Direct / Soft Serial Switch

The most important element on the shield is the software/direct switch. The shield has two modes:

  • Direct serial, where the bluetooth module 'replaces' the onboard USB->Serial chip. Used for reprogramming
  • Software serial, where the Arduino can use any two pins to connect to the bluetooth module, but then it cannot be reprogrammed over bluetooth

For users who want a 'wireless link' that can reprogram the Arduino, use Direct only!

If you want to program over USB and then use Bluetooth to communicate with a computer over a seperate link, use Soft Serial

Extra Breakouts

We broke out some extra pins you may or may not need. If using the shield in Direct mode as just a wireless link, you can do without these pins. But advanced users may find them useful!

  • Conn - this is the connection status pin, it has logic HIGH when there's a bluetooth pairing. Useful if you want to activate something when a connection is established, or stop when the connection breaks
  • 3vo - this is the 3.3V output from the onboard regulator, may be handy if you need an extra 3.3V regulator, 50mA max
  • STX - this is the Software Serial TX pin, used in Soft Serial mode. Connect to any Arduino pin you like (that supports software serial!)
  • SRX - this is the Software Serial RX pin, used in Soft Serial mode. Connect to any Arduino pin you like (that supports software serial!)
  • DSR - this is a pin that you can use for sending a single bit indicator back to the computer on the DSR line. Since we have the DTR pin out for resetting the Arduino, we broke this pin out too. It's not high speed so you cant send data over it, just useful as a signaling pin


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.

Pair Button

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.

Reset Button

The larger reset button is for resetting the Arduino, it does not affect the bluetooth module or pairing

This guide was first published on Sep 03, 2014. It was last updated on Sep 03, 2014.

This page (Pinouts) was last updated on Sep 03, 2014.

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