I want to build a split flap display. I need the least expensive way to determine rotation. Any ideas?wrote 02/03/2019 at 22:51 • 1 point
I want to build a split flap display board, the kind of thing that used to be commonplace in European train stations and airports. (Here's a YouTube video of the board at the Frankfurt airport -- https://www.youtube.com/watch?v=cj32w5z81Ak , and here's a wikipedia page about split flap signs -- https://en.wikipedia.org/wiki/Split-flap_display ).
Integral to making one of these signs is having a way to control the rotation of each character, so it stops at the correct letter. Stepper motors would be perfect, but given that I want to make a sign with at least a couple hundred letters, it became obvious to me that using stepper motors would be way too expensive (both in the cost of all of those motors, and the cost of the electronics to control each of them).
I was thinking a more economical way to go would be to use simple low cost motors, and turn off each character's motor when that character has rotated to the proper letter. That means I need a simple (and inexpensive!) way to detect that rotation. I'm looking for suggestions. Optical rotary encoder? A series of little reed switches on each letter that open and close in various combinations? Some sort of Hall effect thing? Some sort of rotary potentiometer?
I envision each character having about 45 different display possibilities (26 letters, 10 digits, some punctuation and misc symbols), which means I'd have to detect rotational differences of eight degrees or less.
Ideally I'll come up with some simple way to talk to each character, something like sending the desired letter to display to each character via I2C or something. But nothing happens without my first coming up with the most economical way possible to gain feedback / control of each character's position.
What should I do? What would YOU do?