Contactless position sensor is software-compatible rotary encoder replacement

November 03, 2014 // By Graham Prophet
The AS5601 is optimised for use in rotary knobs, and provides an additional push-button function; it gives designers an extremely reliable replacement for conventional rotary encoders, while providing a software-compatible incremental quadrature output.

In devices which use rotary knobs, the AS5601 and its paired magnet may replace a rotary encoder without any change to the host microcontroller or its application software. The device is based on ams' magnetic Hall position-sensing technology, which is already used in the automotive, industrial, medical and consumer markets. Since the AS5601 performs contactless rotary position measurement, it suffers none of the reliability problems with to conventional rotary encoders are prone; interference and premature failure because of the effects of mechanical wear and contamination by dust, grease, dirt and humidity.

The differential sensing circuit in the AS5601 also rejects interference from external magnetic stray fields. Its operation, including its zero position, provides for easy configuration, since its register settings are accessed via an I²C interface and are saved in on-chip OTP memory. The quadrature (A/B) output offers flexibility, providing between 8 and 2048 positions. This means that the AS5601 may be used, for instance by off-the-shelf rotary knob or encoder manufacturers, in multiple end products with different output requirements. Users of the AS5601 also have the choice of a 12-bit digital output, suitable for designs that are not directly replacing a conventional rotary encoder.

As well as measuring angular displacement, the AS5601 can detect button presses. Algorithms detect a sudden significant reduction in the air gap between the IC and its paired magnet, generating a PUSH output signal. This push-button function is immune to variations in magnetic field strength due to temperature variations or ageing.

By default, the device automatically enters one of three low-power modes, keeping power consumption to a minimum by reducing the scanning frequency when the device has been inactive for a defined interval. In the lowest-power mode, the AS5601 draws 1.5 mA. A demonstration board is available.