  The FemtoDAQ is a low-cost two channel data acquisition system which we have
used to investigate the signal characteristics of silicon photomultipliers
(SiPMs) coupled to fast scintillators. The FemtoDAQ system can also be used to
instrument low cost moderate performance passive detectors, and is suitable for
use in harsh environments (e.g., high altitude). The FemtoDAQ is being used as
a SiPM test bench for the High Altitude Water Cherenkov (HAWC) Observatory, a
TeV gamma ray detector located 4100 m above sea level. Planned upgrades to the
HAWC array can benefit greatly from SiPMs, a robust, low-voltage, low-cost
alternative to traditional vacuum photomultipliers. The FemtoDAQ is used to
power the SiPM detector front end, bias the SiPM, and digitize the photosensor
output in a single compact unit.
