Powering the ardunio from an automobile's 12V

I'd like to run my arduino from an automobile's 12V DC power supply. What would be the best way to do this?

I know i can get a cig lighter plug that'll do 5V and plug directly into the power port on the arduino but I'd really like something that I can wire permanently. I've seen some 12V to 5V DC power converters. Are these any good, what other specs am I looking for when I go to buy one of these?

I also would like this solution to be fairly cheap.

Would something from this page work? http://www.mouser.com/catalog/629/1647.pdf

Arduino Playground - WhatAdapter confuses me. According to that I can power directly off the 12V DC from the car (vamp clips from the clock with a fuse in line). Will the internal power reg on the arduino keep the 5V pin outputting close to 5V. If not my analog sensors will be off...or worse, they'll break.

My Arduino USB has a 78M05 voltage regulator on board. That has a maximum input voltage of 35V which is fine for a car. What I'm not seeing in the datasheet is anything that suggests how much power it can dissipate. It has this comforting statement:

The internal current-limiting and thermal-shutdown features of these regulators essentially make them immune to overload.

When running from your 9v power supply and drawing 500mA (the max) you will be burning off 4 volts in the regulator for a 2 watt dissipation. This works. Running from your car when the battery is charging will be something like 14 volts for a 9 volt drop, or 4.5watts. I have no idea if this will dissipate or build up to the point that the regulator safely shuts down from thermal overload.

The good news is that if you only pull, say 200mA then you'll be under 2 watts and are almost certainly fine.

I say try it. Don't get the voltage backwards! If you think it is getting too hot then you can put a couple power diodes in series with the +12v from the car. Each one will knock off 0.7 volts or so, a nice way to make some of the power dissipate outside the Arduino's voltage regulator. Remember to stay above 9 volts on the input to give the regulator room to operate.

Nevermind...man I need to learn to search.

What I'm doing is almost 100% equivalent to this: Arduino Playground - LeadAcidBatteryAdapter

sti robot-

Be careful. Automotive electricity has more noise in it than a can of lightning. Its not exactly the same as connecting an Ard to a Lead acid battery, because the voltage in a car fluctuates quite a bit with the engine speed (alternator). There is noise on those lines from the ignition (~>80Kv, if I remember right). Also, when systems start failing on a car, such as the alternator dying, really really erratic spikes in the voltage are common.

I would add a quick-blow fuse and an external voltage regulator, but thats just me.

I've been running a different device (a GPS engine) in my truck using the same regulator as the arduino (7805) with nothing more than the two recommended filter caps for about 4 years. No problems. I've been running a PIC controlled power controller and another PIC* device on my radio or over 2 years; both use a 7805 with the two recommended filter capacitors. No problems.

Since the arduino uses a 7805 and I think it has an extra filter cap, I would not hesitate to use it in a mobile environment.

Be advised that a 7805 linear regulator has enough overhead that, over time, it can kill your car's battery. If it's a small load and you drive every day, no worries. If you have a small battery or drive infrequently or draw a lot from the 7805, make sure you don't leave it on for extended periods when the engine isn't running.

-j

*Why PIC? One PIC was in a kit and the other I built before I learned about the arduino. I plan to replace both with a single AVR, developed using the arduino, as soon as I get time....