The QuadQuad PCB allows position and velocity information to be read from up to four incremental quadrature encoders simultaneously via SPI. These encoders are typically found on the shaft of a motor, allowing the motor rotation angle and velocity to be measured. When used on a robot wheel motor, this would allow you to measure how far your robot has moved and how fast and makes closed-loop control possible.

I designed QuadQuad with the intention of building an advanced Micromouse, because I was unable to find a part that could do the job required and saw that many designers shared my frustration. The end product turned out to be quite advanced and works really well.

Features: Four quadrature channels (sampled 4x per detent) | Provides position (8, 16 or 32-bit), velocity (12-bit), status and timing metadata | Velocity up to 10,000 transitions/s with precision of 0.1% | Home/index inputs | SPI slave interface up to 2MHz | Streamed data packets up to at least 50Hz with 4x channels | Operating voltage 3.3V to 5.5V | Supports 4x Pololu HP motors at their maximum rated shaft speed of 30,000 RPM | Arduino library and demo available

There are many challenges to accurately measuring encoder velocity on a microprocessor, even more so from multiple encoders. If position and velocity are measured on your microprocessor, it consumes much of your processing power and without using numerous special tricks and peripherals, it is pretty impossible to measure the velocity QuadQuad can. QuadQuad measures all channels simultaneously, which has a distinct advantage over reading separate decoder chips, which have to be read one at a time and the resulting data would be unsynchronized and slow. This synchronization is important if you want to combine feedback from multiple motors to drive in a straight line, do Ackerman steering or detect wheel slipping, for example.

The PCB comes with a block header, allowing for easy connection with an Arduino and quadrature encoders. A complete Arduino library and demo code is available for free, as well as a Datasheet detailing physical connections and protocol. The microprocessor will also be made available for implementation directly onto your own robot in the future.

I hope you like this gadget and further suggestions or requests are always welcome.