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I am trying to design my first PCB with a microcontroller and SMDs. I am using two crystals; one is 25 MHz, the other one is 16 MHz. I tried to put them close to their MCU.

  • Can these crystals affect each other if they are that close to each other like this ?

  • Can these crystals be affected by a relay? This is my relay's schematic: raspberrypiforum (the right bottom three pins are 24 V input pins).

enter image description here

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  • \$\begingroup\$ They look like crystals, not crystal oscillators. Two different beasts. The relay shouldn’t affect the crystals but it really depends on your pcb layout. The crystals should be surrounded by a 0V track or copper pour. \$\endgroup\$
    – Kartman
    Dec 24, 2021 at 10:21
  • \$\begingroup\$ @kartman thank you. I will surround them with ground plane. I wrote crystal now sorry. I am using crystals . \$\endgroup\$ Dec 24, 2021 at 10:36
  • \$\begingroup\$ Without seeing the MCU location I'd say the crystals are way too far from it and from capacitors as well. \$\endgroup\$
    – Maple
    Dec 24, 2021 at 15:44

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Relays can generate very sharp and high EMI transients (depending on the load). It is possible that these could couple to the crystals and corrupt your MCUs clock.

If you are switching high loads (or AC mains loads), put a snubber across the relay terminals.

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  • \$\begingroup\$ Thank you, I am using 24V DC on terminals. \$\endgroup\$ Dec 25, 2021 at 5:35

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