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Wiring schematic for the North River Railway Odometer
Cars
(B1) is a 9v rechargeable battery
and powers the circuits that deliver a counting pulse to the counter.
(L1) is an infra-red light
emitting diode that will illuminate the axle drum as the car travels along.
(R1) Will limit the current to the
very small amount of 0.003 amps to keep the drain on the battery as small
as possible.
(L2) is the infra-red detector that changes
resistance with the amount of light it receives.
(R2) is a fixed resistor that
develops a voltage swing from about .3 volts to 7.5 volts under ideal
conditions as the drum turns This is much more than is required to trigger
the counter. Unfortunately, you will
find that when everything is assembled this voltage change may be much less
due to less than optimum conditions.
C1 is a capacitor to prevent
sudden and spurious changes of this voltage that may cause false counts.
R3 is a resister that prevents
overloading of IC1 input while allowing slight changes in feedback at this
input.
R6, R7 and IC1 serve only to
improve the reliability of this circuit especially as the main battery
begins to wear down. R6 makes it
harder to turn IC1 “ON” and once “ON” it is harder to turn it "Off.” R7 sets the point at which the on/off
occurs and IC1 amplifies the voltage changes it receives at it input so
that it is either at 0v or close to 7.5v or the full battery voltage. This circuit would work without these
three components under ideal conditions but the mechanical positioning
becomes much more critical for reliable operation.
R4 and R5 divide the voltage of
the pulse signals to the counter in half so that it is lower than that
which might damage the counter.
IC2 is the counter itself and requires
only a tiny amount of power to display its current value so the coin
battery (B2) is sufficient to keep it active for a long time.
R8 is required by the counter as
part of the circuits to drive the LCD display
R9, R10 and C2 work in tandem to
“gently” drop the voltage to the reset pin when clearing the count and then
to allow the voltage to slowly return to high and allow counting
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