Braille Cell Array Drive Circuit

A project log for Electromechanical Refreshable Braille Module

Lowering the cost of Refreshable Braille Cells by using Electromagnetic Cam Actuators & 3D Printing

vijayVijay 09/10/2023 at 17:442 Comments

I'm working on the drive electronics to actuate pins for an array of braille cells that can make up a full braille display.

I have been looking into the functioning of Flip-Dots, as they share many similar characteristics to each Braille-Cell dot.

Flipping Dots Fast. | About using electronic stuff

                 Above: A single Flip dot toggles its position when the polarity of an electromagnet is changed.

          Above: A single Braille dot toggles its position when the polarity of an electromagnet is changed.

Luckily, there are several projects on Hackaday to learn from (Hackaday community seems to love these). I found these amazing mechanical 7-Segment displays from AlfaZeta that are a perfect analogy for the Braille-Cell, each segment works just like an individual flip dot, and 7 segments of them are packaged into a module where each segment need to be energised only momentarily and then retains its state, similar to our 6-dot Braille Cell:

I found a project that just "Throws H-Bridges" at the module to drive them, but I wanted to be able to save on money and microcontroller pins to create a more elegant solution, and keep the cost lower than the 10$ per Braille-Cell goal I have for the project: 

I came across this video by YouTuber GratScott! that showed an array of these modules controlled by some interesting electronics:

The circuit on this is what Ive decided to reverse engineer as best as possible for a using 6-dot braille cells.

How the driver works (I think), taking the example of driving 5 Braille Cell Modules:

Download the Schematic above here:


Questions/Doubts I have:

Download the Schematic above here:


kelvinA wrote 09/11/2023 at 15:38 point

Looking at the TBD62783APG datasheet, it seems that the clamp diodes are specifically added so that inductive loads are driveable. 

You might want to consider connecting RESET to !E1 and/or !E2 on the 3-to-8 source decoders (where SET is E3) to prevent the shoot-through condition.

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Vijay wrote 09/11/2023 at 19:45 point

Great Idea, prevent any mistakes from happening, thankyou!

I tried simulating the circuit on SPICE, but it would give unpredictable behavior when I connected the Source and Sink array outputs on each of coil side. It works when I test the SET and RESET circuit in isolation, but it seems like you cant just connect these together like in a H-Bridge.

While researching today, I found another project that uses a similar circuit:

The flip dot circuit it drives has additional components, mostly an array of dual-switching diodes :

Adding these into the circuit seems to have got it to work on SPICE, to be seen what happens to it in real life.

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