The Mechanically Binary Marble Counter
![[diagram of a sample 3-bit mechanical counter]](images/Counter.png)
The
image to the left is a diagram of my binary marble counter. I built two
so far - one with four bits, one with five bits - with a wooden base
and metal hooks.
How it Works
Each round unit traps a marble with its hook. When a second marble
rolls from the
top, the hook swings to release the first marble and it shunts the
second
marble down a hole. That's a bit - first count to one, then
overflow into the next bit. Simply cascade as many as you need
to count as high as you desire. In the diagram, units 1 and 2 have
trapped a marble and unit 4 has released its marble and is ready to
trap another.
For the purpose of counting, each unit is worth 2 raised to the
power of the number of units above it. The first unit is worth
2^0: 1. The second,
2^1: 2. Then 4, 8, 16, 32, 64. To find the number the machine is
currently showing you simply add the values of each unit that has a
trapped
marble.
When you drop one marble in the machine only the top trap has a
marble. After dropping two, only the second trap has a marble.
When
you drop four marbles into the machine it retains a single marble in
the third trap.
When all the traps are full and you add a marble, the marbles clack and
fall until all the traps have released their marbles. It makes a
great click-clack noise and is fun to watch and hear.
What it Looks Like
![[photograph of the five bit counter]](images/Fivebit-small.jpg)
This is a
photo of my five-bit mechanical counter. It can count quite high
- the five binary traps count all the way to 2^6 - 1 or 31. After that
you multiply the number of marbles in the bottom bin by 32 and add that
to the value of the bits. Since the bottom bin holds eight marbles,
this machine counts to 8*32 + 31 = 287.
Two-hundred-eighty-seven.
I think five bits and a bin may be a sweet spot for a hand-operated toy
like this: you don't need to wory about resetting it to zero very
often and the actual binary-counting part has enough bits to be
interesting. Plus, a larger single unit would be difficult to
make on my scroll saw.
For Your Viewing Pleasure
Here are two small movies, with sound,
of the pictured machine:
Two Bits in Action and
Five Bits Cascading.
![[photograph of the five bit counter]](images/Fivebit.jpg)
This is a
photo of my five-bit mechanical counter. It can count quite high
- the five binary traps count all the way to 2^6 - 1 or 31. After that
you multiply the number of marbles in the bottom bin by 32 and add that
to the value of the bits. Since the bottom bin holds eight marbles,
this machine counts to 8*32 + 31 = 287.