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Thread: EMI Affects Teensy 3.6 More Than 3.5 and 3.2

  1. #26
    Senior Member
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    Dec 2016
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    Montreal, Canada
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    spi/i2c isnt designed for long distances, obviously lowering the clock helps, but that is just a bandaid, you’ll also need to handle the reflections using a very small resistance... if this is your “EMI” issue for abusing signals, this thread is pretty much closed

  2. #27
    Senior Member
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    Apr 2017
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    update from my data logging saga...

    based on tips from above (thanks randomvibe) , i'm now able to send data to my display (2.4 inch TFT) reliably. Recall my data logger is in a small electric go-kart with a brushed DC motor--super noisy environment. I've had problems with my TFT going white screen but now it runs fine.

    Here's what we did
    1. use shielded ethernet--5 feet long cable
    2. MOSI twisted with ground
    3. CLK twisted with 3v3
    4. shield grounded to Teensy 3.2 ground through a 1M resistor and a 4.7 nF cap (in series)
    5. shielding NOT tied to display PCB board
    6. I call display.begin() before EVERY display update (which is every second). this allows display to restart as the display gets temp disconnected when the car hits bumps in the road
    7. pullups (4k7 on the display side)
    8. ethernet is around 5 feet long, but I've tried using 12 feet Ethernet and display still worked
    9. home made PCB boards made for data logger which contains the Teensy and display board which mounts the TFT

    Now the next saga is getting SD to write reliably (SD card lot is standalone (no level shifters) soldered to the PCB board, right now it writes like 50% of the time....

    Thanks again to all with these great tips

  3. #28
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    dont forget a very small resistor in series when running long SPI cables on the outputs closest to the source of the MCU SPI lines, to prevent ringing, i know i posted it above just reminding

  4. #29
    Senior Member
    Join Date
    Apr 2017
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    187
    Unfortunately i'm using every one of the 8 wires in CAT5 for display and a few buttons--I sure could use some more conductors.

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