Mystery USB device on Ebay

[TonyRPH]

I bought this device purely out of interest - it's labelled as a "USB to USB digital interface".

I opened it up and there are two chips on board, STM32F401 micros.

I plugged it into a disposable Linux USB and it doesn't show up as anything - however I found a button on the back side of the board, and that puts the device in a programming mode (DFU mode), at which point it's visible in the USB stack.

Now the question is; why two STM chips and what can I do with it?

Link to the device in question

Obligatory picture! (there is a USB socket for output and a trailing cable for input).

[fat80b]

TonyRPH said:

I bought this device purely out of interest - it's labelled as a "USB to USB digital interface".

I opened it up and there are two chips on board, STM32F401 micros.

I plugged it into a disposable Linux USB and it doesn't show up as anything - however I found a button on the back side of the board, and that puts the device in a programming mode (DFU mode), at which point it's visible in the USB stack.

Now the question is; why two STM chips and what can I do with it?

I'd presume that the ST chips are connected to each other and there are two of them because each one has one USB device interface and that's the easiest way to connect to two USB masters at the same time.

I would assume that the behaviour / purpose will be custom as they are generic programmable microcontrollers and you could easily implement almost anything you like over USB (most likely bulk endpoints with custom commands / behaviours).

If it was something less custom / more standard in terms of operation, then you could imagine using this hardware to connect two computers together, both ST chips enumerating as a mass storage device and enabling you to drag and drop files between them (perhaps).

Or maybe enumerating as a pair of USB audio devices (mic on one, speaker on the other) or something like that?

You should be able to query the USB vid and pid on both sides, and see what endpoints it presents?