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8/25/2005
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Review: Smart Golf Clubs

The Intelligent Club from SmartSwing is a golf club that has the smarts built in to analyze the speed, acceleration and swing plane of a golf swing.

I've done a lot of teardowns over the years. One of the fun parts about doing these articles is that I get to use the product for a short time before I dismantle it. I can honestly say that I had more fun "using" this product than any other I've taken apart. The Intelligent Club from SmartSwing Inc. is just what the name implies-a golf club that has the smarts built in to analyze the speed, acceleration and swing plane of a golf swing.

I won't go into the details of its analysis of my own swing. Suffice it to say I'm glad it didn't have a "laugh" mode. But the club operated as advertised. It works like this: you take some simple measurements of yourself holding the club and plug them into the SmartSwing software. You hit some balls at the driving range, then wirelessly download the swing information to a PC. That's it.

I was pleasantly surprised at how well the club performed. But I was even more impressed when I took the club apart and saw how much was crammed into a very tight space, a tube measuring about .5 inch in diameter. The board itself measures 7 3/4 inches, with the battery adding another inch. Together they weigh just under 1 ounce. Most of the hardware and firmware was designed by Evermore Systems (Austin, Texas), an external design house. The software was written by the SmartSwing team, also based in Austin.

"The hardest part was the trade-offs that had to be made to make everything fit," said Alex Gabbi, SmartSwing's chief operating officer. "We obviously had limited board area and that severely limited the components we could use. So we had to make trade-offs in virtually every aspect of the design."

Lots of trade-offs
One trade-off was in the efficiency of the power consumption. Switching power supplies would have been the most efficient, but there wasn't enough board space to go that route. So a compromise was made, using just one switching power supply to convert the battery's 6.2 volts down to 1.8 V. At other points, smaller but less-efficient linear power supplies were used.

The antenna design was a key challenge in that it had to broadcast out of a metal shaft at 2.4 GHz. That feat was compounded by the fact that the antenna had to be placed next to the power connector, a pushbutton and an LED.

Gyroscopes from Analog Devices record the golfer's swing plane. Here, there weren't too many choices. But there were many choices for the accelerometers, which record the speed and acceleration of the club head. Again, Analog Devices components were chosen, mostly because SmartSwing believed they offered the best combination of dynamic range, power consumption and footprint for its requirements.

"We hit the projected bill of materials," said John Lupher, president of Evermore Systems. "However, we were working less toward cost and more toward the functionality of the product, trying to meet the specifications. The strategic directive was not really cost-driven for the first generation. We figured that would come in the second generation."

The wireless data transfer needed a rate of around 1 Mbit/second. The low-cost option that fits the board-space requirements (barely) is the CC2400 2.4-GHz RF transceiver from Chipcon.

In addition to looking for cost reductions, the next generation will introduce the concept of a cartridge system. In doing so, the electronics could be transferred from club to club, potentially by the end user, allowing the cartridge to fit into just about every golf club on the market. In its current configuration, it fits in about 80 percent of the clubs available today.

Position fix
The club uses three XRS300 gyroscopes and two ADXL210 dual-axis accelerometers. The 210 has since been replaced by the 310, which offers higher performance in a smaller package. It's 4 x 4 mm, as opposed to the 5 x 5-mm package of the 210.

The 210 has a gravitational force of 10 g's, while the 321 goes all the way to plus/minus 18 g's.

The 210 measures acceleration in the three axes, X, Y and Z. With the gyroscopes, it measures rotation in the three axes. Hence, the club can record the club's position in space at any point in time. This is done at about 1 kHz. Velocity is measured using the acceleration over time.

On the power side, op amps and analog-to-digital converters from Texas Instruments were chosen. Specifically, a TI OPA2340 amplifies the signal coming from the accelerometer and sends it through the 8325 high-speed data converter. From there, the signal is passed to the Philips LPC2106B microprocessor, which is based on a 16/32-bit ARM7TDMA-S core supported by STMicroelectronics' M25P32 32-Mbit serial flash chip.

The design also takes advantage of TI's battery charger. Final communication back to the host PC goes through a TI TUSB3410 USB device, which also handles the battery charging. Other TI components (about 30 in total) include a TPS62202 dc/dc converter and some TPS770XX series low-dropout regulators.

Temperature compensation is handled with a digital temperature sensor, the TI TMP100, housed in a SOT-23 package. "There's a need for accurate temperature measurement on the board, because the MEMS [microelectromechanical systems] act differently based on the temperature of the environment," said Chinh Vu, a distribution business manager at TI.

The 210 series retails for $699.

Richard Nass (rnass@cmp.com), site editor of CommsDesign and WirelessNetDesignLine

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