How a Split-Flap Display Works

here's how a split flap display works

at its core a split flap display has a

motor connected to a spool

that has a bunch of flaps the spool

looks something like this the flaps each

have half of a character printed on them

and they also have pins that stick out

and fit into

holes along the outside of the spool as

the spool rotates

each flap comes to the front and once it

gets past vertical

gravity pulls it down revealing the next

letter

but that's not totally accurate if you

look closely you'll notice that the

window the top of the window is actually

holding the flaps back

if we remove it you'll see that the

flaps

actually tend to clump together and no

longer flip

consistently so it's pretty key to have

something at the top

to make sure that there's a very well

defined

position for the flaps to flip down

if we look at the other side of the

display we'll notice another small

detail that makes

it look and sound great and that's this

flap

backstop right here what that does is it

causes the flaps on the bottom

to gather up and form a more or less

solid barrier

for the flaps to swing into and hit

you can see what a difference it makes

if i remove it

you'll notice that now the flaps swing

freely with all the momentum from

swinging down

it also dampens the sound since the

flaps are no longer hitting

the other flaps at the bottom quite as

hard

it also just doesn't look as good from

the front

so that covers the basic mechanics but

how does the arduino control

whether to show an a or a z

to do that the first key is the type of

motor that we're using

this is a stepper motor which is

controlled using a series of pulses

through this driver

that allows the arduino to rotate the

motor a precise number of degrees

each time however that's not quite

sufficient to fully control the module

for example what happens if we restarted

the arduino right now

how would it know that the z is

currently displayed in not some other

letter

to answer that we'll have to look closer

at this hall effect sensor

the hall effect sensor allows the

arduino to find a consistent home

position by detecting a magnet

in the spool once it finds that magnet

it knows exactly where the spool is

rotated and which letter is showing

the hull effect sensor also allows the

arduino to detect errors

since the arduino is tracking how far

the spool is rotated

it knows exactly when to expect the

magnet passing in front of the hall

effect sensor again

if it doesn't detect the magnet when it

expects it it means something must have

prevented the spool from rotating as far

as it was supposed to

if this happens the arduino returns to

that initial homing sequence

where it searches for the magnet to

recalibrate

so i hope that gave you a good idea of

how split flap displays work

let me know in the comments if you have

any questions all of these designs

are open source and available on my

github which is linked in the

description

thanks