A quadrature encoder provides a way to let hardware read movement (and direction) of a shaft, and they can be simple, effective, and inexpensive devices. But [Paulo Marques] observed that when it comes to reading motor speeds with them, what works best at high speeds doesn’t work at low speeds, and vice versa. His solution? PicoEncoder is a library providing a lightweight and robust method of using the Programmable I/O (PIO) hardware on the RP2040 to get better results, even (or especially) from cheap encoders, and do it efficiently.
The results of the sub-step method (blue) resemble a low-pass filter, but is delivered with no delay or CPU burden.
The output of a quadrature encoder is typically two square waves that are out of phase with one another. This data says whether a shaft is moving, and in what direction. When used to measure something like a motor shaft, one can also estimate rotation speed. Count how many steps come from the encoder over a period of time, and use that as the basis to calculate something like revolutions per minute.
[Paulo] points out that one issue with this basic method is that the quality depends a lot on how much data one has to work with. But the slower a motor turns, the less data one gets. To work around this, one can use a different calculation optimized for low speeds, but there’s really no single solution that handles high and low speeds well.
Another issue is that readings at the “edges” of step transitions can have a lot of noise. T ..
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