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I use PI 4 to power two 3v relays. One is controlling 5v dc, another 12v dc. And about once a minute I am switching each relay signal state to On/Off So each relay is connected to 3v pin, ground pin and signal GPIO on the PI. Do I need to put some protection, like resistors, diodes on the board? What exactly? Or is this setup safe? I tried to google the answer but did not find any information on pi+3v relays My relays are these ones

Here is my board attached. enter image description here

Thank you in advance!

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    The only thing I can add to the answers you have is this: In general, you should avoid buying electronic components from vendors who do not provide a spec sheet. The information provided on the Amazon seller's page is incomplete and unreliable. When driving anything directly from a GPIO pin, you should know how much current is required. This due to the fact that the GPIO gates are rather wimpy, and poorly documented.
    – Seamus
    Dec 29, 2020 at 21:24

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The relay modules contain all the protection needed for the Pi. There is no need to do anything else to protect the Pi.

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No one can say because the linked page has ABSOLUTELY NO specifications.

Caveat emptor!

Using a relay AND an opto-isolator is NONSENSE and indicates whoever "designed" the module has little experience or understanding of circuit design. The opto-isolator just adds inefficiency.

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  • Though isolation is not required, why not use an opto instead of a transistor? The difference in efficiency is negligible as the relay coil is the major factor. Those few mA required by the opto are much less than the coil current.
    – Sim Son
    Dec 31, 2020 at 22:53
  • @SimSon you need ~15mA to drive an opto-isolator, which is close to the GPIO per pin max and uses a significant part of the 50mA total available AND you need a transistor to drive the relay.
    – Milliways
    Dec 31, 2020 at 23:12

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