I am looking to make my first Arduino project and want the battery to recharge from a solar panel. I want to keep the size of the project to about 10cm x 10cm so want a small solar cell. From what I can find in maplin and on ebay, this will restrict me to about .5v
Will this be enough to charge a 9v battery.
I plan to use a measure the battery level using a voltage divider connected to one of the analogue ports and go into sleep mode until the battery is recharged. How long would this take at .5v
You actually need a little more than 9V to charge a 9V battery.
You also need to look at both the voltage AND the current the solar cell delivers. If your project uses 200mA and the solar cell only delivers 45mA, it can never keep your battery charged.
You need to know both the voltage requirement AND the current draw of your project to do the math needed to find a suitable solar cell.
I don't think it will be possible with the size limits you put on your project.
Why not get a 5V rechargable batery, make solar cells to recharge it, do an over voltage protection, so the voltage on output isnt bigger then 5V.
Then connect that output to usb of arduino ...