Battery and wall wart connection

[jasonandkids]

Hello,
Is it possible to connect both positives from a battery and wall wart, then connect both negatives to a nc/no switch? 
I am trying to power my project with either battery or a wall wart.
Thank you,
Jason

[CrossRoads]

Connect the Gnds together and to the Arduino.
Connect one positive each to NC and NO, and the Common to the Arduino.

[Chagrin]

See also http://www.ti.com.cn/cn/lit/ds/symlink/lm1117-n.pdf figure 37 for ideas.

[jasonandkids]

See also http://www.ti.com.cn/cn/lit/ds/symlink/lm1117-n.pdf figure 37 for ideas.

I am new to electronics, and am confused by your post.  How would any of those devices help me?  Do I need to have another device for my project, or will my NO/NC switch work by itself?
Thanks

[Chagrin]

Your switch will work by itself. The advantage of the type of circuit I linked above is that it will automatically fail over between the wall power and battery when either is removed -- no switching required.

[jasonandkids]

What would the best way to automatically switch between battery and wall wart?  Could I use a PNP?
I would like the battery to be used if the wall wart is not plugged in.
Thanks,
Jason

[mirith]

See also http://www.ti.com.cn/cn/lit/ds/symlink/lm1117-n.pdf figure 37 for ideas.

I'd possibly look at figure 37 as suggested before?

[jasonandkids]

I am a little confused by figure 37.  I am new to electronics, and do not understand the schematic.  Do you know of another site that might explain it further?

Is it not possible to use a PNP (or something similar)?  If I connected the wall supply to the base of the PNP and connect the battery to the Collector, wouldn't that switch off the battery supply, whenever the wall supply is added?   Attached is a crude drawing of what I was referring to.

Thank you,
Jason

[mirith]

Your described circuit probably won't work, but you could probably do something with a relay.  Basically when plugged into the wall, you'd need to disconnect the battery and connect the supply.

[jasonandkids]

What about it wouldn't work?
Should I be looking at the LM117?
What if I added 2 diodes like attached?
Thanks,
Jason

[mirith]

Actually, that might work.  I didn't have time to think closer about your original circuit, but this later one makes a lot more sense with the diodes.  I would just make sure to use low voltage drop diodes, and make sure both will supply enough voltage to drive your regulator after you drop the voltage cross the diode (and the transistor, but that should be less significant).  Don't forget the resistor to the base of the transistor, or you'll release the magic smoke.