Hi. Ive set up a small portable tempreture logging device to record and log the temperature. i'm using the SD card on the ethernet shield attached to the arduino uno to log the data. the data logging process works just fine when it is powered with a external wall (9v) supply, but the moment i use a 9v battery to power the device, it stops working and no data at all is logged - bnot even a file is opened or created. can any one explain this to me? is the battery not suffiecient enough power supply?
is the battery not suffiecient enough power supply?
Very likely. Those 9v batteries are an invention of the devil, good only for very low power devices like smoke detectors and that is about it. It has been said that the reason why Tandy went out of business was that all their stuff used 9v, and their real business was selling 9v batteries to suckers - who eventually woke up to the scam.
Your situation is not helped by the ethernet shield being a bit of a power hog.
I don't know what the best solution is for battery power, it obviously depends on the duty required. I imagine 7.2v of AA NiMH 1800 mAH would be a good and obvious place to start, as they can provide a good slug of power to prove you are going in the right direction.
Naughty Batteries! ok i think i shall try your suggestion with the 7.2v batteries. Can i hook up the batteries straight to the arduino?
Can i hook up the batteries straight to the arduino?
Use standard coax socket. 7.2v still needs to go through the regulator.
is coax socket the same thing as a barrel jack?
Yes - barrel by name, coaxial by nature.