Not long after that day, I got a note from my friend, Ken Gracey that Parallax would be creating a Propeller-powered convention badge for anyone
who needed such a gadget. The badge we created for
DEFCON 22 was an enormous success, but those are
special and were limited (if you want one, sometimes they
show up on eBay). For reasons I won't trouble you with,
the DC22 badge was a very quick turn-around project, so
we kept the circuitry simple. However, with a better
schedule, the Parallax Conference Badge is able to include
quite a bit more in the way of features:
Parallax Conference Badge (Gen 1)
• Propeller Microprocessor
• 64K EEPROM
• 128 x 64 OLED display
• 6 Blue LEDs (Charlieplexed)
• 2 RGB modules (six LEDs, Charlieplexed)
• 7 Touch pads (used as buttons)
• IR output
• IR input
• MMA7660FC three-axis accelerometer
• AV output (composite video, stereo audio)
This is a nice list of features for a low-cost (~$50)
convention badge. It's powered by a 3.7V LiPo battery,
and even includes a charger circuit. When you plug into a
USB port, the battery gets charged.
As you can see, one of the features of the badge is
the Freescale three-axis MMA7660FC accelerometer. This
is an I2C device, so the connections are
quite simple. Figure 1 shows the
schematic for the MMA7660FC as used
on the badge. No pull-ups are shown for
SCL and SDA, but they are on the badge
near the EEPROM (the I2C buss is
shared).
The schematic is simple, but putting
one of these dudes together isn't — the
chip is tiny: only 3 mm x 3 mm ( 3 mm =
0.12 inches). Have a look at Figure 2 —
the badge on the left is a pre-production
staff badge; the one on the right is a
production model guest badge (the
production badges have a soft on-off
button so you don't have to pull the
battery).
The Propeller is easy to find (biggest
chip on the board). Above that is the
64K EEPROM. Now, have a look at the
tiny chip just above the EEPROM; that is
the accelerometer.
Clearly, this is not something we
want to try to solder at home — even if
May the G-Force be with You
On a recent trip to Disneyland with my
friend, Lynda, she asked me about
accelerators, and if I thought investing in a
company that will provide them to Apple
would be a good idea. Mind you, this is
not really a normal conversation for us. I
work in tech. She works in financial
services. We met in acting class, and most
of our conversations center on the arts.
Still, it was a fun chat that included my
interest in building a portable g-force
meter for roller-coaster riders (Lynda and I
love the California Screamin' coaster). In
the end, I thought her investment idea was
sound — especially when one considers
the continually-expanding smartphone
market, not to mention wearables (e.g.,
Apple Watch, FitBit, etc.) that require
motion and orientation sensing.
■ BY JON MCPHALEN THE SPIN ZONE
10 October 2015
■ FIGURE 1.
MMA7660FC
Schematic.