In the previous chapter we saw how the baseband complex signal are generated. Let’s see how to detect the movement direction through the phase shift between the I and Q coplex signals!
What are complex or imaginary numbers anyway? According to definition they are defined by the property that i2 = – 1. It’s hard to believe that i really exists, the name “imaginary” originates from the early times when they were concidered as a number system which consit of the square root of negative numbers. Why we need them here? – Because our frequencies can be negative as we will see in the measurements.
Let’s begin the experiment!
The purpose of this experiment is to understand how to build a system whih is able to detect the direction of the movement. It consist of a two channel signal generator and a two channel A/D converter. I recommend to use the Red Pitya which is an extremely powerful signal generator and data aquisition system. For the A/D converter using a microcontroller (or an USB DAQ) might be the most simple solution. Important, that the microcontroller needs to have two independent A/D units (for I and Q). Many cortex controllers do have, I recommend the Cortex M4 based ones. XMC4500F100 or STM32F401RE are both great microcontrollers for this task.