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I have the following problem/idea:

I have a electronics workbench and a separate PC desk. Now I have a USB HUB on the workbench, but it doesn't properly work, because the USB-cable to the pc is too long. My setup doesnt really allow me to put the PC somewhere else and the USB-hub is already mounted in the closest usable location.

A few days ago I remembered that I have a arduino nano with a hc-05 bluetooth module attached to its hardware serial port. And as both bluetooth and USB are serial connections I was wondering if I couldn't use the arduino sort of as a middle man and connect the arduino via bluetooth to the pc. Then have a software on the pc that registers the arduino as a USB hub with one port and run some code on the arduino that basically makes the arduino act as a USB host (I know that this is possible with the arduino nano) and have it just move data between the USB connection and the bluetooth module.

Im quite sure that all this should be possible. The atmega should even be capable of doing so at or close to maximum USB 2.0 data rates as that is only 12 Mbit/s and it can run at 16 MHz when powered with 5V. Im not quite sure about the maximum data rate for the bluetooth module though, but I can work with a little lower speeds...

The software for the pc could also be relatively straight forward. Something like a virtual USB-port and the software just shifting data from the com-port that is the bluetooth to this virtual USB-port.

So thats the idea. I have some experience in both programming microcontrollers and software for pc.

So what I need is a bit of help with this, as I am not quite sure how to accomplish this.

The parts that I will need the most help with are going to be the programming of the USB host on the arduino and the virtual USB-port on the pc.

The rest should be relatively easy as its basically just shifting data from one register into another.

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    as both bluetooth and USB are serial connections well, yes, they are both serial, but saying they are anything even remotely alike is like saying that an elephant and a bicycle are similar because they both move forwards and backwards. – Majenko Apr 8 at 17:19
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You can't. As simple as that. The mere act of thinking about it belies a desperate lack of understanding about how USB works.

Yes, it's "serial" in that it sends one bit after another, as opposed to multiple bits all together ("parallel"), but it is completely unrelated in any way to the "serial" that the bluetooth module or the Arduino speak ("UART").

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I agree with Majenko. The best way for you is to buy an active USB extension cable, so that you can handle the distance easily (the signal gets refreshed in the cable by active electronics, so that you can use USB over longer distances).

You consider this to be easy, because you haven't dug into the depth of these topics yet. Here are some important information on that:

  • Bluetooth and USB are fundamentally different. The term "serial" outside of the Arduino world is just a term for one bit after another. It doesn't describe any protocol or working principle. Interfaces as SPI and I2C are also serial interfaces, but that doesn't mean, that they work similarly, not even in their topology and also not in their protocol behavior. A bridge between these different interfaces is better described as a translator. And translation is always difficult.

  • Serial in the Arduino world means the UART interface. No similarity to USB or bluetooth.

  • The Bluetooth spec is rather big. There are many types of connection interfaces, that can be build with it. Examples are the UART (Arduino Serial), HID (like a mouse or keyboard on a PC) or audio (like headphones) interfaces. Each connection has it's specific function. The USB spec is even bigger, way bigger to be precise. You would need to understand how bluetooth and USB work at their core for implementing something like that.

  • The HC-05 is a chip for getting an UART interface over bluetooth. To change that, you would need to reprogram it with a new firmware. I doubt, that any firmware, that you can find in the web, would be sufficient for your case. Not generic enough. Also the chips hardware is limited, so you can only get limited resources out of it. Most likely you have the HC-05 on an adaptor board, which has a voltage regulator on it (since the HC-05 is a 3.3V device). You would need to ditch that board and solder the chip itself.

  • The Nano is a bad choice for everything involving USB. The Atmega328p on it, that you program when programming the Arduino, does not have an USB interface. For that the Nano has a second chip, the Atmega32u4, which acts as USB to UART adaptor. You would need to hack it to do anything different than that. Doing it is possible, but you would need to ask yourself, why you are trying to do something so complex with such an incapable board. Also the Nano cannot be an USB host, nor a hub. There is an USB Host shield for the Uno, but that also is limited.

  • Getting anything even remotely near to 12Mbit/s is illusionary. You won't be able to process nearly one bit every clock edge. You already need several clock edges to do very primitive processing (going into an ISR and then moving the data into a different register, as you put it). And the translation between the protocols will not be that easy. You will need much processing power and also quite some RAM and flash (you will certainly need to buffer some data and the program itself will also be very big to implement something like USB). "A little lower speeds" don't cut it there. Even if possible, that would be painstakingly slow in comparison to a real USB hub.

  • Most of the software, that you would need for such a project, is non-existent. Doing something that complex with such crappy hardware is an edge case. So you would need to write your own USB stack software. As mentioned, the USB interface is very complex and if you need to ask this question, you are currently not capable of doing this (and neither am I).

I don't say it is absolutely impossible to implement a bit USB functionality with the Nano. But you won't get a satisfying result, that you really can use, even if you were an absolute expert on microcontrollers and the USB and bluetooth stacks (which you really would need to be for it). That is at maximum a project, that an expert would do just for the grind, not for real results.

You have a real life problem, that you want to solve. Choose the easiest way and buy an active USB extension cable.

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