Is it a bad idea to run arduino continuously off a car battery? The battery is not in a car. I was thinking I would hook up a separate 5v reglator like in this tutorial (Beginning Embedded Electronics - 1 - SparkFun Electronics) before the controller to reduce strain on it. I also read that the car battery is a noisey source and that the circuit in the tutorial will reduce some of that.
Car batteries aren't noisy in and of themselves; its when you are using an automobile's power system when the noise comes in, because of the inherent noise of the charging system, the starting system, and most especially, the ignition system (sparks being needed, which require high voltage pulses, which set up induced currents and noise in other parts of the electrical system).
With that said, the only thing you should worry about is the fact that the 7805-like regulator used on the Arduino has to dump the extra voltage from the car battery to regulate it; that extra goes away as heat. Now, with the 7805 this is only a real issue from a efficiency perspective, but we don't have to worry about that with a car battery much. But the heat issue should be dealt with - via a heatsink. This is where using a second regulator (or a switching power supply) to drop the voltage down prior to the Arduino would come in handy, because you could mount that regulator on a heatsink instead (or eliminate it entirely with a switching power supply). Just be aware that if you plug into the barrel jack of the Arduino, your voltage must be above 7 volts for the on-board regulator to regulate properly, so a 7805 here would not be good (a 7808 or 09 would be OK). Mount it on a proper heatsink, and add the proper capacitors, and it will work fine. Otherwise, if you want to use a 5 volt source (whether a regulator or a switching power supply, like a PC power supply), you would have to feed that voltage into the voltage input pin on the Arduino - after the on-board regulator (I think it is marked Vin - but check the schematic first).
I'm glad you mentioned that because I thought the Vin pin (I'm using an uno) could accept up to 12v. Is that not the case?
The battery will be powering a few strings of LEDs. They'll consume no more than 2W at most. The arduino will be controlling the LEDs via PWM and a few NPNs since the lights require more current than the arduino can supply. The arduino itself will be using a very minimal ammount of power. Just enough to signal the transistors.
One of the reasons I liked the idea of using the external regulator is, as was mentioned, heat. The controller will be running 24/7 so I figured putting the 7805 through that punishment would be a better idea.
That would definitely be ideal. unfortunately, I'm on a bit of a time constraint so I'll most likely be going with the external 5v regulator and perhaps upgrading later if heating or wasted power becomes an issue. Two PV panels will be bringing in a minimum of probably 10-20 Wh @ 12v in the winter to charge the battery. As long as the regulator+lights+arduino doesn't eat up that much in the four hours per day the lights are active, I should be okay.
ryry:
That would definitely be ideal. unfortunately, I'm on a bit of a time constraint so I'll most likely be going with the external 5v regulator and perhaps upgrading later if heating or wasted power becomes an issue. Two PV panels will be bringing in a minimum of probably 10-20 Wh @ 12v in the winter to charge the battery. As long as the regulator+lights+arduino doesn't eat up that much in the four hours per day the lights are active, I should be okay.
If you go with an external 5V regulator, you'll want to feed its output to the +5V pin (see the schematic - I was wrong, the Vin pin goes to the input of the on-board 5V regulator, while the +5V pin is -after- the 5V regulator). You can't feed the output of your external 5V regulator into the input of the barrel jack or the Vin pin, because the on-board 5V regulator needs a minimum of 7 volts to operate properly (however, if your external regulator was a 7808 or 7809 - that would be better - you wouldn't need as large of a heatsink for it, either).