Hav'ent really looked into it yet, but I think that it could be a cool idea for a project.
My Nano will be dealing with a PIR some LED strings and an "Low Batt" alarm.
I think that it could do this aswell.
Any thougts or ideas or just stuff that I should think about before ordering a little more of everything?
Pady:
Any thougts or ideas or just stuff that I should think about before ordering a little more of everything?
I think you should research what a Ni-MH charger needs to do, and then decide whether you can make one, and then work out what additional resources you need to make it.
I think you should research what a Ni-MH charger needs to do, and then decide whether you can make one, and then work out what additional resources you need to make it.
Thanks PeterH
Do you know??
I'm pretty sure that it need to charge the batteries, or?
But I think that it needs to measure the voltage at the batteries and then cut off the power, measuring again and chopping up the supply so that it won't get overcharged.
I also think that it needs to charge the batteries at a rate compared the the size of the batteries.
Am I getting in the right direction?
Sometimes there are people that have seen a module that do "just that" or a very easy way to fix a problem, instead of buying every small piece and solder it together.
The rate of charge is typically "1C" or less. That means it should be charged at a rate that would give it a full charge in an hour. E.g. a 2000mah battery would be charged at 2000ma. It's always better to charge more slowly if you have the time.
A good way to learn how chargers work is to poke around a components retailer and dig up datasheets for battery charger chips. The datasheet for the BQ2003, for example, has a complete flowchart explaining its technique.
Lots of very helpful info at BatteryUniversity.com
BatteryUniversity.com:
The NDV (negative delta voltage) in a NiMH charger must respond to a voltage drop of 5mV per cell. To assure reliable charging, NiMH chargers must include electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. Modern chargers achieve this by combining NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm. These “or-gates” utilize whatever comes first depending on battery condition.
Pady:
Do you know??
I think you probably need to apply a constant current and look for a peak voltage across the battery to indicate that it is fully charged, but you may need timeouts, overcurrent protection, sanity check on voltage rate-of-change etc to deal with faulty batteries or circuit faults. This is what you need to find out. This knowledge lets you break your original requirement 'charge the battery' into a set of lower level requirements. Keep breaking the requirements down until you know exactly how you're going to do everything. This will give you a shopping list of software algorithms and hardware components that you will need to implement your project. Then you can look for sources for the things you need that you don't already have.
Ending up by buying an intelligent charger on ebay for 15 bucks, easier and faster 
for now i'll settle and maybe look into the DIY charger some other time.