Hello, everybody
Can I use the VIN and GND powerpins on my Arduino Uno to power my Arduino (with a 6 AA batteryholder)? Otherwise I'll have to buy a 2.1x5.5 mm powerplug and solder this to my batteryholder.
Thanks for any help,
Superpelican 
Yes that will work. Just be sure to measure or careful inspection if no meter for correct polarity before wiring to the Vin and ground pins.
Lefty
So, that means that the Powerpins are connected to the Voltage Regulator, so I won't damage my Arduino?
So, that means that the Powerpins are connected to the Voltage Regulator, so I won't damage my Arduino?
Yes, the Vin wires to the input of the on-board +5vdc voltage regulator, just like the external power connector does. Vin can be used as an output for voltage if using the external power connector, or as an input for voltage as you want to do. Vin must be around +8vdc or higher, but the closer to 8volts the less heat will be generated by the regulator.
Lefty
Actually it works down to 6.8v until the 5v starts dropping.
If you have a power source that delivers 6V or less you could connect that directly to the 5V pin of the arduino via a 1N400x diode. The diode has a voltage drop of .7V and the atmega can be safely driven with up to 5.5V
So, @smeezekitty, I can safely power my Arduino with my 6 AA batteryholder, wich delivers 7.2 V (as I am going to use 1.2 V NiMH rechargeable batteries)?
Thanks for all the help everyone,
Superpelican
Actually it works down to 6.8v until the 5v starts dropping.
The issue isn't just the drop out voltage rating of the regulator. The arduino has a auto-voltage detector/selector circuit wired as a opamp comparator. The external voltage input has to be high enough to trigger this selector circuit to select external voltage over USB voltage. There is also a series polarity protection diode between the external voltage connector and the input of the regulator, which drops a little voltage. There is a critical voltage value which if below that value the voltage selector circuit will not switch to external source.
Lefty
In a battery powered project I'd always go for a way to feed the arduino directly with regulated 5V. The voltage regulator has a pretty bad efficiency.
A switching regulator is the way to go when you don't want to use your precious battery power to heat your arduino.
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BTW: A cheap way to get a 5V power source are the USB power packs you can buy to charge your phone/mp3player on the go. They contain a lithium battery, a 5V step up regulator and a charging circuit. You can get them for about 10$
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So I also can power my Arduino with a 9V battery+clip instead of the 6 AA the same way? Without blowing my Arduino of course!
,
Superpelican
Yes but be aware a 9v battery has a very limited capacity and won't last very long.
Yes but be aware a 9v battery has a very limited capacity and won't last very long.
And they are the most expensive battery you could use from a mah capacity point of view. They go for around $2.50 each at my local drug stores.
Lefty
Yes, I already heard that when you feed your Arduino with a 9V they don't last long. But it is only until I have a 6 AA holder.
Thanks,
Superpelican