  This article describes the design, assembly and characterization of a
portable cosmic ray detector, developed by the INSULAB group and suitable for
teaching activities aimed at high school students. It consists of a compact
aluminum suitcase containing three plastic scintillator modules coupled to
photomultipliers, readout by a custom compact electronics chain and powered by
a power bank. The modules operate in coincidence and the system records the
arrival time of each particle and the time over threshold of the signal of each
scintillator module. The data are acquired and processed by a Raspberry PI
connected to a touch screen display for online monitoring. The procedure
implemented for the determination of the detector efficiency is reported, along
with the results of the measurements of the cosmic ray rate as a function of
the altitude and the zenith angle, performed in the laboratory and in different
locations outdoors.
