The adder uses marbles (and the absence of marbles) to
represent bits. The input holder holds one binary number while the toggles hold another. Dropping the input
holder’s marbles adds the input number to the toggle
number, and you can clear the machine for a new calculation by dropping the result onto the result holder.
32
16 8 E
C D 4H
FRONT
A 2
1
BF
See a video of the marble adder in action at makezine.com/go/marble
G
BACK
Illustration by James Provost
The input holder A holds
the next binary number for
the machine to add.
The holder’s holes are
blocked by the input
slider B until the slider is
pushed to the left, allowing
the marbles to fall through.
The toggles pivot around
nails in the machine’s backboard. A marble dropping
onto an empty toggle C ,
representing a 0, rocks it
to the right and is held in
its cavity, incrementing the
corresponding bit.
A marble dropping onto a
filled toggle D , representing a 1, rocks it to the left.
Two things happen as a
result: the captive marble is
released and falls through
to exit down the ramp E ,
and the dropped marble
carries to the left to increment the next bit up. Voilà,
binary addition!
The carry marble is
delayed compared to the
dropped marble, so they
don’t collide.
When you push the result
slider F to the left, it
pushes a slider on the back
of the machine G that
resets all the toggles to 0
and drops their captive
marbles. Meanwhile, it
holds the result in the result
holder H to be read.
Pull the result slider back
to the right, and the marbles
fall through and clear out,
down the ramp. The machine
is ready to perform a new
calculation.
81 Make:
