Let’s start with a quick explanation of the Doppler effect. We often experience it when hearing the siren of a moving vehicle: the tone gets higher when the vehicle is approaching. The frequency of the acoustic wave emitted by the siren is affected by the movement of the vehicle. This effect is not only true for sounds but also for optical waves: when a laser beam with the frequency f0 is re ected off a moving target with velocity v, its frequency is shifted of a certain quantity. This frequency shift can be measured and therefore a velocity v off a moving target can be calculated. In this experiment we are using the Red Pitaya STEMlab board and the Laser Development Kit in order to measure the custom USB fan velocity.