Page 236 - Making PIC Microcontroller Instruments and Controllers

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23' THE COUIIIER$ COUrIfl G IABBLES

wawe Counting marbles, an escapement. (Note the sensor belween ih€ lwo
gales.)

I All the marbles are perfectly round.
I All marblos are the same size,
a A11 marbles have the same densify.
I All marbles are opaque to infrarcd (IR) and light frequencies (Here we are making
the assumption that the IR light does not bounce around and cause us problems This
is not rcally a valid assumptionl)
I All marbles are unifomly colored
I We do not have to count morc thafl 1000 marbles at a time
I The maximum rate of marble flow is 900 marbles a minute (15 per second).
I The marbles will be given to us loose in a cardboard box and are to be l€tumed the

First, let's design a system that counts marbles by allowing them to go one by one
only. In order for Ihe marble! lo be presenled {o the counter one by one. we need an
escapement that will release them one at a time. The following is a schernatic for a simple
two-gate/lever escapement that we can make lt uses two model aircraft Ri/C seflos to
control the two gates that will let the marblos go by one at a time This schematic is fol_
lowed by photographs of a simple escapement that I made in my wood shop in less than
an hour A similar escapement could also be made out of cardboard or hobby materials