, lacking a friend to travel the wide world with? When you were a kid, you may have learned about the "buddy" system. Well, this product is kind of like that! It is a board that will watch your QT Py's back and add a USB Host port.

Enhance your microcontroller project with the ability to connect a keyboard, mouse, or disk drive, utilizing widely accessible devices through the use of the Adafruit USB Host BFF for QT Py or Xiao with MAX3421E. Adding USB Host support is made effortless with the Adafruit USB Host BFF, now made even more accessible with TinyUSB's inclusion in the Arduino library as a 'native' host interface.

The Adafruit USB Host BFF for QT Py and Xiao is equipped with the time-tested MAX3421E USB Host chip, utilizing SPI and an IRQ pin for efficient data transmission to a wide range of USB devices. However, due to its reliance on the SPI port for data transfer, the maximum speed is limited to 480Mbps. Nevertheless, this BFF is highly effective for basic HID interfacing and file management with Mass Storage devices. Moreover, it is compatible with popular microcontrollers such as AVR, nRF52, and ESP32, thanks to the versatile USB Host Library.

We personally recommend using the - however, the trade-off is that the chip must have TinyUSB support already, which means it's great for RP2040, ESP32-S2 or S3, nRF52840, SAMD21/51 chips. Make sure your desired QT Py mainboard is supported between the two libraries before purchasing! 

To keep the BFF very compact, we use a micro-B USB "OTG" connector - a full sized USB Type A wouldn't fit! You'll need to use . Unlike our we don't include a 5V power booster, so you will need to power the QT Py BFF over USB or in some other way provide 5V on the 5V power line. However, to make it easier to power-cycle the peripheral, we have wired up a P-FET for switching the 5V host power on and off, you can either short the pin to A0 or you can use the MAX3421E's GPIO pin.

We include some header that you can solder to your QT Py. ; you'll need to trim the headers to 7 pins long.

Remember, you need driver support for the MAX3421E (see above for chips that are known to work). Unless you're using a generic mouse, keyboard, CDC serial, or USB mass storage device, you will also need a USB driver that knows how to talk to the device—and writing a driver is non-trivial.

QT Py or Xiao is not included!