user43613: I have a chinese arduino nano that I'm planning to use to open a door using a numeric keypad.
My power source is 12V and I want it running 24/7. I have read that the first thing to fail on an arduino is the voltage regulator due to the heat of lowering the voltage to something the arduino can use.
I have think of buying two big resistors of around 1W each to build a voltage divider and only feed 7V to the Vin pin of the arduino, so it will increase its lifespan.
Is this a good idea?

user30175: Terminating voltage by dropping it over large power resistors is a bad idea, efficiency wise. There are better options.
Switch-mode Buck (=step down) converters are usually far more efficient than linear regulators. A linear regulator dumps the excess voltage in a resistor which converts the energy mainly into heat. A switch-mode converter works by switching on/off an inductance at the right time, which is far more efficient.
For step-up/step-down DC-DC converter theory look here, here and here. For a comparison for switch-mode against linear regulators look here.
A step-down converter module like the ones with a LM2596 should be good enough for you. See here on ebay.

43613: <p>I have a chinese arduino nano that I'm planning to use to open a door using a numeric keypad.</p>

<p>My power source is 12V and I want it running 24/7. I have read that the first thing to fail on an arduino is the voltage regulator due to the heat of lowering the voltage to something the arduino can use.</p>

<p>I have think of buying two big resistors of around 1W each to build a voltage divider and only feed 7V to the Vin pin of the arduino, so it will increase its lifespan.</p>

<p>Is this a good idea?</p>
 30175: <p>Terminating voltage by dropping it over large power resistors is a bad idea, efficiency wise. There are better options.</p>

<p>Switch-mode Buck (=step down) converters are usually far more efficient than linear regulators. A linear regulator dumps the excess voltage in a resistor which converts the energy mainly into heat. A switch-mode converter works by switching on/off an inductance at the right time, which is far more efficient.</p>

<p>For step-up/step-down DC-DC converter theory look <a href="https://www.youtube.com/watch?v=m8rK9gU30v4" rel="nofollow noreferrer">here</a>, <a href="https://www.youtube.com/watch?v=QnUhjnbZ0T8" rel="nofollow noreferrer">here</a> and <a href="https://www.youtube.com/watch?v=CEhBN5_fO5o" rel="nofollow noreferrer">here</a>. For a comparison for switch-mode against linear regulators look <a href="https://www.youtube.com/watch?v=giGRrODKJSE" rel="nofollow noreferrer">here</a>.</p>

<p>A step-down converter module like the ones with a LM2596 should be good enough for you. See <a href="https://www.ebay.com/itm/LM2596-DC-DC-4V-35V-to-1-23V-30V-Step-Down-Power-Module-Voltage-Regulator-3A-/251066005460" rel="nofollow noreferrer">here on ebay</a>.</p>
