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
(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
C1 is a capacitor
to prevent sudden and spurious changes of this voltage that may cause false
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
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