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I have some brushed motors near to a 433 MHz RF receiver. They're controlled by a 490 Hz PWM signal. The electrical noise they produce is not a problem for the circuit, but it is for the receiver.

How can I reduce the noise, at least on the frequencies interfering with the transmitter?

I read that putting a ceramic capacitor across the motor's terminals and one from each terminal to the motor's case would help; if it's true, what size should they be? I unfortunately don't have technical information about the motors. I'm quite sure they're the same as those, but there isn't much data on that site...

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I read that putting a ceramic capacitor across the motor's terminals and one from each terminal to the motor's case would help; if it's true, what size should they be?

You read the truth. Keep the leads to the caps short. 10nF is a reasonable sort of size, but you can go bigger or smaller if you have other sizes to hand.

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    \$\begingroup\$ Caps to motor case may help if the motor case is well grounded. Otherwise, the whole motor becomes a noise radiator. \$\endgroup\$
    – glen_geek
    Dec 14, 2016 at 16:48
  • \$\begingroup\$ @glen_geek does "grounding a motor's case" means connect it directly to ground? \$\endgroup\$
    – noearchimede
    Dec 16, 2016 at 14:16
  • \$\begingroup\$ @noearchimede no, it means connecting it to PSU ground that's powering it, or the case that's enclosing the equipment, ideally they are one and the same thing. \$\endgroup\$
    – Neil_UK
    Dec 16, 2016 at 14:21

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