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MEMS compass packs magnetic sensor, accelerometer

Posted: 07 Jan 2010     Print Version  Bookmark and Share

Keywords:MEMS  accelerometer  magnetic sensor  digital compass 

LSM303DLH MEMS compass

STMicroelectronics packs a three-axis digital accelerometer with a three-axis digital magnetic sensor in a single 5mm x 5mm x 1mm module, aimed at enhancing mobile navigation and location-based services (LBS).

The LSM303DLH system-in-package digital compass aims to accelerate the adoption of enhanced electronic compassing in portable consumer applications, including direction finding, map/display orientation, location-based services and pedestrian dead reckoning in places with no or low GPS signal.

The device adds forward direction orientation that enables application developers to improve the use of limited phone/PDA display size for maps by putting the current user position at the bottom of the map with the rest of the display in the forward (up ahead) direction.

High-precision sensing couples with smart embedded features, including wake-up/power-down function and 6D recognition, which signals if the device is up or down along all three axes (x,y,z).

The device has a linear acceleration full-scale of 2/4/8g and a magnetic field full-scale from 1.3 up to 8 gauss, both fully selectable by the user.

The magnetic sensing element that measures the strength and direction of the Earth's magnetic field and determines the heading relative to magnetic north is based on Honeywell's anisotropic magneto-resistive (AMR) technology.

This technology combines high accuracy in compass calculations with low power consumption, which is crucial in battery-hungry portable devices. The AMR technology provides the same sensitivity on the z axis as it does on the x and y axes, eliminating the need for flux concentrators used in Hall-effect type sensors that can shift the sensor offset after it has been magnetised.

This market-unique three-axis sensing approach reduces measurement errors in ultra low magnetic field strength environments, such as in metal buildings, automobiles, or in higher latitudes like Canada or Northern Europe.

The magnetic sensor design also includes a built-in offset cancellation circuit to minimise the need for calibration, and patented set/reset straps that de-gauss, or de-magnetise, the sensor for each measurement to improve accuracy.

The LSM303DLH module fits in a 5mm x 5mm x 1mm package. Samples are available and the device is ready for mass production.

- Julien Happich
EE Times

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