Quadrature odometers are very common and efficient to provide both a velocity as well as the direction of travel. Two signals are used to report the velocity, the channel A and channel B that is out of phase of 90°.
The convention for a forward (positive) odometer velocity is signal A precede signal B as shown in the diagram below:
Odometer with direction signal
Some odometer has one channel for the velocity (reported with pulses) and an other signal that provides the direction of travel as a logic high or low voltage. As you can see below, if the odometer B signal is high, the velocity is considered to be positive (forward direction).
