Make an Automatic Braille Display to Help Blind People

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

Build Your Circuit

Assemble your circuit as shown in Figures 4, 5, and 6. You can also access a Tinkercad simulation of the circuit here, where you can zoom in on the diagram for a more detailed view. Note: depending on where you purchased your breadboard, the left/right orientation of the power and ground buses may be switched.

1. If any wires are too flexible to push into the breadboard (like the solenoid leads), use spring clips to connect them to jumper wires first. 
2. Each MOSFET has three pins: the gate, drain, and source. Each pin should go in its own row in the breadboard. Connect each MOSFET as follows:
   1. Connect the gate pin to an Arduino digital pin (pins 2 through 7 in the diagram).
   2. Connect a diode from the drain pin to +12V from your external power supply, with the stripe on the diode facing toward +12V.
   3. Connect the source pin to ground.
3. Each solenoid has two wires, positive and negative. For each solenoid:
   1. Connect the negative wire to a MOSFET's drain pin.
   2. Connect the positive wire to +12V.
4. Place the button so it straddles the gap in the middle of the breadboard.
   1. Connect one side of the button to +5V.
   2. Connect the other side to ground through a 10kΩ resistor.
   3. Connect the side with the resistor to an Arduino digital pin (pin 8 in the diagram).
5. Connect power to your circuit.
   1. Make sure the entire circuit has a common ground.
      1. The Arduino GND pin should be connected to a ground bus on the breadboard.
      2. Both ground buses on the breadboard should be connected with a jumper wire.
      3. The negative wire from your external 12V power supply should be connected to a ground bus on the breadboard.
   2. Do not short-circuit 5V from your Arduino to 12V from your external power supply.
      1. Connect the 5V pin on your Arduino to one of the breadboard's power buses.
      2. Connect 12V from your external supply to the other power bus.
      3. Do not use a jumper wire to connect the two power buses. This will create a short circuit and can damage your Arduino.

Image Credit: Ben Finio / Science Buddies

Figure 4. Breadboard diagram. Note that Tinkercad does not have solenoids, so vibration motors represent solenoids in this diagram, but the connections are the same. The benchtop power supply represents your external 12V supply.

Image Credit: Ben Finio / Science Buddies

Figure 5. Circuit schematic.

Image Credit: Ben Finio / Science Buddies

Figure 6. Picture of the assembled circuit.

Test Your Circuit

Once your circuit is assembled, you can use the solenoid_test.ino program to test it. This program will activate the solenoids one at a time so you can see if they work. If the circuit does not work — for example, if one solenoid never turns on, or stays on all the time — here are some things you can check:

1. Double-check all of your connections for loose wires, particularly the spring clip connections to the solenoids.
2. Make sure your MOSFETs are oriented properly in the breadboard. Each pin should be in its own row, with the writing on the front of the MOSFET facing to the right and the large metal tab on the back of the MOSFET facing to the left.
3. Check your breadboard for short circuits. Make sure the gate, drain, and source pins for each MOSFET are properly connected separately and that you did not accidentally connect any wires in the same row of the breadboard (for example, connecting a grounding jumper wire to the drain pin instead of the source pin, or a solenoid's negative wire to the source pin instead of the drain pin).

Once you are sure that all six solenoids are working properly, arrange them in a grid of three rows and two columns, as shown in Figures 7 and 8. If you plan to build a more permanent display later, you can temporarily stick the solenoids together using double-sided tape.

Image Credit: Ben Finio / Science Buddies

Figure 7. Solenoid arrangement for braille cell.

Image Credit: Ben Finio / Science Buddies

Figure 8. Solenoids arranged in a grid, attached to each other with double sided tape.

Try Displaying Braille Characters

Once you are sure that all six solenoids are working properly, you are ready to test displaying braille characters.

1. Arrange your solenoids in a grid of 3 rows and 2 columns.
2. Download refreshable_braille_display.ino and upload it to your Arduino. 
3. The default value for the text variable is "hello". Your braille display should show the letter "h," then switch to "e" after you press the button, and so on.
4. Experiment with different words. You can also comment out the while loop that waits for a button press, and experiment with different delays to automatically cycle through the letters. 
5. After testing, unplug your Arduino and 12V power supply so the solenoids do not overheat. 

Build and Test a Better Braille Display

Real braille writing has very smooth, shallow bumps, so the reader can quickly run their fingers over the bumps without getting stuck. The pins of your solenoids are narrow and stick out pretty far, making it hard to easily run your fingertips over them. Can you design a better physical display? For example, you can drill or cut holes in something like a thin piece of wood or cardboard and mount the solenoids to the back with the pins poking through to the front. You could then attach wooden or plastic beads to the pins to create smoother bumps. This is an engineering design project, so we do not have specific instructions for this part of the project — your design is up to you! See Figure 9 for an example with cardboard and plastic beads.

Image Credit: Ben Finio / Science Buddies

Figure 9. Faceplate for the braille display made with cardboard and colored cardstock. Plastic beads are glued to the solenoid pins.

After you have a prototype, you can test it yourself to make sure it is sturdy and that you can easily run your fingers over the bumps. If you know someone who knows how to read braille, you can even have them test it for you. Can they read the word that you enter in the text variable in your program? Do they have any feedback that you can use to improve your design?