Now the mouse outputs a quadrature encoded signal! Quadrature decoder We used a CD4093 with the inputs of the each NAND gate tied together to form inverters. Since it is easier to create a quadrature decoder (in an FPGA) than a serial or PS2 interface, we modified the mouse and replaced the original IC with a quad-buffers Schmitt trigger inputs IC. The mouse includes an IC responsible for the quadrature decoding and the serial/PS2 interface. There are two optical quadrature encoders, each made from a slotted wheel, a light emitter and a pair of photodetectors. If you open a mechanical mouse, here's what you can see. In computer mice, to determine the direction of movement.In robotic axles, for feedback control.Here's an example where an axis moves forward 10 steps, then backward 7 steps. So the idea is that by looking at the edges and levels, we can determine the direction and distance of movement. Now the axis is moving backward by the same amount. If you count the edges, you can say that the axis moved by 12 steps. If you count the pulses, you can say that the axis moved by 3 steps. Here's one axis moving forward by a few steps. They are used in mechanical systems to determine movement (or rotation) of an axis. Quadrature signals are two signals generated with a 90 degrees phase difference. FPGAs are suitable to create quadrature decoders.
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