TomTom GPS Car Kit for iPhone

TomTom’s GPS Car Kit for iPhones has, apart from the obvious secure mounting, a number of advantages over just running the TomTom Navigation App on an iPhone including: improved navigation accuracy from a built-in GPS receiver, amplified speaker for clearer directions and a built-in re-charger. Unfortunately, the TomTom Car Kit doesn’t include the Navigation App which roughly doubles the price. However, you only have to look as far as customer product revews on Amazon to confirm the improved accuracy provided by the built-in SiRF Star 3 GPS receiver and the improved sensivity helping with obtaining a GPS satellite fix in buit-up (city) environments.

Feature Summary - TomTom iPhone Car Kit

Secure vehicle mounting for iPhone in either portrait or landscape position
Built-in GPS receiver for improved positioning for iPhone 3G/3GS (iPhone OS 3.0 or later)
Battery recharging via the vehicle power outlet (USB connection for power only)
Amplified speaker with volume control for clear turn-by-turn navigation directions
Noise canceling microphone
Auxiliary audio output
Bluetooth for hands-free calling

An iPhone provides a 3.5 inch widescreen (480-by-320-pixel resolution) for the navigation display. The current trend is for larger 4.2 or 4.7 inch widescreen displays so a 3.5 inch display is comparatively smaller. The iPhone specification details a video playback time of up to 10 hours providing a long time for personal navigation mode or road navigation without in-car charging hooked up.

iPhone Built-in GPS Capability vs TomTom Car Kit GPS Chip

The iPhone 3G and 3GS have a Infineon Hammerhead II GPS receiver chip which is targeted at, and commonly used for, GPS enabled cellphones. The Hammerhead II has a -160 dBm GPS signal sensitivity and a respectable signal fix time with 5m position accuracy. New with the Hammerhead II is a new software feature (advanced multi-path mitigation) that avoid gross errors in urban environments resulting from reflected signals from surrounding structures. The iPhone GPS is advertised as A-GPS (assisted GSP) which means it can obtain support from local cellphone bases such as predictive satellite position information and offloading of intensive positioning calculations. It is also capable of autonomous position determination.

The TomTom Car Kit has an integrated SiRF Star 3 GPS receiver with an excellent GPS satellite signal sensitivity of -163 dBm and an autonomous positional accuracy of less than 2.5m. Antenna size can make a significant performance difference and the patch antenna is much larger than that in the iPhone.

In summary the built-in Sirf Star 3 GPS receiver, designed for dedicated GPS navigation devices, improves navigational accuracy over the in-built iPhone GPS which will give performance similar to other GPS cellphones used for automotive navigation. Users will also notice the improved signal acquisition performance in built-up areas.

As mentioned, the TomTom Car Kit has built-in Bluetooth, sensitive microphone and speaker providing the driver with the safety advantages of hands-free calling. Spoken navigation instructions are suspended during phone calls and pick up as soon as the call ends. Although up to eight phones can be paired with a TomTom Car Kit cradle, only one can be used at a time. Neither calls or navigation instructions can be sent through the audio output.

As a note of caution, it is not uncommon for iPhone cases not to fit in the TomTom iPhone Car Kit cradle.