Electronic Braille cell prototype

[Ross_Hill]

I need to prototype a refreshable braille cell as cheaply as possible. Basically I need to make a series of pins move up and down in response to a computer input. Any ideas on where to start with this would be greatly appreciated

Thanks
Ross Hill

 

[KMoffett]

Interesting project. What's the size of your intended Braille "letter" 2x6 matrix? Are you thinking of one Braille letter that changes as words scrolls by, or a line of letters that changes with with a new line of text?
The devil's in the details.

Ken

 

[Ross_Hill]

Hi ken,

For starters im just looking to produce a 2 x 6 matrix as you say. If I can just get it to scroll through the characters of the alphabet it would be great. I have achieved this with an LED matrix using an Arduino setup. But im struggling with regards to moving it onto pins which can display the character through a surface. Any actuators I have come across seem to be too large and too expensive.

 

[KMoffett]

You might think of using solenoids that are too large to fit directly under the letter, but driving pins through something like small, flexible bicycle brake cables/sleeves.

ken

 

[MrAl]

Hello there,


Are you talking about the 2x3 array used for the Braille alphabet? That is just three bumps along side three more bumps right?
You could do this with 6 solenoids. They dont have to be small if you use an offset arm from either 3 of the 6 or perhaps
all 6. The arms would look something like this:

         touch
          |  |
          |  |
   -------+  +-------
   |                |
   |                |
   S1               S2

This shows two solenoids S1 and S2 and two arms only.
Note that in the full scheme, there would be 6 solenoids and 6 arms, where the 6 solenoids are mounted
in two columns of three each, side by side somewhat close together, and 4 arms are oriented on 45 degree
angles and 2 arms are oriented horizontally.

\ /
- -
/ \

 

[KMoffett]

OOPS! That was 2x3 not 2x6.

ken

 

[MrAl]

Here's a slightly better drawing showing the arm arrangement and the solenoids viewed from the top:

  S       S
   \     /
    \   /
     . .
S____. .____S
     . .
    /   \
   /     \
  S       S

This arrangement allows the use of any size solenoids, the arms just have to be attached to the solenoid shafts and
probably have some guide shafts to keep the arms oriented correctly.

Alternately and probably better, use 6 levers instead of arms, with 6 guide holes drilled to keep the tip of the arms
in place.

Maybe also a switch that the user can hit when they want to 'display' the next character?

 

[Ross_Hill]

Yeah this seems to make good sense. Can you make any suggestions as to what type of solanoid I should look for and where I might find them. Baring in mind that it only needs to move up by less than 1mm.

Thanks again

 

[MrAl]

Hi again,


Well that's one way to do it anyway. As far as the solenoids, probably any low cost model would work. You might get some
in the surplus market and do some experiments. You'll also need transistor drivers or something like that.

Just curious, what are the dimensions of the columns and rows, ie how far apart is each 'dot' supposed to be vertically and
horizontally, or is the standard a little more flexible?

 

[crutschow]

You might look at how an old dot-matrix printer works. They print letters with a row of small solenoid operated pins that move only a short distance.

 

[Mr RB]

That's a good idea, you could get an old 9-pin dot matrix printer head which already has 9 solenoids driving 9 pins, and mechanically modify it.

 

[Ross_Hill]

http://www.mkdesign.free-online.co.uk/braille_cell_size.gif - here are the sizes I need to replicate

 

[Roff]

Apparently , existing technology uses piezoelectric actuators. Have you researched these?
Refreshable Braille display - Wikipedia, the free encyclopedia
**broken link removed**

 

[MrAl]

Hi again,


I like the printhead idea if in fact we could find a printhead in these days that is not too expensive, and that the dimensions are right.

I also considered using speaker coils but might like the force available in a solenoid better.

 

[KMoffett]

Though too gross, I wonder if something like this could be scaled down to your purpose.
**broken link removed**

ken

 

[phoenox]

You could wrap wire around the pins, add one permanent magnet under the cell for the pins to push off of.

 

[Hero999]

How about using tiny electric shocks rather than bumps?

You might think that sounds crazy but if you get the current and frequency right, it won't hurt, it'll just feel like it's vibrating or even warm if you go for a really high frequency.

A double layer PCB with no solder resist on one side with a via for each electrode could be used. The pulses to the electrodes could be multiplexed.

Obviously you'll need to ensure that it's impossible for any failure to produce a dangerous shock, also note that if the power doesn't flow through the heard, the worst it can do is really hurt and burn and if it's designed so the current remains on the surface it's even safer.

 

[Ross_Hill]

Hi guys,

I have spent some time sourcing the right solenoid and now set up a rig on which it can work. I now need to connect the 6 solenoids to my arduino board to enable me to control them with code. As mentioned earlier my electronics skills are quite limited, wondered if anyone knew how I might set this up on a breadboard, expect I will need a transistor and diode. The solenoids im using require 6volts.

Thanks

Ross

 

[KMoffett]

The solenoids im using require 6volts.

How much current does the solenoid require at 6VDC?

Ken

 

[Ross_Hill]

this particular solenoid is 1.2watts - so am I right in saying this means it requires 0.2amps at 6Vdc? (told you my electronics arent up to scratch!)

Thanks