Rotation detection technology: The wheel in motion also needs to be measured

    Systems with moving mechanical components often have the need to measure what is rotating.

       In cars, the speed of the wheels is needed to operate the speedometer, traction control, anti-lock brakes and cruise control. The engine's RPM should be monitored to control the transmission and keep the vehicle below a safe maximum speed. Power windows are usually controlled by a small motor with closed-loop rotation sensing. And let's not forget that the radio system needs to detect the volume knob (when you turn it) when your favorite song starts playing. In addition
      
    to automobiles, rotation sensing technology is suitable for many other applications and is used in motor shafts, fans, gears, turbines and computer mouse wheels. This figure shows an example of using this technology to determine the flow rate of a fluid:
       
    This type of sensor is called a rotary encoder and is divided into two categories: absolute encoders (they can resolve the exact position in degrees) and incremental encoders (they can detect relative changes). A simple example of an absolute encoder is a potentiometer.
      
    Within the range of incremental encoders, the two main types are "speed only" and "speed and direction". Type 1: The sensor can only generate pulses when any rotation occurs and cannot distinguish between clockwise and counterclockwise rotation. The second type: Direction information can be added and done by adding an additional sensor; the controller in the system can then determine the order of transitions between the two sensors to know which direction the rotation is. Popular
      
Detection Methods for Incremental Encoders The
      
    three most common technologies for incremental encoders are mechanical, optical, and magnetic.

    Mechanical: This method is contact-based, where metal brushes on a rotating disk selectively make contact with metal areas on the stator. On the printed circuit board (PCB), voltage can be applied to a terminal, and the presence of voltage can be detected at the switching terminal when rotation occurs. This is the most primitive method and has several disadvantages:
      
    Friction on the contact surface causes the contact surface to gradually wear over time. The
      
    contact surface will not work well in the presence of contaminants such as dirt and corrosion products.
      
    The bandwidth (detections per second) is largely limited by the brush debounce time, which can be in milliseconds.
      
    The mechanical design and assembly process can be somewhat complex.
      
    Optical: This method usually requires a disk with small holes cut out (mask), a light emitting diode (LED) on one side, and two photodetectors on the other side. Optical encoders offer the highest resolution that any other type of encoder can achieve, with thousands of pulses per revolution, but with tight manufacturing and alignment tolerances. Applications range from computer mouse wheels to high-end semiconductor lithography equipment. A common drawback is its lack of robustness in harsh industrial environments, where any physical contaminants will block the light and sensing can become an issue. Also, LED life is reduced at high temperatures.
      
    Magnetic Technique: A 3-pin Hall Effect Integrated Circuit (IC) matched to a small magnet on a rotating plate is a surprisingly simple yet robust method to measure speed. The DRV5033-Q1 is a good fit here. The sensor can be completely enclosed and isolated from the environment, and the magnetic field of the magnet can travel a distance and is not affected by most types of contaminants in between. To measure speed and direction
      
    using magnetic techniques, the standard solution is to use two latching Hall sensors and a ring magnet with alternating north and south poles. For example, the DRV5013-Q1 and a magnet like this. As shown in the figure below, when each sensor approaches the south pole, it produces a low output; when it approaches the north pole, it causes a high output. The outputs produced by the two sensors are called quadrature outputs - a fancy name for signals that are 90° out of phase.
      
    For any given 2-bit state, there is one unique 2-bit state for clockwise increments and another unique 2-bit state for counterclockwise increments. Therefore, the microcontroller firmware is fairly simple.