  The DarkSide-50 experiment at the Laboratori Nazionali del Gran Sasso is a
search for dark matter using a dual phase time projection chamber with 50 kg of
low radioactivity argon as target. Light signals from interactions in the argon
are detected by a system of 38 photo-multiplier tubes (PMTs), 19 above and 19
below the TPC volume inside the argon cryostat. We describe the electronics
which processes the signals from the photo-multipliers, the trigger system
which identifies events of interest, and the data-acquisition system which
records the data for further analysis. The electronics include resistive
voltage dividers on the PMTs, custom pre-amplifiers mounted directly on the PMT
voltage dividers in the liquid argon, and custom amplifier/discriminators (at
room temperature). After amplification, the PMT signals are digitized in CAEN
waveform digitizers, and CAEN logic modules are used to construct the trigger,
the data acquisition system for the TPC is based on the Fermilab "artdaq"
software. The system has been in operation since early 2014.
