Mouser - White Papers

Mouser Electronics White Paper While quadrature encoders' high-resolution feedback makes them critical in applications requiring accurate position and speed measurements, decoding these signals efficiently can be challenging, especially in resource-constrained systems. Quadrature Encoded Design Challenges The first challenge with quadrature encoders is signal integrity. All encoders can produce noisy signals: Mechanical contacts can bounce, optical sensors can get dusty, and magnetic sensors may pick up interference. Thus, signal conditioning (often called "debouncing," regardless of the noise source) is needed before decoding to ensure reliability. The need for both debouncing and decoding requires a careful balance of hardware and software resources. Engineers typically choose between hardware-based or software-based implementation approaches, each with its own trade-offs. Traditional Hardware Solutions The traditional approach uses discrete components to condition and decode the quadrature signals. These components typically include: • Resistor-capacitor (RC) networks for debouncing mechanical contacts, • Schmitt-trigger ICs to ensure clean signal edges, and • Dedicated decoder ICs to convert the quadrature signals into count and direction outputs. This hardware-centric approach offers excellent power efficiency since it requires minimal central processing unit (CPU) intervention. However, it impacts the bill of materials (BOM) and demands additional printed circuit board (PCB) area. In addition, hardware solutions can be inflexible. Updating the design to accommodate different sensors or detection algorithms usually requires circuit modifications. Alternative Software Solutions The alternative approach is to handle quadrature decoding in software, reading the encoder signals directly into GPIO pins. This method simplifies the hardware but introduces other challenges. First, the CPU must constantly monitor the input pins to detect transitions. This prevents the microcontroller from entering sleep mode, which results in higher power consumption—a critical consideration for battery-powered devices. The other challenge is timing. The software approach may struggle with timing constraints on resource-limited microcontrollers. The CPU must be fast enough to: • Sample the inputs frequently enough to catch all transitions, • Process the samples through debouncing algorithms, • Decode the quadrature sequence, and • Handle any other system tasks. These timing requirements establish both a maximum detectable rotation speed and minimum pulse width constraints. If the encoder rotates too quickly or produces pulses that are too narrow, the software may miss transitions or misinterpret the sequence. Implementing an Efficient Quadrature Encoder The PIC16F13145 family of microcontrollers (MCUs) from Microchip Technology provides an efficient alternative for quadrature signal decoding. These 8-bit processors incorporate a configurable logic block that brings custom hardware capabilities to the microcontroller domain. The CLB consists of 32 basic logic elements (BLEs), each featuring a four-input lookup table, combinatorial logic, and a flip-flop (Figure 2). An interconnect fabric allows signals to be routed flexibly between BLEs, creating a wide variety of logic functions. This flexible architecture allows the CLB to implement custom logic functions while operating independently of the CPU. Once configured, the CLB can process quadrature signals without requiring constant CPU intervention, enabling the processor to remain in sleep mode and conserve power. Additional power savings and improved system responsiveness can be achieved during active power states as well. This is because the CPU can handle tasks in parallel while the CLB manages the quadrature encoder functionality, meaning less time is spent in active power mode compared to a software approach, where the CPU would need to rely on interrupts and other software latencies to manage the quadrature encoder and other tasks. The responsiveness benefit is due to the CPU's ability to handle separate tasks simultaneously, while the CLB, with its very low propagation delay, reduces delays in determining direction or speed.

• Cover