# Loopback, again

After pairing your computer to the Bluetooth module, your OS should have created a device file / COM
port for you. On Linux, it should be `/dev/rfcomm*`; on mac, it should be `/dev/cu.*`; and on
Windows, it should be a new COM port.

We can now test the Bluetooth module with minicom/PuTTY. Because this module doesn't have LED
indicators for the transmission and reception events like the serial module did, we'll test the
module using a loopback connection:

<p align="center">
<img height=640 title="F3 <-> Bluetooth connection (loopback)" src="../assets/f3-bluetooth-loopback.png">
</p>

Just connect the module's TXD pin to its RXD pin using a F/F wire.

Now, connect to the device using `minicom`/`PuTTY`:

``` console
$ minicom -D /dev/rfcomm0
```

Upon connecting, the blinking pattern of the Bluetooth module should change to: long pause then
blink twice quickly.

Typing inside minicom/PuTTY terminal should echo back what you type.
