My pleasure, @reeddavid! I’m excited that you might find a use for it. Just a quick note: you may need an external power source for the RPi if you’re switching between devices frequently.

One popular request I’ve received is for certain RPi models (those with multiple USB ports as host) to act as a KVM, allowing them to serve as a USB host for multiple PCs simultaneously with easy switching—perhaps through shortcuts or physical buttons on the RPi. I’ll need to give it more thought, but it seems feasible with minimal changes. I already have some ideas for better state management for the devices!

many Bluetooth USB dongles have NVRAM, you can write the link key for a device (eg the keyboard or mouse) into the NVRAM and then when connecting, the dongle doesn't ask the Host computer for the key. I have used this to dual boot with a Bluetooth keyboard and mouse in the past.

I think the technique would be: pair in machine A (A has a link key). Then, pair again in machine B with the same dongle. Write that key into NVRAM, and machine A considers the device paired but it never gets asked for the key so just works if you plug the dongle into either machine. I don't know how the monitor thing works, does it act as a USB hub? I guess you can just leave the Bluetooth dongle plugged in there..

Fun & cursed fact, the ArchWiki has a rather long section on dual boot pairing. Pair in Windows or Mac then painstakingly extract various bits of pairing info from the OS and toss it into Linux, so you can dual-boot & keep the pairing. https://wiki.archlinux.org/title/Bluetooth#Dual_boot_pairing

I've always wondered how feasible it would be to copy Bluetooth pairing information. This particular series of hacks seems to rest at least somewhat on it being the same Bluetooth host adapter. (But maybe the host side can spoof, trade IDs with the other device?)

Ideally I'd love to centrally and dynically manage what devices of mine are paired with what system... I think that might be technically feasible, as long as I'm not trying to pair multiple things with a single bt adapter.

I've had many BT mouse and keyboards which supported multiple pairing profiles on the device. When I want to switch the device I just press a button on the mouse or keyboard and it's connected almost instantly.

My current keyboard:

https://www.logitech.com/en-us/products/keyboards/mx-mechani...

I had a similar problem but dual booting windows/linux. Though I managed to share the link keys with some registry hacks in the end.

https://gist.github.com/madkoding/f3cfd3742546d5c99131fd19ca...

All of this is being insanely overcomplicated.

Throwing more complexity at a simple problem might be "fun" from a nerd's POV, and, TBH, building this USB device sounds fun. But entirely unneeded while introducing more points of failure.

A simple solution to your problem:

1. Get a monitor with a built-in USB hub (nearly all of them?). Consider getting a USB-C monitor to reduce the number of cables to 1.

2. Don't use Bluetooth (for a keyboard, for multiple reasons, like needing the keyboard available in early boot). Get a keyboard/mouse with an external USB dongle like Logitech's Unify or Bolt, Corsair's SLIPSTREAM, or any of the other billion options that exist.

3. Plug keyboard/mouse into monitor, plug random computers into monitor. Bam. Unified mouse and keyboard without any pairing.

Thank you for the kind words, I'm glad you're finding it interesting! ^^

> could we do BT -> Internet -> BT

Quite probably, though there might be protocol latency issues that you need to be careful of and they might limit the effective range (lookup the “We can't send mail more than 500 miles” tale for a related issue!).

Well, you need a frame converter that sends it to an IP address/DNS server, and on the receiving side something that receives that packet on a specific port and translates it to a BT command.

I would say the most complicated part would be the TCP/IP stack, and binding/publishing your address, but if you are running something with Embedded Linux it is doable :)

Thank you, I'm glad you're finding this inspiring. I've been thinking about some similar ideas that excite me. Would be happy to help as well if you ran into any blockers.

Magic Trackpad 2 and (Mac) Magic Keyboards appear as USB HID devices when connected to a computer via Lightning-to-USB (-A or -C) cable.

One annoyance is that macOS automatically Bluetooth pairs with these devices when connected via USB, overwriting any existing pairing, but this shouldn't matter for purely wired scenarios.

For switching Bluetooth devices more generally, observe that most Bluetooth controllers are USB devices; with a bit of effort — mostly just copy/pasting the device pairing keys across all connected hosts — they can be switched just like any other USB peripheral (YMMV with "intelligent" USB KVM switches that virtualize USB HID device connections).

IME the connection delay is a couple seconds longer than switching wired USB HID devices directly, but entirely reasonable for typical KVM use cases.

Note here that "most Bluetooth controllers are USB devices" even extends to internal Wi-Fi/Bluetooth combo cards, which are commonly M.2 key A or E (= PCIe + USB 2.0 + …), or M.2 key A or E preinstalled on a mostly passive PCIe adapter, with a separate cable connection to a USB port or motherboard USB header used exclusively for Bluetooth.

This turns out to be a surprisingly useful implementation detail: on one of my work desktops, I'm currently virtual USB-switching the Bluetooth controller on an Intel BE200 PCIe card between a Linux host and a Windows VM running on that host, while keeping Wi-Fi connected to the host.

I have a matching hot key set up in each OS to attach/detach the Bluetooth controller from the VM and simultaneously DDC switch the monitor input between the host (iGPU) and guest (PCIe dGPU passthrough), and it works great.

Coincidentally, the Bluetooth devices I'm using in this configuration are a Magic Trackpad 2, a Magic Keyboard, and a Magic Mouse (the mouse was the motivation for using Bluetooth over USB in the first place, as, unlike the other Apple input devices, it's physically impossible to use when connected via USB).

