Sensor performs contactless rotary position measurement

3rd November 2014
Siobhan O'Gorman

Offering designers a reliable replacement for conventional rotary encoders, while providing a software-compatible incremental quadrature output, the AS5601 contactless rotary position sensor has been introduced by ams. Without any change to the host MCU or its application software, the sensor and its magnet may replace a rotary encoder in devices which use rotary knobs.

The AS5601, which is based on ams’ patented magnetic Hall position-sensing technology, is claimed to be more reliable than conventional rotary encoders as it performs contactless rotary position measurement. Mechanical wear and contamination by dust, grease, dirt and humidity cause interference and failure in conventional devices. Interference from external magnetic stray fields is rejected by the robust differential sensing circuit in ams’ sensor.

Allowing for easy configuration, the device’s register settings are accessed via an I2C interface and are saved in on-chip OTP memory.

The quadrature (A/B) output provides between 8 and 2048 positions, offering great flexibility. Therefore, the AS5601 is suitable for off-the-shelf rotary knob or encoder manufacturers, in multiple end products with different output requirements. Suitable for designs that are not directly replacing a conventional rotary encoder, the device is offered with the option of a 12-bit digital output.

Alongside measuring angular displacement, the AS5601 can also detect button presses. A sudden reduction in the air gap between the IC and magnet can be detected by algorithms implemented in the sensor, which generates a PUSH output signal. This push-button function is immune to variations in magnetic field strength due to temperature variations or ageing.

Keeping power consumption to a minimum, the AS5601 automatically enters one of three low-power modes, which reduces the scanning frequency when the device has been inactive for a defined interval. The device consumes 1.5mA in the lowest power mode.

"The clever design of the AS5601’s signal-processing circuitry allows for the provision of a simple quadrature output with which every rotary encoder user will be familiar. This means that solid-state rotary measurement technology is for the first time able to replace unreliable rotary encoders without any need for new software programming in existing designs," commented Heinz Oyrer, Senior Manager for Global Marketing, ams.

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