Now that Bluetooth modules are dirt cheap, I'm wondering if I could make a pair of wirelessly connected objects that would act as a "virtual USB cable". One would have a pig tail with a USB Male plug (USB-host side), and the other would have a USB-device end on its pig tail. The goal would be for them to be able to wirelessly act like a wired USB cable, but wireless.
Requirements are simple:
1) Commodity hardware. If the cheap Bluetooth modules, plus a cheap MCU or two can do it, it's fair game. I can code and design circuits, but this project doesn't warrant me designing PCBs from scratch and coding protocols from scratch.
2) Does NOT need to support high speeds or charging port or anything fancy. If it can do USB 1.0 reliably, great. Primary usage would be for either USB printers or programming MCUs (Arduino, Launchpad, etc.) Neither of which need huge bandwidth.
If this is doable, what would the basic data chain look like? (Example: Host-side would be a generic PC USB dongle (just needs to support _____ protocol), and it would communicate via Bluetooth Serial (or other protocol) to the client that would be a generic Bluetooth module hooked to a ATMega32u4 board configured to use _______ protocol on it's USB out.)
I could swear I've seen online projects of guys doing this, but now that I'm interested in attempting it, I can't seem to find a similar project online to get a basic idea of how it would be done. If anyone knew of one, and had a link, I'd appreciate it.
Just as valid of an answer would be to point out why something like this won't work. (Obviously, such devices aren't being sold on E-bay en-masse, so their could be a real answer why USB signals can't be bridged across a wireless link due to latency or some-such.)
Best Answer
Yes, this is possible.
As you pointed out, you could implement the interface to the USB host using a USB to TTL UART interface. You would still need a microcontroller in-between to set up the pairing etc. with the other Bluetooth device. So you can't just connect the UART directly to the TX/RX leads of the Bluetooth module. Because of the serial interface, you may be limited to as low as 115,200 bps, certainly no higher than 1 Mbps, which is not even as fast as the slower USB 1.1 rate of 1.5 Mbps.
However on the slave side, you will need to implement a USB host to talk to the slave USB interface. This is not trivial. There are quite a few chips that implement a hardware USB slave interface, but far fewer that implement a hardware USB host interface. On top of that, you will have to implement a USB stack. If you want to be able to handle connections to USB hubs, its even more difficult. Depending on the microcontroller you pick, you might be able to get a library to help with this, but plan on spending a lot of time getting it working.