Hi, I'm working on a project to assist people who are visually impaired read Braille, but I am not sure which sensor I should use to detect the raised dots. To be honest, I am not very familiar with the Arduino sensors, so if someone could give me a rundown on the difference between the various small object detection sensors that would be very much appreciated. Thanks for your help!
Wow, that's a tough one! You need to detect "objects" which are merely slightly-raised bumps in paper and you need to do it for up to 6 simultaneously. Maybe more, if you're trying to read whole words or lines.
I'm not aware of any sensor sensitive enough to find bumps in paper physically. Tiny switches are going to wear down the paper. Magnetic sensors won't work on paper. Ultrasonic sensors can't see that small (the wavelength of the sound is about that order, so ultrasonic will go around the bumps like mobile phone signals go around metal buildings.) Touch sensors like your mobile phone screen are not going to resolve that small.
I'm thinking optical - illuminate it from the side and look for the bumps with a camera. Unfortunately this is beyond the abilities of most Arduinos.
Thanks for your input! Do you know of any devices similar to Arduino that could possibly pull of the optical detection that you mentioned?
I was originally thinking of using touch sensors but I didn't realize that their capabilities were so limited to larger objects. I guess I'll have to keep researching, but please let me know if you think of anything else. 
Well, the common phone/iPod/GPS touchscreens are totally optimised for detecting fingers. They either won't detect a paper bump or they won't resolve 6 of them.
Industrial sensors must exist. Keep looking.
MorganS:
I'm thinking optical - illuminate it from the side and look for the bumps with a camera. Unfortunately this is beyond the abilities of most Arduinos.
Maybe this combined with a pixy to do the image processing.
Touch sensors (such as the capacitive ones used in the Arduino world, or in the form of touch screens) are sensitive to changes in electrical fields caused by touch by a conductive object, such as a finger. They can not detect braille for it's not conductive. You MAY be able to use a touch screen if those dots would be conductive but the paper around it not, and the touch screen can detect sufficient concurrent touches.
I'm thinking optical, too. Teensy may be able to do this, as may the ESP32 (both have 10-20 times the horsepower of a regular Arduino). Otherwise the Raspberry Pi will for sure be able to handle this. The latter will be able to not just interpret the dots (shadows on the camera image) and turn them into letters, then words, but also to synthesise the words and speak them out.
Braille is ment to be read by touch/feel.
Design something that can read alpha characters, oh, they already have this. 
.
But how do you proofread a Braille book? Someone who can read regular text proficiently probably isn't proficient at Braille and will miss spelling errorrs.
Structured light / laser 3D scanning tech might be a possible area to look at. 3D video microscope and some
good CV processing? Sounds fairly costly though. Some sort of prism attachment for a phone camera
to give stereoscopic macro capability + an app? That's likely to be the approach that scales at lowest
cost for the optical methods. Smartphones have a lot of processing power thanks to the GPUs. Worth seeing
if this already exists for other purposes.
MorganS:
But how do you proofread a Braille book? Someone who can read regular text proficiently probably isn't proficient at Braille and will miss spelling errorrs.
You write the book in alpha characters, proof read it, then send the file out to a machine that makes the Braille pages.
amycarleton:
Hi, I'm working on a project to assist people who are visually impaired read Braille, but I am not sure which sensor I should use to detect the raised dots. To be honest, I am not very familiar with the Arduino sensors, so if someone could give me a rundown on the difference between the various small object detection sensors that would be very much appreciated. Thanks for your help!
You would be well advised to do a little research on Braille use before going much farther in your project. It is not a 1 for 1 conversion to a letter in the alphabet. Many abbreviations are used for common words.
Paul
Thank you so much for all of your help! I'll definitely look into using Raspberry Pi and optical detection for this. I'd like to avoid using a smartphone for this since that's not exactly the vision that I have, but if that proves to be the simplest/most cost friendly way of going about this then I may end up with that solution. I've done plenty of research on Braille and understand that there are many abbreviations, and I'm working on a solution for that in my software.