Sensor interface IC facilitates implementation of gesture recognition applications

January 18, 2013 // By Christoph Hammerschmidt
The MLX75030 from Melexis is a universal active light sensor interface designed to allow easy implementation of robust multi-channel, close range optical sensing systems into difficult operational environments.

The MLX75030 incorporates four independent simultaneously operating light measurement channels; two taking care of reflection and the other two for ambient light measurement. This optimizes the device for inclusion in human-machine interfaces (HMI) requiring proximity detection or touch-less gesture recognition in environments subject to wide variation in background lighting levels, especially in automotive infotainment systems, white goods and consumer electronics devices.

The Melexis chip features two active light reflection measurement channels with integrated ambient light suppression. The active light sensing section is complemented by two logarithmic current sensors which can measure the photocurrent signal from externally connected photodiodes for ambient light sensing. Internal control logic, configurable user registers and SPI communication enable simple, programmable operation. More channels can be added through multiplexing. A built-in temperature sensor can be used to compensate any heat effects.

It controls the LED current and measures the resulting photodiode signal, which is translated into digital form by an integrated 16-bit analog-to-digital converter (ADC). These data can then be transferred to the system microcontroller via the SPI interface. The optical light intensity of both active light channels can be used to detect proximity of an object close to the detectors, independent from the background light level. Human gestures (such as swipes or zooms) can then be determined by use of software algorithms. HMI response times of 30 frames/sec are supported.

To help meet the most challenging automotive requirements the device integrates auxiliary circuit functions such as: a watchdog timer; CRC, open/short test; internal diagnostics; bias/reference sources; and clock generators.

The MLX75030 is offered in a compact (4 mm x 4 mm), 24-pin surface mount QFN package, or as a bare die. Versions supporting both standard 0°C to 70°C and extended - 40°C to 105°C operational temperature ranges are available.

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