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I am transmitting a PWM signal from a 8051 to an L293D DC motor driver. I am planning to perform this using cables and this cables will be at most 2 meters. And the frequency of the PWM signal is around 1 - 2 kHz. Is it likely that it will pass EMC?

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  • \$\begingroup\$ Depends purely on how sharp your rise and fall times are. \$\endgroup\$ – Jack Creasey Dec 18 '17 at 16:36
  • \$\begingroup\$ I am sending square waves actually and did not check the rise and fall times. Did you refer to sawtooth waveforms or something that is not a square wave? \$\endgroup\$ – İlker Demirel Dec 18 '17 at 16:38
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    \$\begingroup\$ @İlkerDemirel all square waves have a finite rise/fall times. Though we sometimes assume they area ideal, with 0 rise/fall times to simplify calculations, this isn't the case in practice. \$\endgroup\$ – Jim Dec 18 '17 at 16:42
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Start here.

  1. If you consider your PWM signal fundamental freq frame rate then you have a series of odd harmonics of diminishing amplitude starting from here.
  2. Once you leave 50%, then for the shorter and longer period you will have an additional series of odd harmonics starting at the base freq for each half.

Depending on the rise and fall times you will have a lot of odd harmonics.
You can control the harmonics by introducing slew rate control on your output.

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