  The Cosmic Ray Observatory Project (CROP) at University of Nebraska/Lincoln
and the Washington Area Large-scale Time coincidence Array (WALTA) at
University of Washington/Seattle are among several outreach projects siting
cosmic-ray detectors at local high schools in cities around North America, to
study the origins and interactions of high-energy cosmic rays. In a
collaboration between QuarkNet, the outreach program based at Fermilab, CROP,
and WALTA, a low-cost data acquisition electronics card has been developed to
collect and synchronize the data from each detector site. The cost for each
card is under US$500 for parts, functionally replacing much more expensive
electronics crates and modules at each high school site. The card has 4 analog
discriminator inputs for photo-multiplier tube signals, a 4-channel
Time-to-Digital converter for local coincidence and time-over-threshold
measurements at 0.75 ns resolution, programmable trigger logic via a CPLD and
microcontroller, and a built-in low-cost GPS receiver/antenna module (via
external cable) to provide event trigger time stamps at better than 100 ns
accuracy. Temperature sensors and a barometer are also integrated to record
environmental data along with the counter data. The card connects to any PC or
laptop via a standard RS-232 serial port for data output and control. The
microcontroller and CPLD are field programmable and therefore make the card
functionality flexible and easy to upgrade.
