+Bug:
+- with Nexus5 keyboard and mouse are very laggy.
+
+Power saving:
+- 8MHz clock
+- When not connected in a few minutes get into deep sleep to save battery life
+- CTS is needed for waking up from deep sleep? How deep sleep is activated?
+- firmware controlled 3.3V DC converter to switch on/off BT module
+- sleep MCU and BT module(keyboard is not used)
+- deep sleep MCU and BT module(keyboard is not used for long time)
+- deep sleep MCU and turn off BT module(keyboard is not used and not connected)
+- Battery ADC; switching, high resistance
+ - switching gnd end of divider with PF4
+ - high resistor 100K/1M?
+ capacitor 10nF
+ http://www.eevblog.com/forum/beginners/measuring-battery-voltage-without-consuming-current/
+
+Improving:
+- BT LED; connecting, linked, sleeping, deep sleeping
+- Battry LED; blink(using timer?)
+- move rn42 to protocol directory when it becomes reusable stack
+- LUFA sendchar should be buffered and serial_uart.c buffur size is too large(256).
+- ADC resolution
+ AVR120
+ AVR32138
+
+Testing:
+- Factroy reset doesn't work; need to **test again** 10K pull-up is too high?
+- Lipo voltage ADC value is not stabilized
+- DCDC converter: squeaky inducter; try other inductors
+
+- Keymap layer bug: during space is pressed(mousekey) press Fn(HHKB) then release space before Fn, in result HHKB layer is locked(toggled) unintentionally.
+
+
+Done:
+- low battery alert(solid light) 09/04
+
+
+Power routing
+-------------
+Current:
+(USB) +---(Lipo)
+ | | |
+ | | +------+ DPDT
+ | | |Switch/-----------------------+
+ | | +------+ |
+ | +-------+ | |
+ +-|Charger| | |
+ | +-------+ | +---+ |
+ | | |MCU| |
+ | | +---+ |
+ | | | |
+ | | | |
++--------------+ +-----+ +------+ +---/--+ +-----+
+|Power Selector|--|DC 5V|--|DC3.3V|---|Switch|----|RN-42|
++--------------+ +-----+ +------+ +------+ +-----+
+USB Power is boosted unnecessarily, not harmful?
+
+Idea 1:
+(USB) +---(Lipo)
+ | | |
+ | | +------+ DPDT
+ | | |Switch/----------+
+ | | +------+ |
+ | +-------+ | |
+ +-|Charger| | |
+ | +-------+ | +---+ |
+ | +-----+ |MCU| |
+ | |DC 5V| +---+ |
+ | +-----+ | |
+ | | | |
++--------------+ | +---/--+ +------+ +-----+
+|Power Selector|-----+---|Switch|----|DC3.3V|-----|RN-42|
++--------------+ +------+ +------+ +-----+
+To enable BT when USB powered it still needs to turn siwtch on, Lipo consumes quinscent current at 5V converter in vain.(Not good)
+
+Idea 2:
+(USB) +---(Lipo)
+ | | |
+ | | +------+
+ | | |Switch|
+ | | +------+
+ | +-------+ |
+ +-|Charger| |
+ | +-------+ | +---+
+ | +-----+ |MCU|----+ Controlled by firmware
+ | |DC 5V| +---+ | On: Lipo powered
+ | +-----+ | | Off: USB powered
+ | | | |enable
++--------------+ | +------+ +-----+
+|Power Selector|-----+---|DC3.3V|-----|RN-42|
++--------------+ +------+ +-----+
+MCU can controlled power of RN-42 without hardware switch.
+When USB powered and switch is on Lipo consumes quinscent current at 5V converter in vain.(Not good)
+
+Idea 3:
+(USB) +---(Lipo)
+ | | |
+ | | +------+
+ | | |Switch|SPST(or without)
+ | | +------+
+ | +-------+ |
+ +-|Charger| |
+ | +-------+ | +---+
+ | | |MCU|----+ Controlled by firmware
+ | | +---+ | On: Lipo powered
+ | | | | Off: USB powered
+ | | | |enable
++--------------+ +-----+ +------+ +-----+
+|Power Selector|-|DC 5V|-|DC3.3V|-----|RN-42|
++--------------+ +-----+ +------+ +-----+
+Switch is needed to save Lipo when not used because decent power saving is not available now. If firmware can turn off BT module completely and make MCU deep sleep the switch will be not even needed.
+
+
+
+
+
+DONE:
+- BT_INDICATOR LED turns on wrongly when touching line or pin. -- pull-up enabled on PF6/GPIO2 08/30
+- Lipo charger configuration: fast charge time: USB charger spec? -- used 2kohm
+- use LED of charger to alarm low battery. LED should be powered directly from Lipo? - cancel; powered from VUSB
+- Use RTS in serial_uart.c to resolve missing chars from help message of RN-42 - done
+- CTS/RTS lines are needed? just connect in loop back if no flow control is needed. - done
+- add IO pin to charger status CHRG; LED control(low) and detect charge status(input HiZ) 07.24
+- LINKED: add trace on PIO2 to PF6 07.24
+- Lipo voltage ADC sensing
+- Lipo charger MCP73831: needs capacitor 4.7uF *2
+- USB connection check - 07.01
+- BT on/off check: whether RX line is pulled up? - checking RTS 07.01
+- USB/BT switching BT is on -> BT, BT is off -> USB - 07.01
+- Under voltage lock out UVLO for protection of Lipo - Lipo has discharge protection at 3.100V 07.01
+- Power saving: HHKB scan, BT radio control - 9h with 850mAh, this is enough 07.01
+- Power selector doesn't work; Q4 MOSFET leaks from Lipo to USB power line. -- use Schottky instead 07/04
+
+
+
+TROUBLE SHOOT
+-------------
+07/16 After fix of voltage dividor on GPIO6, had a trouble that it could not send a char to BT module, though could receive.
+ Found R8 had wrong 1K resistor and changed to 10K, after that it can send to the module again. Not sure how it had sent with the wrong 1K before.
+
+07/18 On Linux, had an USB related trouble; keyobard or console didn't work for some reason. Changing PID cured this problem. Very annoying, took very long time before resolved it.