user29438: I'd like to build a reverse car sensor using Arduino
When we select reverse gear, the reverse lights powers, so we can take electricity from them.
My question is can i power my Arduino directly from the reverse lights wires, or should i use regulators or anything else?

user29234: Use a switching regulator such as the LM2596. You can get a ready board from eBay for about US$1


user4143: It depends very much on the car and your Arduino. There are two factors to consider:

Leeching power off lights can have an adverse effect on the car's ability to sense a blown bulb.
Many Arduinos have a 2 second delay while the bootloader executes (some even have 8 seconds).

If your car doesn't sense blown bulbs (most modern ones now do, even cheap ones) and you can work without a bootloader (programming directly with a USBasp for example) to avoid the power-on delay, then it may be possible, yes.
As has been mentioned by others, using a switching regulator is the best method for powering the board as it avoids excess power loss through heat (which can especially be a problem in confined spaces). I would recommend not using one of the cheap eBay modules, but instead using a proper "cigarette lighter" to USB adaptor (available from all good gas stations priced $5) which is designed to work with automotive voltages. A car's 12V power has transients in excess of 50V sometimes (back EMF from the spark generation) and the electronics have to be able to cope with that - those cheap eBay modules aren't designed for that and could die taking your Arduino with it.

29438: <p>I'd like to build a reverse car sensor using Arduino</p>

<p>When we select reverse gear, the reverse lights powers, so we can take electricity from them.</p>

<p>My question is can i power my Arduino directly from the reverse lights wires, or should i use regulators or anything else?</p>
 29234: <p>Use a switching regulator such as the LM2596. You can get a ready board from eBay for about US$1</p>

<p><a href="https://i.stack.imgur.com/0xzjG.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0xzjG.jpg" alt="enter image description here"></a></p>
 4143: <p>It depends very much on the car and your Arduino. There are two factors to consider:</p>

<ol>
<li>Leeching power off lights can have an adverse effect on the car's ability to sense a blown bulb.</li>
<li>Many Arduinos have a 2 second delay while the bootloader executes (some even have 8 seconds).</li>
</ol>

<p>If your car doesn't sense blown bulbs (most modern ones now do, even cheap ones) and you can work without a bootloader (programming directly with a USBasp for example) to avoid the power-on delay, then it may be possible, yes.</p>

<p>As has been mentioned by others, using a switching regulator is the best method for powering the board as it avoids excess power loss through heat (which can especially be a problem in confined spaces). I would recommend not using one of the cheap eBay modules, but instead using a proper "cigarette lighter" to USB adaptor (available from all good gas stations priced $5) which is designed to work with automotive voltages. A car's 12V power has transients in excess of 50V sometimes (back EMF from the spark generation) and the electronics have to be able to cope with that - those cheap eBay modules aren't designed for that and could die taking your Arduino with it.</p>
