■ FIGURE 11. The proper bending
technique for the sensors’ bodies —
push down on the leads and hold
them fast with pliers, protecting the
leads from strain as they enter the
Lengths. The sensors must intersect the
crosshairs in the paper pattern for proper alignment directly below the magnets
for optimum effectiveness and reliability.
We suggest you bend the sensor body
so it just slightly overlaps the Nylon
spacers’ lip (see Figure 11). Ensure that it
faces so the nomenclature on the IC
points upward (see Figure 4 again).
• Hall effect Sensor Handling. These ICs
have extremely brittle, unforgiving leads.
If you incorrectly bend a sensor with the
façade pointing down, you’ll need to rebend it. After several bends, its brittleness
can cause the leads to snap off. Properly
bending and soldering these closely
spaced sensor leads is by far the most
difficult part of assembling this project.
We averaged two solder bridges per
every six sensors installed, and we are
both experienced electrical engineers.
■ FIGURE 12. A PCB multiple footprint
accommodating the pot insertion pattern.
Both versions of the available
kits have two pots: a 10K and a
100K pot. Due to multiple sources of
supply, these components assume
different shapes and footprints; therefore, the PCB accommodates this by a
universal footprint that accepts a
variety of different pots (see Figure
12). This is also true with C1, the 6. 8
µF 555 timer IC’s timing capacitor,
which has three leads (see Figure 13).
This beneficial feature may seem
strange to you. The positive terminal
goes in the center hole. The two outer
holes are for the negative terminals, so
it is impossible to install this polarized
On later versions of the kits, we
use an ordinary two lead polarized 6. 8
µF capacitor since we only had a
limited number of these foolproof-insertion capacitors. The PCB also
accommodates 0.01 µF or 0.02 µF
capacitors with 0.2”, as well as 0.25”
lead spacings (see Figure 14). We
discovered after experimenting and
running tests that the Hall effect sensors
recommended output capacitors may
be either a 0.01 µF or 0.02 µF capacitor.
Assemble the power supplies: Tilt
the switch circuit to connect the 9V
■ FIGURE 13. A three-lead, foolproof
insertion, polarized capacitor.
battery; the 3. 33 volt regulator circuit
(because sensors cannot handle all 9V)
runs the sensors, logic, and LMC 555
oscillators. Bend the tilt sensor leads so
they do not lay flat to the surface
below. This enables the internal ball
bearing to roll away from the contacts.
This opens the circuit and reliably turns
the circuit off when you tilt the box on
its back hinges (see Figure 31 in last
month’s issue to better visualize how
the tilt sensor actually works).
Connect the 9 VDC power supply
or battery to battery inputs and
measure the output of the voltage
regulator. The nominal value is 3. 33
VDC. The worst-case range is 3. 16
VDC to 3. 50 VDC. The selected values of the two programming resistors
ensure they sink enough current to
exceed the minimum output current
required by the voltage regulator IC.
Assemble the LED driver circuit:
R13, LED, Q1, jumper (R10, an electrical short in the form of a simple piece
of wire or clipped component lead), R8,
and pot R9. For the six pawn kit version,
when you mount the LED/optical fiber
holder, screw it in first using the plastic
hardware supplied. Ensure the two plastic alignment nibs (positioning/seating
feet) are properly seated in the two
holes on the PCB right behind the collet. This allows you to solder it without
fear of slippage or improper positioning.
For the four pawn version, make
sure the cathode lead goes in the hole
marked “K” and that the anode lead
goes in the hole marked “A.” The
typical LED has a shorter lead and a
flat on the cathode side of the lens.
Failure to insert a bridge or wire
(short) where R10 goes will cause the
kit to function improperly.
Assemble the 1 Hz oscillator (U6
circuit). Test with a DMM/frequency
counter or use a test lead to jumper a
1 Hz oscillator to LED driver (either
terminal of R8) to verify its operation.
Assemble the 60 Hz oscillator
(U5 circuit). Test with a DMM/
frequency counter or jumper a 60 Hz
■ FIGURE 14. The PCB layout pattern
showing built-in accommodation for
various capacitor spacings.