Feedback on moving electromagnetic actuator for braille display - Page 1
Forum section: electronics / projects

author: Zain
author_rank: Newbie
timestamp: July 07, 2025, 07:52:00 pm
content: Hi everyone,I'm not an engineer or engineering student, just someone trying to design a low-cost, multi-line refreshable Braille display for a competition. I have no formal engineering training, so I’ve been learning everything as I go.Recently, I discovered this amazing Hackaday project (https://hackaday.io/project/191181-electromechanical-refreshable-braille-module/details#header) that uses small bistable cams containing embedded magnets to control Braille pins. A brief magnetic pulse flips each pin into position, and it remains locked without additional power. However, their design requires one electromagnet per pin. Although they had only prototyped one cell, if scaled to a whole tablet, this could total hundreds of electromagnets. This feels complicated and expensive.My idea was to use just one electromagnet per row of Braille pins, mounted on a rail or sliding mechanism, which travels horizontally under the entire row. This electromagnet briefly activates beneath each pin, flipping the cam into the correct position. Because the cams are bistable, the pins remain set after the electromagnet moves away. This approach should greatly reduce the number of electromagnets needed. To clarify, the device itself will have 60 cells, 30 cells per row, with 2 rows.I attached a diagram which shows a simplified side view of the concept. At the top, you see vertical Braille pins, each controlled by a bistable cam with embedded magnets. At the bottom, a single electromagnet sits on a moving rail or belt. This electromagnet travels horizontally under the row of pins (shown as the path labeled "mechanism"). As the electromagnet moves, it provides a magnetic pulse at each pin location, flipping the cam to raise or lower the pin.Questions I'd appreciate help with:Does this approach seem mechanically feasible?What's a simple and accurate way to move the electromagnet beneath the pins?Is changing to one sliding electromagnet a meaningful simplification, or am I complicating things in a different way?Are there any obvious issues or challenges with this design?Any feedback, suggestions, or constructive criticism would be greatly appreciated, I'm here to learn. Thanks very much!

author: antenna
author_rank: Frequent Contributor
timestamp: July 07, 2025, 08:12:23 pm
content: What if each braille pin had an elbow joint like a piston connecting rod with limited travel to one side such that a matrix of nitinol shape memory wires could pull the connecting rod straight, and then another set of nitinol wires to move them to the unlocked position before the next batch of data is written. If each pin had a spring that added downward pressure (just like a finger pressing down), the connecting rod geometry would hold the pin in the locked or unlocked position without current.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 07, 2025, 08:49:39 pm
content: It is not clear to me how your magnets work. You drew something square and something round in your "cam and magnet", but apart from that it's not very clear. I guess it works with either an overcenter, or something similar to flip dots.The magnet could be moved over some rails with a timing belt and a stepper motor, but the good old method where the user moves the magnet may be a better option.Another idea: A lot of electromagnets sounds complicated / expensive, but electromagnets can be embedded into a PCB. See for example the project below:https://hackaday.io/project/158017-linear-pcb-motor

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 08, 2025, 12:42:32 am
content: Quote from: Zain on July 07, 2025, 07:52:00 pmIf each small piece can work as you hope, maybe.Quote from: Zain on July 07, 2025, 07:52:00 pmA Linear Stepper Motor (lead screw) would manage that - couple of exampleshttps://www.aliexpress.com/item/1005006412866689.htmlhttps://www.aliexpress.com/item/1005008418866803.htmlhttps://www.aliexpress.com/item/1005009263622653.htmlYou would likely need multiple actuator heads, as such a linear drive only manages one axis, for braille you need x3 or 2 x 3That's easy to manage, as they are a known offset, and you can update all 3 or 6 rows in one pass.Quote from: Zain on July 07, 2025, 07:52:00 pmIt will have a finite update speed, but someone reading is not going to be super fast.Quote from: Zain on July 07, 2025, 07:52:00 pmGetting the cam's to be reliable looks like a real challenge.Other ideas:You can get compact magnentshttps://www.aliexpress.com/item/1005009140440032.htmlIf you can chain a 1.5mm diameter and 2mm diameter, you can hold that captive between 2 metal plates with a lubricant plastic spacer with 2mm clearance holes.That gives you a bistable latching pin array, with travel of ~ 1mm, without needing many complex cams.Adjust the metal plate thickness/ magnetic hold to be enough to resist a user's reading finger pressure.To actuate that, you need a simple push and pull scheme.Upwards against gravity can be a non magnetic push finger.Pull down via electro magnet would be likely impractical, but I'm guessing a moving longest thin magnet, (1.5mm x 10mm?) might manage a pop-up-pull-down-probe. Easy to check.You do not need much movement, ballpark 2mm would be ok? so perhaps a small linear motor along the lines of:https://www.aliexpress.com/item/1005005023483602.htmlThe challenge then is how quickly can this updateTo improve speed, you could only move changed pegs, and careful spacing should allow multiple pins to update per pause in long linear motor.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 08, 2025, 12:59:36 am
content: Historically, I'd recommend reading about Dr Linvill's Optacon. Sure, it's 50+ years old but I think the research he did into what works for touch and the actuators themselves may be interesting.

author: spostma
author_rank: Regular Contributor
timestamp: July 08, 2025, 02:51:43 pm
content: An odd idea; would a 'heat pixel braille' be usable for you?I would use a matrix of 0603 or 0402 smd resistors (or tiny zener diodes) that heat up in a braille pattern,and make the surface level using epoxy filler.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 08, 2025, 11:56:04 pm
content: Quote from: Zain on July 07, 2025, 07:52:00 pmThinking some more on this..You are correct, most is 3D printed but the tiny coils here are custom hand wound, and that is very labour intensive and costly.What about a hybrid - keep most of the 3D printing and cam concept, which they seem to have working, and focus on reducing the labour of many coils.Standard bobbin inductors are available, smallest standard size looks to be 5mm, sub 10c each.5mm is likely too large to flip one magnet and not affect adjacent ones, tho it is well worth experimenting on that.More predictable would be a 5mm coil with a magnet focus cap of a small iron screw or rivet, that focuses the magnetic field to < 2.5mmThis coil+cap could be glued or heat-shrunk.This is all too large to be fixed in place, but your moving carriage idea solves that.See image below for the coil + iron cap combination.Lowest number of these would be 3, staggered to fit the finer braille pin pitch, and aligned so all 3 can do useful work.Because these are now standard low-cost parts, you can use a lot more than 3, to gain both update speed, and reduce the total moving carriage distance needed.eg I get roughly 27 coils on a 1-axis moving PCB can reduce the carriage distance dX to ~30mm while giving a x9 speed up on update time.two more coils can corner-fill the matrix to reduce the dX a bit more.A case of engineering is the art of making what you want, with what you can get.