I bought a 5 V Relay Board: LINK (Aliexpress) and just realised it's "Active LOW". I want to control a water pump via a Arduino Micro.

I tested it and as far as i understand the workings of this relay, putting the pin to LOW activates the little LED on the Relay Board and switches to the NC position where I connected the water pumps ground wire.

I don't feel very comfortable with that because normally those relays are activated by setting the pin to HIGH. I tried to connect the ground wire of the pump to the normally open position but than, if I disconnect the Arduino to simulate a malfunction the pump keeps running.... this doesn't happen with the first configuration.

So my Question: Is it a problem to use the Relay Board in the way described above (Pin to LOW switches Coil to NC Postion). Is there a way I'm not seeing to get the Board to switch the Coil if a pin is set to high.

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    Is there a way I'm not seeing to get the Board to switch the Coil if a pin is set to high .... why would you want to change the board? .... changing the arduino sketch is way easier – jsotola Jun 24 '18 at 0:09
  • yeah you're right I just thought about maybe some kind of "jumper" configuration or powering the whole board via an Arduino ping or stuff like this – Peter S Jun 24 '18 at 8:13
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    I don't quite understand what kind of problem you expect. Could you draw a schematic and explain what you think could happen? – Dmitry Grigoryev Jun 25 '18 at 7:40

That relay module is driven by optocouplers. You are just driving and LED, and that is connected though a resistor to VCC.

In the past it was common to use active low for driving things since an N channel MOSFET could typically sink more current than a P channel one could source. Also in the days before CMOS there was really only low-side (sinking) switching, so active low was the norm.

These days it's not necessary, but it's still common because that is how it's always been.

So yes, active low is both common and accepted.

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