EE Times Under The Hood - October 8, 2007 - (Page 72) under the hood: COMPUTERS & GAMING with separate power sources for the motors and the logic. A total of six batteries are generally used, with four running the motors and two running the logic. Motorola opted to go with four total. In making the decision, the idea was to reduce the cost, weight and area required by getting all the power from one set of batteries. However, when the motors were drawing a lot of current, the voltage would slump down and the microcontroller would reset. “It seemed like a good idea at the time. But it’s something we would do differently if we were doing it again,” said Bozzone. Besides that, the package that housed the transceiver caused solderability issues. A QFP, which was not available at the time, would have been a better choice. Nikko wasn’t that familiar with LGA technology, so there was a learning curve for them in using that device. Plus, their factory was very low tech, by Motorola’s standards, which made introducing the part into their process a challenge. There is an identical transceiver, the MC13192, at each end of the transmission—one in the dongle that attaches to the remote and one in the car. The chip is housed in a 5- by 5-mm package. ZigBee, sort of According to Ryan Kelly, a marketing manager for ZigBee applications at Freescale, “They’re not running the ZigBee protocol, but they could have opted for it. ZigBee is the networking layer that runs on top of the 15.4 physical and MAC layers. In other words, the car uses the same radio and MAC software that ZigBee would use, but not the ZigBee software.” But ZigBee is a sophisticated networking layer and would have been overkill for this application. The MCU in the Maserati is part of the MC9SO8GT family. It comes in various flavors, differentiated by the amount of flash and RAM. Motorola is using the GT60. To run the www.eetimes.com • www.techonline.com 802.15.4 MAC, about 60 kbits of memory are needed. As with the transceiver, the same MCU is used in both the remote dongle and the car. The MCU and transceiver communicate over a four-wire SPI interface. There was also an issue with the antenna. The transceiver contained separate transmit and receive antennas, and it wasn’t discovered until too late that they were too close together. The mechanical issues turned out to be easier than the electrical issues, thanks to the expertise of Nikko, who handled all the design aspects of it, like tooling up the parts. The final problem—which cropped up in the final stages—was that the car’s electronics, particularly the wireless subsystem, was susceptible to humidity. Tests performed in the Motorola lab were different from those performed in Nikko’s manufacturing facility in Malaysia, where it’s very humid. That, combined with a not-so-efficient antenna, creates a car with less-than-optimal range. ■ 72 Electronic Engineering Times, TechOnline | October 8, 2007 http://www.eetimes.com http://www.techonline.com http://www.rabbitcorekit.com http://www.rabbitcorekit.com
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