+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.
+
+
+
+
+