■ FIGURE 5. A nonlinear magnetic field
strength plot for placement of the
magnet 0.05” off the Hall-Effect sensor’s
centerline. Artwork courtesy of Allegro
versions (Figure 6). The standard four
pawn version uses the tactile missing
pawn detection method described
previously. The enhanced six pawn
version uses the same tactile
method, but includes a visual
indicator as well (see Figure 7).
SPECIALNOTE: Because of the
tingling sensation which occurs,
if you have a heart murmur,
pacemaker, or suffer from epileptic
seizures, it’s highly recommended
to go with the visual indicator
The visual indicator has an
encapsulating shroud over an LED and
a micro-lens with which to efficiently
direct and couple its optical energy
down an optical fiber. The 660 nm
(medium red) LED and its optical fiber
(matched to within 10 nm) result
in a minimal index of diffraction
■ FIGURE 6. The six pawn enhanced and the
four pawn standard versions of the kit.
■ FIGURE 7. The IF-E96 LED optical
fiber holding module. Artwork courtesy of Industrial Fiber Optics, Inc.
The Fiber Optic
separate the magnets and Hall Effect
sensors. Be sure to abut the sensors
absolutely flush with the acrylic,
The shape of the flux density
curve greatly depends upon the
magnet’s shape, the magnetic circuit,
and the magnet’s travel path.
Pick Your Pawns
This project comes in two
■ FIGURE 8. A cross sectional view of
the IF-E96 LED optical fiber holding
module. Artwork courtesy of Industrial Fiber
The enhanced kit version’s LED is
a Fiber Optics, Inc., IF-E96. This
visible red LED has a “connector-less”
style fiber optic package per the
manufacturer. The LED’s output peaks
at 660 nm, as previously mentioned.
The internal micro-lens and precision
molded housing maximizes coupling
through extremely precise collet
alignment of the LED into a standard
1,000 µm core plastic fiber cable
(which the kit provides). Figure 8 is a
cross-sectional view of this device that
is ideal for this “magical” application.
You can screw the threaded collet
open and shut. This allows you to
insert the optical fiber, abutting it to
the micro-lens which is between it and
the red LED.
Collets and chucks are closely
■ FIGURE 9. The Bivar Model FLPR-SR
alternate optical fiber holding module.