"I received mine today, and it's DOA. I spent hours testing with different microcontrollers (Arduino Pro Micro, ESP8266/Wemos D1 Mini, ESP32), different test sketches, and probing with an oscilloscope.

I finally identified the problem: the module was assembled incorrectly. Since these are probably populated and soldered by machines, I assume the entire production batch is bad. The MAX3421E chip, the heart of this board, is installed 90 degrees clockwise from how it should be oriented. Look at the indexing circle and the text on the chip. The indexing circle SHOULD be closest to the "... v2.0" silk screened text, and the top of "MAX" SHOULD be closest to the USB port. I checked photos from other vendors/manufacturers, and they all have the chip oriented the same way as the Amazon product photo.

If you order one, check the chip alignment first, and then start with the "board_qc" sketch from the examples library to do some basic quality control tests. This should save you some frustration if you also receive a bad module."