I took a look at creating an open source solution in this area last year and in fact someone sent me this page last week. The biggest challenge is spatial. The braille standard places pins very close together.

In modern commercial braille terminals, generally a large assembly is offset from the braille block in order to support it. However, this is not feasible if you want to have a dense array of braille blocks. The primary reason for the bulky designs is that they rely upon piezo-electric crystals which move only a small amount and thus require long levers to actuate the required length. Such a mechanical configuration limits you to two lines of text close together at a maximum.

Another category of solution explored is wheel based solutions, a well established category which fail predominantly on density. Specifically, if you cannot place two lines of text very close together vertically then you are going to have problems providing a significant amount of information at once, because you are either going to have 1-2 very long lines or lines will be so far apart as to create an enormous matrix with reach issues. They are also sub-par on mechanical complexity, aggregate weight, refresh speed, and assembly cost due to part count.

Two alternatives are pneumatic actuation and electromagnetic actuation. The problem with both is that there is no standard solution suitable for small size / high spatial density required, but perhaps one may be developed. https://youtu.be/k1inMrAZ_Eo?t=45 is an example of an actuator created within a relatively small size which would be potentially inexpensive to deploy. Ultimately, data comes electronically so pneumatics may be seen as an expensive and complicated middle-ground offering lower weight as its primary benefit but probably sub-ideal as a primary focus of research due to additional cost and complexity.

My analysis therefore concluded that the future of braille displays lies in on-PCB coils for micro-actuation to reduce cost, weight, and part count while increasing density. This approach was inspired by Carl Bugeja's videos. Since August 2023 I have a working prototype of sorts using commercially available dowel pins and multiple PCBs stacked in a vertical structure. The initial prototypes of this onboard electromagnetic coil based actuation system showed great promise but remain to be validated. Chief concerns are torque and a locking solution, the latter being important for reducing power consumption, though fallback strategies exist (eg. hand tracking or 'presence detection'). I am currently focused on other areas but would like to return to this in due course. I would be happy to open source my work (BOM, KiCAD, OpenSCAD, notes) if others are interested to take it forward.

The current prototype is as follows.

∩ ∩ ∩ ∩
==∩==∩==∩==∩==∩==∩== PCB 1 ==‖==‖==∩==‖==‖==∩==
‖ ‖ ‖ ‖ ‖ ‖ ‖ M ‖ M ‖ ‖
‖ M ‖ M ‖ M ‖ ~ ‖ ~ ‖ M
==‖==C==‖==C==‖==C== PCB 2 ==‖==C==‖==C==‖==C==
‖ ‖ ‖ M ‖ M
M M M ~ M ~
==C=====C=====C===== PCB 3 ==C=====C=====C=====

Position at rest. Ejected position.

PCB 1 functions as a cheap precision guide for the pins.

PCBs 2+3 function as coil bases for the pin actuation. Two are required because the required coil density cannot be achieved with only one PCB. (This necessarily means half the pins are longer and half the pins are shorter.)

M is a small circular magnet, glued to the base of the pin.

C is an on-pcb coil at close to maximum density. When C is energised, M ejects with great force, but because M's diameter is greater than that of the pin's PCB hole, the pin-magnet subassembly stops its vertical travel at the predetermined position.

~ is an active coil field.

Benefits of the design: cheap, uses commercially available components, low weight, achieves required density.

Challenges remaining: Energy consumption, simple cheap control plane to maintain density, locking mechanism (non-energised mechanism for maintaining raised state), manufacturing process development (automation required for cost-effective output due to large number of pins).

References: http://libgen.rs/scimag/?q=braille+display

Other open source attempted solutions:

(1) Electrotactile display. https://github.com/tanjeffreyz/electrotactile-braille-displa... https://patch.com/california/dublin/dublin-high-student-crea... (Upsides: No moving parts. / Downsides: Apparent calibration issues. / Status: Apparently abandoned.)

(2) MOLBED https://hackaday.io/project/27126-molbed-2-modular-low-cost-... (Upsides: Functional. / Downsides: Extremely tedious assembly. / Status: Apparently abandoned.)

(3) Slider https://www.youtube.com/watch?v=rTzhWKBfiuk (Upsides: Viable alternative to piezo-electric crystals. / Downsides: Takes too much space on the other axis, so unsuitable for multi-line (page-style) braille terminals. Still substantial mechanical complexity. / Status: Apparently abandoned.)

(4) Ultrabraille https://ultrabraille.blogspot.com/ (Upsides: Multiplexed multi-user concept, like Unix timesharing. / Downsides: Old, relies upon manually wound pin solenoids, apparently does not match braille standard spacing, seemingly never completed as a product after 5 years of research. / Status: Apparently abandoned.)

(5) Flat pneumatic actuators https://www.youtube.com/watch?v=LlxUZABcah0 - shows how to make small collapsible pneumatic actuators from silicone and mould release agent using 3D printed moulds.