords for the supply, and even a few ferite beads on the temp sensor wires right at the arduino. there should be a lot on the net about efi and rfi.
    its not only homemade stuff that acts up around interferance, here the chart recorders that measure oven tempratures jump 10 degrees when anyone uses a portable radio near them.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
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    Yep.. clamp on ferrite beads will be your best friend..

    At work we spend thousands of dollars on EMI/EMC testing and 9 times out of 10 the solution to a failure during testing is to simply attach a few ferrite beads where needed.

    I bought a new LG TV not too long ago and it would randomly turn off.. Well then I remembered the 2 clamp on ferrite beads that came in the box and just wrapped it around the HDMI cable and the power cable and voila.. No more problems.
     
  6. pcb123

    Thread Starter New Member

    Jul 29, 2014
    3
    0
    I lost the original charger so I had to buy the replacement.

    I tried a ferrite clamp on either side of the transformer but it didn't help. Could the transformer itself be the source of the interference?

    How can I determine whether it is the laptop or the charger?
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    It's not just a transformer, but a switch mode power supply operating at a high frequency, which can radiate to other devices. You can often track an interference source with a small AM radio.

    You also might want to design RF interference filters and/or shielding into your circuit.

    ken

    Ken
     
  8. pcb123

    Thread Starter New Member

    Jul 29, 2014
    3
    0
    Ok I'm not very experienced with circuitry or microcontrollers, so are there any resources that help me figure out how to do that? Where would the filters go in the circuit? Would they be between the temp sensors and the arduino or between the resistors and the arduino? Or anywhere else?
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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