bike power - hall effect current sensor

I am working on a bike power project, and i'm just starting to get into world of arduino, so any help is much appreciated.

I want to measure 12v dc current at two points; supply and load to a deep cycle battery. using two (hopefully inexpensive) hall effect sensors, i wanted to use the arduino to compare the current reading in to and out of the battery and to activate two different sets of lights depending on the result of the comparison eg. more power going in than out turns on a green light, more power going out than in turns on a red light.

i have seen a whole load of hall effect sensors out there and am not sure which to use or how to build the circuit. would i need to amplify the signal from the sensor before it reaches the arduino?

any help welcome on hardware/circuit diagram/code to make it work...

thanks in advance.

Look at this current sensor and get the data sheet, page 10 has some typical circuits:-
http://uk.farnell.com/allegro-microsystems/acs712elctr-05b-t/sensor-current-5a-soic8-712/dp/1329623?_requestid=261000

more power going in than out turns on a green light, more power going out than in turns on a red light.

You can't measure power in / out at the same time because it doesn't happen like that. Current is either going into the battery or coming out of it so all you need to do is sense the polarity of the current flow.

thanks, I'll check it out.

ok, so i have one on order, does anyone have any advice on the code side of things? possibly something existing i could adapt?