connecting a rotary encoder to a tablet through bluetooth

Hi - sorry for the delay - I was at a conference most of last week so didn't get a chance to catch up on the forum.

For BLE HID you just need one of the Bluetooth Espruino devices - the most pico-like is the MDBT42Q breakout as you suggest.

Then all you need is the code at https://www.espruino.com/BLE+Keyboard

if the device (the breakout) is detected as an hid bluetooth by the os, the html page doesn't have to detect an hid!? it's a keypress detected, no more.

Exactly yes, once programmed the OS just thinks it's a bluetooth keyboard - no drivers or special code needed.

@Gordon there is only one unpinned pico board in stock in the shop! really?

Yes - we're running low on stock. I can't make any more at the moment because the chips are still not easily available. For example: https://octopart.com/search?q=stm32f401c­du6&specs=1

The cheapest one in stock there is $25 - more than I am currently selling the Pico for!