Nuts and Volts - October 2015

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.