So far the state of the project:
Finished / pros:
-Cheap and use very few parts
-Rechargeable, the LIC works really nice and it recharges quickly, also no dropping.
-The microcontroller manages the charging so no need to add a voltage regulator.
-It can be flashed with the usb cable, not standard though, UPDI needs to be feed intro the D+ signal of USB with a flashing solution like serial to UPDI, I know it isn't standard but it is very convenient and it works really well.
-Now charging works ok using a mosfet controlled by timer A .
-Sleep is implemented.
-Whatchdog is implemented to wake up from sleep every 4 sec. checks if device is charging and if the voltage is below 3.8v and above 2.2v to protect the LIC.
(also resets if hung)
To do / cons:
- Although using the usb to feed the UPDI signal is practical, I don't know if it would damage a computer if it is connected to it, it shouldn't since the UPDI is pulled up with a 30k resistor but still a concern.
In case of connecting it directly to USB by mistake, using the UPDI adapter to send the signal is ok.
I tested once and nothing happened but doing it repeatedly is another story.
- 4k of flash is a small amount, in my case I have to chop content of the game, someone with more knowledge I am sure can fit more, considering in using a bigger micro????.
WORK IN PROGRESS!