by Nyssa Hughes and
As promised, we continue our series on new uses for Das
BlinkenBoard. This month, we feature an amazing and simple mod
from the "UnfocusedBrains" of James Delaney and Nyssa Hughes.
By adding a Hall-effect sensor and a 2K resistor, they have turned
the mild mannered Das BlinkenBoard into a magnetic field
detector! It uses the LEDs as a bar-graph to display both relative
field strength and magnetic pole polarity of magnets held near the
sensor. In their own words, here's how James and Nyssa did it:
Because our home laboratory was without a way to measure
relative magnetic field strength, we figured it was time to build a
simple Gauss meter. Turns out it was really easy! We started by
reading a few datasheets, then settling on a Honeywell SS49
analog position sensor (which is a type of Hall-effect sensor). By
connecting the part to a voltmeter, we were able to detect magnetic fields from various magnets and read voltage levels from the
SS49 to determine the
field's relative strength.
Not wanting to stop
there, we decided to
build a steam-punk
inspired "prop" version of
a magnet detector.
Fortunately, we had a
Das BlinkenBoard on
hand, so James built a
cable to connect the
SS49 to the BlinkenBoard
(FIGURE A). When it
came time to program
the microprocessor on
the BlinkenBoard, James
ran into some challenges
when he discovered that
the datasheet for the SS49 sensor was very confusing. Our friend
Paul Atkinson came to the rescue (he always seems to be helping
us out!). He read the datasheet and told James that a 2K ohm
"load" resistor would be needed to make the SS49 work according
to specifications. We simply added the resistor and Der
Magnetfelder Detektor (DMD) was born.
Now that we had the unit working, the final step was to build
a snazzy case in which to place the electronics. Since this is a prop
version of a magnet detector, we decided to build it as a piece of
foam covered in an ink jet
color-printed "skin." Nyssa cut
two pieces of foam into a 3" x
5" rectangle to make the case
deep enough. She then cut a
BlinkenBoard-sized hole in
both pieces. As James
designed the custom graphics
FIGURE A. Schematic showing how
to connect the SS49 to the
FIGURE B. The printed cover for
“Der Magnetfelder Detektor.”
gallon water jug was sitting on a cooler by the kitchen
table where I was sketching. I envisioned the jug filled
with ping pong balls (like a gumball machine) and a motor
"stirring" the balls to make sure they flowed down the bottle
neck to the printer. I figured that would make a simple
and easy "hopper" to feed blank ping pong balls into the
printer. It looked good on paper and once built, it worked
fine with a handful of ping pong balls. However, once we
for the skin, Nyssa glued the
two pieces of foam together.
The graphic was printed,
sprayed with a layer of
protective acrylic, and cut
out (FIGURE B). The SS49
sensor was taped to the back
of the paper, with the sensor facing up (FIGURE C).
Next, Nyssa stuffed the BlinkenBoard into the foam frame
with the circuit. This allowed room to run all the cables for the
LEDs in the space beneath the circuit board. She pushed the SS49
sensor cable into a gap between the circuit board and the foam,
and plugged it into the circuit board.
Then, it was time to glue the graphic to the foam and drill the
holes. The graphic was glued only to the face of the DMD. Using a
drill press made quick work of the eight holes. With the holes
drilled, Nyssa was about to stuff the LEDs through, but first
needed to figure out which LED was "South." The first LED in the
series is the one that goes into the South hole. The eighth LED is
the one that goes into the North hole.
The LEDs were poked through the holes in sequential order.
After some adjustments, the LED cables got organized, plugged in,
and taped down. Nyssa poked a hole into the side of the paper-covered foam through
which to run the power.
She glued the sides of the
DMD and added some
foam feet (FIGURE D).
Now it was time to
play with magnets! By
holding a magnet to the
DMD's printed button, you
can determine the general
strength (i.e., one LED
versus eight LEDs) and the
alignment of the magnet.
If the bar graph starts on
the North side, you are holding the North pole of the magnet to
the sensor and vice-versa.
Please let us know if you configure your Das BlinkenBoard as
Der Magnetfelder Detektor. Also, please let us know if you do
something fun and interesting with your own Das BlinkenBoard.
You can send your emails to email@example.com.
FIGURE C. The Das
BlinkenBoard mounted in
the foam enclosure.
FIGURE D. The Cables and foam feet
on the bottom of the foam case.
Honeywell SS49 Sensor
James Delaney’s Blog
Nyssa Hughes’ Blog
Das BlinkenBoard Web Page
filled up the entire water jug, the first problem appeared.
At the beginning of the print cycle, the stirring rod
system would activate as designed but, instead of the balls
mixing around, they would "stack up" and stick to each
other. This would cause the stirring rods to bind and
resulted in the motor attempting to back spin, twisting
and eventually tearing up the motor wires.
Upon closer inspection, we discovered that — unlike
November 2009 63