At least older models of Apple Magic Trackpad work over USB just fine. I have one plugged via USB to my monitor, which acts as a KVM.

Have you tried usb? My Magic Trackpad and keyboard work fine without BT on both windows and pop os. Would love a way to actually disable the radios though.

It's not unnecessary complexity if the thing wouldn't get made otherwise, especially for a personal project.

Thank you!

I think that's a fair point about potentially wasted resources, something like Pico would have been and a leaner choice if this was going to be mass-produced. But for me, part of the decision was my comfort level with system programming and what I desired to tinker with and learn along the way and still, it's a very affordable option (around 20 CAD I believe)

Perhaps I'll look into porting it to Pico in future as new challenge and learning experience. Thank you for your sharing your thoughts.

I would think an esp32 with Bluetooth would do wouldn't it?

Right, I think it is doable (an would say even easier/faster) with Raspberry Pico Pi W controller, it has BT and can behave like USB HID device.

a.k.a.

> A delightfully over-engineered solution

Thank you!

Great question. I can see this being fairly easily extendable to other HID devices and even modifying their behaviour slightly (e.g. remapping a key) but audio stack sounds like (no pun intended) a different beast altogether. A buddy of mine had a similar question around connecting his BT gamepad and headset to play PS games on PC so I'll be looking into this more.

If you have a wired connection to the box you should be able to use wake on lan from a phone (this is what I used to do, now homeassistant took over this responsibility).

Oops, I hope you can still return it!

I'm glad you might find this useful, be sure to create an issue on GH in case you run into any and I'll try my best to help :)

Actually, I meant to say Pi Zero 2 W as well. But basically, any device that supports USB OTG

You can just buy a very cheap module which does this directly, commonly called HC-06 or HC-05

e.g. https://www.aliexpress.com/item/33010159305.html?spm=a2g0o.p...

You can, of course, DIY something easily enough but you can also purchase devices like this off the shelf. Needing to make legacy RS232 devices wirelessly available is a common problem in industry. Search for "wireless RS232 gateway" and you should be able to find a ton of stuff.

If you still want to DIY, an ESP32 (BLE and Wi-Fi capable microcontroller) board, and an RS232 to logic-level breakout board should be all you need. Again, I'm sure if you search, you'll find existing projects doing exactly this.

If it's not actually at RS232 voltage levels and Classic Bluetooth is enough, then something like this will work just fine: https://www.amazon.com/Wireless-Bluetooth-Transceiver-Integr...

You may find esp-link interesting: https://github.com/jeelabs/esp-link I've built a WiFi<->RS232 bridge using the firmware, ESP8266 and a UART<->RS232 converter module. All hardware is very cheap.

Oh interesting, I can see how something like that would be useful for myself as well. I think you just gave me some good ideas for future projects as I have a few ideas around using Bluetooth in React Native apps and potentially amalgamating them with Single-board computers. Thank you!

For Android there is an app that does this. https://play.google.com/store/apps/details?id=io.appground.b...

Blackberries could do that, I think it was called Blackberry Connect or something like that. I used to use my Bold as a keyboard for my laptop when it was parked next to the projector.

I would be interested to know too, be sure to let me know how it goes!

My workplace doesn't even allow us to plug in (unapproved?) USB devices, so even this workaround likely wouldn't fly here.

The reasoning I’ve heard is that Bluetooth traffic is easily snoopable without physical access to the device. Someone could potentially steal password keystrokes while sitting outside the office building, on the other side of a window with the shades drawn, whereas with USB you still need to get past the physical security and be at their desk.

In my company USB port is generally disabled for storage and docks, but HID devices, like keyboards, work

Yes, that's weird. USB is a worse attack vector than Bluetooth.

I know, it seemed to me like a pretty arbitrary policy as well, but what can you do other than turning limitations into opportunities? ¯\_(ツ)_/¯

Any SbC with OTG support should work, so both Zero W and Zero 2 W should be compatible (I tested it with RPi Zero 2 W—I will update the docs).

https://www.raspberrypi.com/products/raspberry-pi-zero-2-w/ https://www.raspberrypi.com/products/raspberry-pi-zero-w/

I can't find definitive information for RPi 4 though, I see some references to using it online but the spec here does not seem to mention USB host or OTG

https://www.raspberrypi.com/products/raspberry-pi-4-model-b/...

Audio support would be awesome. I would love to be able to use my AirPods and other Bluetooth headphones on gaming consoles

Not at the moment, I might look into it as I've received the request a few times now. So stay tuned! :)

Thank you so much!

Not quite, if your PC has a policy that disables Bluetooth, a BT dongle would not work either.

That’s where this relay comes in—it bridges Bluetooth to USB, so you can still use your devices.

IT departments that are too restrictive will soon find that people have a parallel world executing in Excel sheets and using some external messaging app to keep the company operations running despite IT efforts to ensure it doesn't - I mean to ensure it is "secure"...

Thank you for sharing your thoughts, I had thought about this as well but came to the conclusion that from the company's perspective, this is no different than connecting a random keyboard bought from Amazon, what do you think?

Another thought around this is that I don't even think there's anything intrinsically insecure about BT as an attack vector but most likely some old policy based on security issues that existed in the early days of Bluetooth. Or at least I don't know of any, but I'm no expert in this so I would love to hear other people's insights here.

No, it's just a USB device at that point. Unless they are against USB mice and keyboards, it's fine.

The clever IT department will put hot glue in all USB ports.

What could those do special?