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I have a relay that I can activate it with a PIN to GND.

I have connected that relay to a separate power supply, different from the used for the raspberry. As I have read, I can't supply GND using GPIO due to LOW is not the same as GND.

How can I activate that relay that only is activated by GND?

EDIT: Event I would able to supply GND from RPI, the relay doesn't work. In order to work I need to join the GND from external power supply and RPI but this causes false positives in some GPIOs when reading from them

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    We need to know the specs of the relay. Without that it is guess work as to how to operate the relay. – joan Oct 25 '17 at 10:50
  • It's hard to know because it's a chinese relay with chinese labels ^_^ but I have connect the power supply to 5v and the activation pin when it goes to GND the relay get activated – RuBiCK Oct 25 '17 at 10:53
  • the relay is similiar to [this one] (aliexpress.com/item/…), with no specs :( – RuBiCK Oct 25 '17 at 11:03
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Connect Pi ground (say pin 6) to relay ground, Pi 5V (say pin 2) to relay VCC. Connect relay IN carefully to alternately pin 1 (3V3) and pin 6 (ground). If the relay operates you are good to go using a GPIO. If it doesn't operate it is incompatible with the Pi.

  • It gets activated with 3v3 and GND (I don't know if it's normal) it's better activate it with vcc or gnd?. I don't like to connect a relay directly to the GPIO due to power consumption... – RuBiCK Oct 25 '17 at 19:03
  • That should mean you can connect a GPIO to the relay IN pin (leave relay ground and VCC connected to Pi ground and 5V). Then switch the GPIO low to activate the relay or high to deactivate the relay. The relay should need only a few milliamps from the GPIO. – joan Oct 25 '17 at 19:38

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