You can use the Bluefruit LE UART friend with any microcontroller with 3 or 5V logic. Here we will demonstrate software serial with an Arduino UNO and hardware serial with an Arduino MEGA. Depending on whether your microcontroller has a hardware or software UART, adjust pins as necessary!

Wiring for Arduino Uno

To connect the Bluefruit LE UART Friend to your Arduino Uno using the default pinout in our sample sketches, connect the pins up as follows:

  • MOD to Pin 12
  • CTS to Pin 11
  • TXO to Pin 10
  • RXI to Pin 9
  • VIN to 5V
  • RTS to Pin 8
  • GND to GND

The wiring diagram below shows how this might look on your system:

All of these pins are 'flexible' and you can change them around as necessary after you get your setup running nicely, but we recommend starting out with our default wiring.

Wiring for an Arduino MEGA

This is the recommended approach on an Arduino MEGA. This should also work for an Arduino Micro, Leonardo, or any other board with a hardware serial port. To connect the Bluefruit LE UART Friend to an Arduino MEGA (Serial1 in this case), use the following pinout and make sure you've selected HW UART as the constructor in your sample sketches (they default to SW Serial):

  • TX1 to RXI
  • RX1 to TXO
  • +5V  to VIN
  • GND to GND
  • Also connect CTS on the Bluefruit LE Module to GND

The HW Serial constructor can be seen below, and should be uncommented in the sample sketches:

/* ...or hardware serial, which does not need the RTS/CTS pins. Uncomment this line */

Not Connecting? Try a Power Cycle

If the example sketch does not appear to connect, like this:

Then double check your wiring and make sure the slide switch is in the CMD position. If that all seems OK, you can also try power cycling the Bluefruit LE UART Friend. Simply remove the 5V wire for a sec and then reconnect it. Then try running the sketch again. Hopefully it'll start responding then.

Wiring for an FTDI Cable

Since the UART Friend is, well, a serial port, you can use an FTDI Friend or cable to quickly connect using any serial console. You won't get MODE or DFU connections, so don't forget to flick the mode switch as necessary if you want to be in a particular mode.

Simply insert an FTDI cable directly into the Bluefruit LE UART Friend header by using the six pins in the middle, being careful to align the power pins up correctly (the red wire to VIN and the black wire to GND):

This guide was first published on May 01, 2015. It was last updated on Mar 08, 2024.

This page (Wiring) was last updated on Mar 08, 2024.

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