In the center is the bluetooth radio module. This module does all the heavy lifting of creating the RF connection and sending data back and forth. It's a custom module made for Adafruit and is FCC and CE certified.
There are three LEDs, one red and two blue.
The red Connection LED is used to indicate the state of the bluetooth connection/link. If it is slow-blinking, there is no pairing for the module. If it is fast blinking, it's paired to a computer and the wireless connection is 'live' - the computer has opened a UART connection and is sending/receiving data.
The two blue LEDs are for monitoring the data received & sent. When data is sent from the computer to the module, the TX LED will blink. When data is sent from the module to the paired computer, the RX LED will blink. You can use this to debug your wiring and connection.
The pair button is used to reset the computer pairing for Bluetooth link. If you want to re-pair the module, press the button for 5 seconds, you'll see the red LED fast-blink to indicate its ready for pairing! You can now use your computer to Bluetooth-scan for the EZ-Link device.
There is an on-board regulator that can take 3-16VDC and convert it to 3V to power the RF module. The regulator is also reverse-polarity protected.
Onboard level-shifting circuitry converts any input data signal to be 3V safe, so you can use a 5V microcontroller.