This USB dongle/key type thing is a little unusual - it isn't a BLE adapter that you plug into a computer to add wireless capability. (If you do want something like that, our Bluetooth 4.0 USB Module will do the job nicely.) Instead, this is basically a minimal nRF52840 wireless microcontroller dev board on a stick. You can program it in Arduino or CircuitPython and it's completely standalone. This could be useful for some situations where you want to have a standalone BLE device that communicates with a USB host but without dealing with the operating system's BLE stack.

Each MDBT50Q-RX dongle comes pre-programmed with the TinyUF2 bootloader, which makes loading code onto it very easy (note that only the ones from Adafruit do this, its a special-order item). To enter the bootloader, hold down the dongle's button while inserting into USB. The button can be used in Arduino/CircuitPython as an input. There's also a single blue LED indicator. It's all very simple but we could see situations where perhaps this acts as a beacon, a OS-less BLE interface or bridge, or a compact development board for experimenting with the nRF52840.

The blue LED is connected to P1.13, set that pin to be an output and pull low to turn on the LED

The button is connected to P0.15, set that pin to be an input with an internal pullup - when pressed the pin will go low.

Of course the best way to program these chips is with the Nordic SDK. This chip also has some basic Arduino support, CircuitPython support, and is supported by MyNewt.

Specifications:

• 32-bit ARM Cortex M4F CPU
• Supply: 1.7 V – 5.5 V
• Flexible and configurable 48 GPIO
• Bluetooth 5, IEEE 802.15.4, 2.4 GHz transceiver
• -95 dBm sensitivity in 1 Mbps Bluetooth low energy (BLE) mode
• -103 dBm sensitivity in 125 Kbps BLE mode (long range)
• +8 dBm TX power (down to -20 dBm in 4 dB steps)
• On-air compatible with nRF52, nRF51, nRF24L and nRF24AP Series 
• Programmable output power from +8 dBm to -20 dB
• RSSI (1dB resolution)
• Supported data rates:
• Bluetooth 5: 2 Mbps, 1 Mbps, 500 kbps, 125 kbps
• IEEE 802.15.4-2006: 250 kbps              
• Proprietary 2.4 GHz: 2 Mbps, 1 Mbps
• Advanced on-chip interfaces
• USB 2.0 full speed (12 Mbps) controller
• QSPI 32 MHz interface
• High speed 32 MHz SPI
• Type 2 near field communication (NFC-A) tag with wake-on field‧Programmable peripheral interconnect (PPI)
• EasyDMA automated data transfer without CPU processing on peripherals‧12 bit, 200ksps ADC – 8 configurable channels with programmable gain
• 4 x 4 channel pulse width modulator (PWM)units with EasyDMA
• Audio peripherals : I2S, digital microphone interface (PDM)
• 5 X 32-bit timers with counter mode
• Up to 4 x SPI masters / 3 x SPI slaves with EasyDMA
• Up to 2 x I2C compatible 2-wire masters / slaves
• 2 x UART(CTS/RTS) with EasyDMA
• Quadrature decoder (QDEC)
• 3 x 24-bit real-time counters (RTC)
• Operating Temp: -40°C to +85°C 
• Product Dimensions: 43.0 mm x 18.4 mm x 9.3 mm / 1.7" x 0.7" x 0.4"

Documents:

• Datasheet

Warranty: 30 days

• Warranty will not apply if Product fails or is damaged after delivery to you due to accident, abuse or misuse.

Package Includes:

• 1 x Adafruit 5199 nRF52840 USB Key with TinyUF2 Bootloader - Bluetooth Low Energy - MDBT50Q-RX