Need help selecting the right components

I am working with a Powerboost 500 charger from adafruit, and am trying to create a UPS for a RasPI using the Arduino to control some automated functions. I have it almost entirely figured out but need some help figuring out the right components.

The Powerboost has 2 pins that I am using, One pin is connected to the Input power from the wall plug. I am pretty sure I can't just connect this to an input on the Arduino. I small part of me thinks I can but I don't want to release the magic smoke, I am thinking I need to use some sort of transistor or relay that either makes or breaks a connection when the power is unplugged (the pin goes low). Problem is i don't know enough to know what type of transistor or relay to use....

Is thus what you want to do

Mike, I'm guessing there is an image there but I can't see it. Last night I got brave (and bored) and decided that since everything shared a common ground I would throw caution to the wind. I pulled the Arduino pin to ground and hooked the Power pin from the PowerBoost straight to. No smoke, Hooray!. Everything appears to be functioning but perhaps I should include some sort of protection?

I'm guessing there is an image there but I can't see it.

It is a link to a You tube video called "Adafruit PowerBoost 500 charger used as a UPS for Raspberry Pi" Which I though was exactly what you were looking for.

for some reason i cant see the link. The power boost with charger can be used as a UPS right out of the box, what I am trying to do is incorperate some intelligent features. I want to have the Pi shutdown aouromatically, disable the output from the powerboost(to conserve power) and turn everything back on when power is restored. I have it working, everything seems okay but its not stable yet. If I run everything with my actual uno board it goes perfect but it doesn't work off board. I have this problem alot. i have a perfboard arduino with headers that I built for fun, and another that I built specifacally for this project. neithr work, some portion of the IO pins are unresponsive, I don't know if its the input or the output but the behavior is slightly different on the two boards, I am going to try and start isolating the issue in the AM

OK, what circuit have you got for the boards? A lot of the circuits on the net miss out the decoupling capacitors because some people think they make no difference but it can cause problems like you are seeing.

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

If you can't see the link then google directly for movies the words:-
Adafruit PowerBoost 500 charger used as a UPS for Raspberry Pi

Actually mike you told me about the decoupling capaciters when i was trying to figure out my first project.

Sorry, but it supprised me how many people don't know about it. :slight_smile:

I'm not even sure if the instructions on the arduino home page include them.

But anyway I've gone over this board for about 2 hours now and can't find anything that looks wrong or differers from past setups. It was working fine but them stopped so I have to assume something went bad. If I pull the ATMega328P It works fine in my Uno Board. I guess I will start replacing pieces one at a time. I did notice when i plug everything in it appears to be workung but only for a moment, any guesses as to which part I should pull first?

Just got it. Defective Crystal!!

Glad you found it.
But

I did notice when i plug everything in it appears to be workung but only for a moment,

Making circuit changes with the power connected is a sure fire way of eventually damaging components.

I am aware, I always power down before removing/adding/changing anything