Introduction to Rotary Decoders

A rotary decoder is an electronic device that converts the absolute rotational position of a shaft or axle to a digital code. Rotary decoders are used in a variety of applications that require sensing angular position, including:

• Industrial controls
• Robotics
• Automotive sensors
• Consumer appliances
• Audio and video equipment
• Gaming controllers

Rotary decoders encode an analog angular position into a digital format using optical, magnetic, brush contact, or capacitive sensing elements. The digital output code provides a unique combination of bits for each rotational position over a full 360° range. This allows a control system to precisely track the angle of a rotating component.

Types of Rotary Decoder ICs

There are several types of integrated circuit (IC) rotary decoders available:

Optical Rotary Decoders

Optical rotary decoders use photodetectors to sense light passing through patterns on a code wheel or disc attached to a rotating shaft. As the code wheel turns, the photodetectors generate pulses that are decoded into position data.

Advantages:

• High resolution (up to 16 bits = 65,536 positions)
• Contactless sensing
• High reliability

Disadvantages:

• Larger package size
• More complex optical code wheel

Magnetic Rotary Decoders

Magnetic rotary decoders detect changes in a rotating magnet field via Hall effect or magnetoresistive sensors on a chip. The sensors provide a digital output corresponding to the angle of the magnetic field.

Advantages:

• Compact integrated package
• Good resolution (12 bits = 4,096 positions)
• Contactless Hall effect sensing

Disadvantages:

• Requires rotating magnet component
• Lower resolution than optical

Capacitive Rotary Decoders

Capacitive rotary decoders use a set of capacitive electrode segments around a rotating element. The capacitance between the fixed and rotating electrodes creates unique capacitance values for each rotational position.

Advantages:

• Completely contactless
• Excellent resolution (16 bits)
• High reliability

Disadvantages:

• Larger package size
• Complex electronics required

Rotary Decoder Output Formats

Rotary decoders provide position data in several digital output formats:

• Parallel: Multiple direct digital output lines indicate binary position. Highest resolution but requires more pins.
• Gray Code: Adjacent positions only differ by one bit change to avoid errors.
• SPI: Serial Peripheral Interface allows daisy-chaining multiple devices.
• I2C: Inter-Integrated Circuit serial bus requires only 2 wires.

The output format must match the requirements of the control system or microcontroller receiving the position data.

Representative Rotary Decoder ICs

This table shows a selection of common rotary decoder ICs with key specifications. There are many encoder options across optical, magnetic, and capacitive sensing technologies.

Selecting the Right Rotary Decoder

Here are some key considerations when selecting a rotary decoder IC:

• Resolution – Number of bits and precision required
• Output interface – Parallel, Gray code, SPI etc.
• Packaging – Size and pin layout
• Voltage – Compatible voltage levels
• Temperature range – Industrial vs commercial grade
• Cost – Optical tends to be more expensive

The encoder must also be paired with appropriate sensing hardware like code wheels or magnets and mounting components.

Conclusion

Rotary decoder ICs convert angular motion into digital positional data for industrial controls, robotics, automotive applications, and more. Choosing the right optical, magnetic, or capacitive rotary encoding solution requires matching the resolution, interface, cost, and environmental requirements of the application. With the proper decoder IC, accurate contactless rotational position sensing can be readily integrated into new and existing designs.

Frequently Asked Questions

What are the key advantages of using a rotary decoder IC versus a mechanical encoder?

The main benefits are:

• Contactless sensing avoids wear, improves reliability
• Higher resolution options available
• Digital output integrates easily with microcontrollers
• More options for output formats like SPI and I2C
• Smaller package size in many cases
• Lower cost in high volume

What level of resolution is typically needed for industrial vs. consumer rotary encoding?

Industrial controls often require 12-bit resolution or higher (>4000 positions) for precision positioning. Consumer products like audio volume knobs require less, often only 8-10 bit resolution (256-1024 positions).

What is the advantage of Gray code output versus binary output?

Gray code ensures that only one bit changes between adjacent position values. This avoids dramatic jumps if a transient error occurs. Binary code has multiple bits changing, so a transient could cause a larger erroneous jump in position.

How fast can rotary decoder ICs scan position?

Sampling speed depends on the encoder but typical rates are 1 MHz to over 50 MHz. Faster optical encoders are available for very high speed applications. Update rate may be limited by output data rate in some cases.

What is the typical operating temperature range for rotary decoder ICs?

Commercial grade decoders often operate from -40°C to +85°C. Industrial versions from -40°C to +105°C or higher are available for more extreme environments. Wide temperature operation ensures robust performance.