The main interest in the construction of a didactic system of data acquisition is to insert the computer in the physic laboratory. In this work we use the microphone entrance of the computer sound cards as an interface to measure time intervals in experiments of mechanics. The system employs light sensible sensors connected directly to mic plug-in of the sound card. The storage and sound analysis of the produced signals when the incident light in the photogate is blocked is carried through free or share softwares. Because of the simplicity and low cost of this method we believe that it can represent a concrete contribution for technological diffusion in the physics teaching.
data acquisition; sound card; microphone plug-in