DigitalChickenLabs' Raspberry Pi Pico-Powered OctoQuad Takes the Strain Out of Quadrature Decoding
Designed for use with non-real-time operating systems or lower-end microcontrollers, the OctoQuad handles eight quad encoder channels.
Manassas-based DigitalChickenLabs has launched an eight-channel quadrature decoder powered by a Raspberry Pi Pico board, offering position and velocity outputs over a range of bus types.
"The OctoQuad is an eight-channel quadrature decode module which tracks position and velocity for up to eight quadrature encoders simultaneously at up to a 250KHz pulse rate (up to 1 million counts/s)," the company explains of its creation. "The OctoQuad is perfect for use cases where there is a need to decode many high-speed encoder signals but doing so directly on the system is not feasible."
Powered by a Raspberry Pi Pico microcontroller board installed as a module atop the OctoQuad board itself, the OctoQuad offers a selection of bus types for its decoded data: I2C at up to 400kHz; SPI at up to 1MHz; UART at 115,200bps and a 10-60Hz data output rate; and USB serial with, likewise, a 10-60Hz data output rate.
"Reading quadrature encoders on a Raspberry Pi can be problematic because Linux is not a real-time operating and does not guarantee accurate timing," DigitalChickenLabs says of the need for the OctoQuad.
"Similarly, decoding many high speed quadrature signals on a microprocessor can consume a significant amount of processor time and requires many digital pins. When using an OctoQuad, this processing is offloaded, leaving your processor free for other tasks and removing the need to worry about precise timing."
The OctoQuad is designed to be powered over USB or via a 3.3V input pin, and is 3.3V-only — owing to the lack of 5V tolerance in the Raspberry Pi Pico's design. The company has promised a "wide range of sample code" for using the board with Arduino microcontrollers, Raspberry Pi single-board computers, and desktop and laptop computers — though at the time of writing the GitHub repository had not been made public.
The OctoQuad is now available to buy on the DigitalChickenLabs Tindie store at $44.99 including Raspberry Pi Pico, with a 3D-printed protective case available for an additional $4.99.