There is a family of "Smart TV" remotes available from Chinese sources for US$10-20 that are actually wireless keyboards. They look more or less like a TV remote on one side, but when you flip them over, they're full (more or less) QWERTY keyboards. I say more or less because they may be missing the Fn function keys along with key modifiers like Control and Alt. The intent is that you can type passwords or search box entries or whatever.

Here's a picture of a typical example, which the manufacturer calls an "Air Fly Mouse". It's available with or without a microphone and with or without backlighting. If you plug the dongle into a PC, you will find that the PC recognizes it as a keyboard, and most of the buttons do normal things. By normal, I mean that the keys send the same codes as you would expect if you had a traditional keyboard with those special keys (media control, and so on). That's confirmed by the slender instructions that came with it. Apparently most smart TV-related devices are expecting that. Handy.

One of the things that is pretty cool about these devices is that they have a gyroscopic motion sensor that lets you move an on-screen mouse just by manipulating the remote. I'm not too interested in that, but I tried it out with an Android TV box. It worked surprisingly well. You have to turn the mouse on/off because it uses more power when the gyros are active. With the gyros off, the MCU is probably sleeping and only wakes up when a button is pushed.

I wondered if I could use this directly or reprogram one for my own purposes. So, after I got one, I almost immediately took it apart. It has no branding or FCCid on the outside. The circuit board was marked with "TYX-MX3v1.6 20190401 2019.6.6". That led me the the web site of Shenzhen TYX Technology Co., Ltd. I was not too surprised to see that the board had pads for a microphone and a dozen or so LEDs for backlight (I bought the cheapest model, and it doesn't provide either). Even though it's not marked anywhere that I could find, I was able to find by searching around that a very similar device has FCCid 2AF3EMX3-V, which in turn leads to a user manual of sorts via fcc.gov (or the slightly more accessible fccid.io mirror site). The user manual describes itself as a requirements document. It's from 2015, so not an exact match for the current devices, but it's probably close.

There are only two chips on the board. A pretty small chip has the marking "ISA 36FA 349". That didn't lead me to anything, and I'm not actually sure it's a chip. It could be some kind of discrete component related to the radio or power conditioning or something, and it just happens to look like a tiny chip. The other chip, of a decent size, was marked "BEKEN BK2535 DH8401S". That led me to this BK2535 product overview. It's an SoC with an 8051-compatible MCU and 32k of flash. That it has flash is pretty promising, but the detailed datasheet and any information about interfacing to the chip is not publicly available.  The Beken company keeps them confidential. In the 21st century, I could probably find the technical docs somewhere with enough diligent scouting around, but I don't want to spend that energy and ethical karma.

Even without the effort of figuring it and out and reflashing it, I might still be able to use one of these remotes for this project because some of the keycodes that it can send are off the beaten path, like Fn keys that are F13 or above. The batteries would last forever, and the device has a nice manufactured look (though a slightly flimsy manufactured feel). The buttons are the typical silicone mat with plungers that push on tiny foil switches. I would still have to remember which buttons did the things I wanted, and I'd have to avoid accidentally pushing any buttons that did other things. So, interesting but not ideal for this use.