Android, Bluetooth.

04. Bluetooth config file.
# cat /data/misc/bluetooth/bt_config.xml

03. Get Bluetooth MAC.
# adb shell settings get secure bluetooth_address
or # settings get secure bluetooth_address
or # service call bluetooth_manager 10  (10 for Android 4, and 12 for Android 5)

02. Get Bluetooth connection via ADB.
# adb shell am start -a android.bluetooth.adapter.action.STATE_CHANGED

01- Turn ON/OFF Bluetooth via ADB.
Turn ON Bluetooth way 1.
step-1
# am start -a android.bluetooth.adapter.action.REQUEST_ENABLE
(but it required user to accept a dialog)

step-2 (dialog pop-up)
# input keyevent 22 & input keyevent 22

step-3
# input keyevent 23

Turn ON Bluetooth way 2.
# service call bluetooth_manager 6
(and no any accept dialog)

Turn OFF Bluetooth.
# service call bluetooth_manager 8

Pi, CLI Audio.

Link reference 1: https://www.raspberrypi.org/documentation/configuration/audio-config.md
Link reference 2: https://www.raspberrypi.org/documentation/usage/audio/

Switch audio output.
# amixer cset numid = 2     (2 is HDMI, 1 is Headphone jack, 0 is automatic by default )

Audio player.
# omxplayer example.mp3
# omxplayer -o hdmi example.mp3     (force output over HDMI)
# omxplayer -o local example.mp3     (force output over headphone jack)

Repeat playback
============
# omxplayer --loop example.mp3

[ Sys Reply ]
Audio codec mp3 channels 1 samplerate 11025 bitspersample 16
Subtitle count: 0, state: off, index: 1, delay: 0
Seek to: 00:00:00
Seek to: 00:00:00
Seek to: 00:00:00

[Ctrl + C] Quit player.

Arduino, RGB sensor TCS34725.

Required library Adafruit_TCS34725.
Turn Off embedded LED, wired TCS34725 of LED pin to Arduino of GND pin.