a little device with two serial ports and a USB port and a PS/2 connector. On one end, you'd connect it to a standard vt100 console port of some UN*X machine, and at the other end you'd connect either a serial display or a USB display and optionally a keyboard. The little thing would just need to speak vt100 on one port, and implement some braille display protocols for the other end.
Sounds like something like this could be done with a "gumstix" computer. You can learn more at their site, www.gumstix.com where they offer a variety of miniature SBCs (single-board computers). By "miniature", it looks like they're about the size of a large-ish candy-bar...maybe a big (not king-sized) Snickers, PayDay or Baby Ruth. 83mm x 36mm x 15mm according to one spec-sheet I read for the encased model.
They all run Linux. The lowest end model (running an XScale processor at 200mhz) runs around $99 and has an optional $20 daughterboard to add 2x serial and USB. It looks like it may do just what you want.
I've not toyed with them, but I keep hearing good things about them. They have other daughterboard modules with 10baseT, WiFi, or BlueTooth for networking, or audio connectors if desired if that was your sort of game too. Two Linux Journal reviews of different modles can be found at
http://www.linuxjournal.com/article/7652 http://www.linuxjournal.com/article/8268
I don't know how hard it would be to get brltty or other such tools running on such a critter, but IIRC, you'd be the guy with the know-how on that front (grins).
It's not battery powered, but runs 5v, of an included AC-to-DC power supply. However, a little technochicanery might be able to wire up a small laptop, handheld, or cell-phone battery to provide it with juice.
Just a little something that happened to come across my plate at the same time you mentioned the prospect of doing something like this.
-tim
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