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I am building a small automated indoor greenhouse. I want to use an Arduino Nano to control some LEDs und a fan (both through relays) and a water Grove Water Atomization module. Everything works fine, as long as I power the LEDs and the fan with a 12v supply (3 watts) and the Nano through USB. But I want to power the Nano through the 12v supply, too.

So I built a voltage divider that delivers 7.25v. I measured it with a multimeter. But when I connect it to the VIN of the Nano, the voltage drops to 1.16v. Wich – of course – means that the Nano doesn't start. When I tried it, only the Nano and the relays were connected to the 12v power supply. The relays through voltage divider delivering 5v.

I tried it with an original Arduino and a chinese compatible and got the exact same result both times.

Does anyone have an idea, what I am missing?

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You just can't use a couple of resistors to deliver a reliable voltage source like that. The voltage divider effectively works as advertised with zero current. Your Nano will take more than zero current. See here for one discussion.

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    Ah, okay. So I really missed an important detail. Thanks a lot. I just tried a step-down converter and it works like charm. Commented Jul 26, 2022 at 8:28
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If you do not place more than a few mA load on the Nano 5V pin you can wire 'Vin' directly to 12V. Your resistor idea sounds great however when you add the fluctuating current requirement you cannot get a stable output it will change with the load. Note the divider circuit resistance has to be very low in value to stay close making it not practical.

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  • Yes, I know. I tried that first. But the voltage regulator of the Nano got quite hot, I guess the water atomization module draws too much current. Commented Jul 27, 2022 at 20:03
  • Try it without the atomizator. I have a feeling it will stay much cooler.
    – Gil
    Commented Jul 27, 2022 at 21:36
  • The heat wasn't the only problem with the atomizer. Whenever it was attached to the Nano, the Nano froze after some minutes. I added the step-down converter to supply 7 volts to VIN, which helped with the heat, but the Nano still froze. So I added a voltage regulator, to bring the 7 volts to 5 volts for the atomizer. Now everything works fine. And no element gets hotter then 34°C. Commented Jul 28, 2022 at 22:29

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