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The relay module consists of two sets of pins:

Set1: GND, VCC, Int1, Int2 Set2: JDVcc, VCC, GND

In set 2, VCC and JDVcc are jumpered together normally, which is removed to power the relay coil with external supply.

However, can I supply 5v directly from external source to the VCC pin of Set 1 and connect the GND pin to common ground, leaving the VCC and JDVcc pin jumpered together as they are? It's because I am running out of pins in my Uno.

Will that work?

closed as off-topic by Chris Stratton, Majenko, gre_gor, Code Gorilla, Greenonline Jun 21 '17 at 14:44

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  • if you leave it jumpered, you will re-use the control's VCC to drive the relay. If that supply has enough current, that's a fine way of doing it. Don't mess with the grounds; they have continuity already... – dandavis Jun 21 '17 at 4:05
  • @dandavis it s a arduino module so i guess its designed to take in low current bcoz arduino ports can supply only 20mA. – Rudranath Palit Jun 21 '17 at 4:08
  • check the datasheet for the holding current of what i'm guessing is a common 5v songle relay. probably ok. – dandavis Jun 21 '17 at 4:10
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    I'm voting to close this question as off-topic because it is about relays and has nothing to do with Arduino, and provides insufficient detail to be answerable anyway. – Chris Stratton Jun 21 '17 at 5:31
1

can I supply 5v directly from external source to the VCC pin of Set 1 and connect the GND pin to common ground, leaving the VCC and JDVcc pin jumpered together as they are?

Probably you're using this relay module, which is fairly common:

Relay module schematic

If that's the case, then the answer is YES as long as you keep all grounds tied together and the 5V external supply deliveries a voltage reasonably close to the Arduino 5V.

Why?

  1. When IN is high and VCC is close to 5V, there isn't enough voltage difference for forward biasing the diodes. They won't conduct and no current will flow from or into your Arduino data pin.

  2. When IN is low, the diodes are forward biased and current will sink into the Arduino data pin. As long as VCC is close to 5V, the current limiting resistor will keep current within specification of what the Arduino data pin can tolerate.

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