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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?

meyer_mit_ai
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2 Answers2

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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.

Nick Gammon
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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.

Gil
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