  A Scanning Tunneling Microscope (STM) is one of the most important scanning
probe tools available to study and manipulate matter at the nanoscale. In a
STM, a tip is scanned on top of a surface with a separation of a few \AA.
Often, the tunneling current between tip and sample is maintained constant by
modifying the distance between the tip apex and the surface through a feedback
mechanism acting on a piezoelectric transducer. This produces very detailed
images of the electronic properties of the surface. The feedback mechanism is
nearly always made using a digital processing circuit separate from the user
computer. Here we discuss another approach, using a computer and data
acquisition through the USB port. We find that it allows succesful ultra low
noise studies of surfaces at cryogenic temperatures. We show results on
different compounds, a type II Weyl semimetal (WTe$_2$), a quasi
two-dimensional dichalcogenide superconductor (2H-NbSe$_2$), a magnetic Weyl
semimetal (Co$_3$Sn$_2$S$_2$) and an iron pnictide superconductor (FeSe).
