I have built a device using the arduino that I want to install in the back of my car. In the back of my car I have an amplifier to power my subwoofer. The amp has two thick wires running to the car battery to power it. I was wondering if I could somehow power an arduino off of these wires. The arduino needs to be close to the amp. Ps I am designing the device with an integrated arduino(Atmega 328). So extra components can be included. Schematics would be greatly appreciated if need be.
On a side note does anyone know where I can find a schematic to have the arduino(Atmega 328) on it's own i.e. The arduino would be pre programed and put on a pcb.
Any help would be greatly appreciated.
Well according to the Deumilanove & Uno data sheet it can take voltages of between 7-12 V with it's limits being 6-20V so technically you should be able to supply from the car battery to the Arduino on that basis. Theoretically all you should need to do is wire a connector to plug into the board and off you go.
Don't forget though a 12V car battery could be closer to 14V as it's charging or nearly full so you might be starting to push the board a little at that stage which will result in heat so some sort of regulator would probably help.
Other option is to look at something like a phone charger that uses the cigarette lighter (12V supply) which will output something in a more desirable range (usually 5-9V for a phone) - just lop off the connector, put a new one on and off you go. I have done this to recycle a lot of old phone chargers (AC) which make nice Arduino power supplies without buying new ones and land filling the others.
ajfisher has a good suggestion in using a charger or other device developed for automobile use. Besides the typical 14V voltage level, power on cars is very noisy with potentially high voltage spikes.
If you decide to run your Arduino directly off the car supply, put a Varister, Transzorb, TVS or other protection device across the Arduino power input. I would suggest one in 18-19V range.
Powering directly off the car battery is generally a bad idea. You can add lots of other components to make it safe to do but you might as well, as mentioned above, take a commercial product (phone charger or similar) which can turn the battery voltage into something a bit nicer (maybe even regulated 5V).