a 47K Ω resistor is used. Additionally,
this trimmer pot will enable you to
fine-tune your Diet Buddy’s dark-to-light reaction time.
Step-by-Step Guide
This circuit is built “freeform” —
without a circuit board. Additionally,
the wiring for the LDR (i.e., one GND
connection and a connection from pin
2 of the LM386 IC) is routed to two
solder tabs on the inside of the DB- 9
serial connector plug. Wiring this
connection to the inside of the DB- 9
plug enables the LDR to be “plugged”
into the outside of the DB- 9 hood.
This is aesthetically pleasing and will
make any BEAM builder proud.
Let’s begin:
Step 1. Snip off LM386 pins 1, 7,
and 8. These connections will not be
used.
Step 2. Solder a wire to pin 2 and
connect the wire’s other end to a
solder tab on the inside of the DB- 9
serial connector plug. This connection
will be used by the LDR on the outside
of Diet Buddy.
Step 3. Drill two holes matching
the power terminals of the CR2032
battery holder in the top of the DB- 9
hood. These holes will be used for
routing the V+ and GND wires from
the CR2032 battery holder.
Step 4. Solder one wire to each
of the CR2032 battery holder
terminals and glue the holder to the
top of the hood.
Step 5. Solder the GND wire to a
solder tab on the inside of the plug.
All of the circuit’s other ground
connections can be ganged onto this
tab, too.
Step 6. Connect the fixed resistor
(e.g., 47K Ω) between pin 2 and V+.
The wiper connection on the trimmer
pot (e.g., 100K) is connected to pin 3,
and one of the remaining pot pins is
soldered to V+. The third and final pin
is connected to GND.
Step 7. Ground pin 4 to the
circuit’s GND terminal and solder pin 6
to V+.
Step 8. Attach the vibrating
motor’s positive lead to pin 5 and its
negative lead to GND. Don’t worry if
you get these leads backwards or you
are unable to correctly ID the lead’s
polarity. The motor will just run
“backwards,” but it should still vibrate.
Step 9. Most pancake-style
vibrating motors are supplied with a
sticky pad. Peel the carrier sheet off
from the sticky pad and attach the
motor to the inside bottom half of the
DB- 9 hood.
Step 10. Carefully insert all of the
components inside the DB- 9 plastic
hood and attach the two retaining
screws. Insert the LDR leads into the
two plug receptacles used in steps 2
and 5. It doesn’t matter which lead
goes into which receptacle. Insert a
CR2032 battery into the holder and
test the circuit for light sensitivity. If
your Diet Buddy is calm in the dark
and agitated in the light, it’s ready for
the fridge. If the motor runs
continuously, adjust the trimmer pot
and try to balance the light/dark
resistance values.
Diet Buddy is now ready to help
you watch your waistline. Now, all we
need is a robotic drill sergeant to get
your couch potato butt up and turn
you into a lean, mean bot-buildin’
machine that matches your brawn
with your brains. SV
SERVO 12.2014 57
Make a Donut Run
A recent study suggests that reduced
exercise might contribute more to obesity
than increased caloric intake. The data,
analyzed by the National Health and
Nutrition Examination Survey (and
subsequently published in the American
Journal of Medicine) found that during a 20
year span between 1988 and 2010, US adult
women who reported no physical activity
jumped up from 19.1% to 51.7%. Similarly,
during the same time period, the absence of
physical activity for US adult men increased
from 11.4% to 43.5%. According to lead
investigator Uri Ladabaum, MD, MS,
Associate Professor of Medicine, Stanford
University School of Medicine, the higher
rates of obesity did not show "any significant
population-level changes in average daily
caloric intake." So, you can eat that donut,
just make sure you run to go get it.
