The X-NUCLEO-IDB04A1 is a Bluetooth low energy evaluation board to allow expansion of the STM32 Nucleo boards. It is compatible with the Arduino UNO R3 connector layout, and is designed around BlueNRG, a Bluetooth low energy, low power network coprocessor compliant with BTLE 4.0 and the BALF-NRG-01D3, an ultra miniature balun optimized for ST BlueNRG RF IC, which integrates matching network and harmonics filter. The X-NUCLEO-IDB04A1 interfaces with the STM32 MCU via SPI pin, and the user can change the default SPI clock, the SPI chip select and SPI IRQ by changing one resistor on the evaluation board. The excellent performance of BlueNRG and the best matching between BlueNRG and BALF-NRG-01D3, X-NUCLEO-IDB04A1 passed the RF TEST for Japan Radio Law certification with higher margin above the specification values as well as it is FCC certified (FCC ID: S9NIDB04A1).