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I am trying to switch on a G5Q Relay on a Genuino MKR1000. I am able to do it using VCC (3.3v) but not with Digital I/O pin (Also 3.3v) this is because the current from digital pin is lower(7mA). I am new to electronics. How can I boost the current to the relay without damaging my board?

Kashif
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    Check sources like Aliexpress and buy a relay module. – Wouter van Ooijen Sep 17 '16 at 16:17
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    This appears to be a duplicate of http://electronics.stackexchange.com/a/203906/9006 Also, web search engines provide a lot of results by searching for "controlling relay with arduino". There are also likely answers on http://arduino.stackexchange.com/ Please read the [help] to understand how to ask good questions. This question will likely get closed as a duplicate. – gbulmer Sep 17 '16 at 16:37
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    Possible duplicate of [How do I increase the drive current from the arduino digital pins?](http://electronics.stackexchange.com/questions/203903/how-do-i-increase-the-drive-current-from-the-arduino-digital-pins) – Armandas Sep 17 '16 at 22:24
  • Possible duplicate of a hundred questions. ... – Passerby Sep 18 '16 at 06:18

1 Answers1

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Although this is mostly a duplicate of "How do I increase the drive current from the arduino digital pins?" as kindly commented already, there is another point to address in your question.

You said:

I am trying to switch on a G5Q Relay on a Genuino MKR1000. I am able to do it using VCC (3.3v)

The lowest coil voltage G5Q relay has a nominal 5V coil - not 3.3V. The fact that yours operates at 3.3V is not guaranteed and will be affected by things including temperature, internal wear etc. The G5Q datasheet I linked above shows that Omron guarantee the relay will operate at 75% of nominal coil voltage = 3.75V for a 5V coil. Therefore, as I said, your relay is not guaranteed to operate at 3.3V.

You may also find this previous question interesting, about operating relays at reduced voltages: "Is it OK to use a lower voltage to operate a relay coil than rated coil voltage?"

Therefore your situation seems to require:

  • an suitable external driver (e.g. transistor) and freewheeling diode, to drive the relay coil (see the first linked question above) from the 3.3V digital output of your board; and

  • a suitable power supply voltage for your relay.

    That means using a 5V supply for a 5V relay, if you expect reliable operation. From researching your MKR1000 board, I see that 5V is available when the board is powered via its USB or Vin connectors. This could be used to supply a 5V relay coil (assuming a suitable current rating of that power supply). Don't use the 3.3V supply which you mentioned, to directly power a 5V relay.

    However when the board is powered from an attached LiPo battery, then only the 3.3V supply voltage is available. A boost regulator could be added to generate 5V from that 3.3V input, and the generated 5V could be used to power a 5V relay. I could not find documentation stating how much current your board can supply at 3.3V (to power a 5V boost regulator and relay) in that situation. The answer will be related to the 3.3V regulator IC (AP7215-33YG, according to the board schematic) and how much current the board already uses, from the 600mA maximum which that regulator can supply according to its datasheet.

So in summary: The way forward depends on how you intend to power your board. I just wanted to highlight that powering a 5V relay from 3.3V (even when you think it works, as you stated) can result in problems.

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SamGibson
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  • IO pin supplies 7mA at 3.3v while the relay takes 30mA at 5v – Kashif Sep 18 '16 at 13:08
  • @Kashif - "IO pin supplies 7mA at 3.3v while the relay takes 30mA at 5v" - That difference in *current* required vs. available directly from the pin, is why you need to use an external driver (e.g. BJT, MOSFET etc.). (FYI the relay's rated current is *40mA* @ 5V according to the datasheet I linked.) You should never try to power a relay *directly* from an I/O pin. How to handle the difference in *voltage* is what I tried to explain in my answer. Again, the voltage at the I/O pin is only part of the story (you don't power a relay from an I/O pin!); it is the power supply voltage which matters. – SamGibson Sep 18 '16 at 13:35
  • [continued] If you have a specific question about something which is not clear, please ask it. – SamGibson Sep 18 '16 at 13:38