Rutgers Physics Student Response System
The Subsubstation
The subsubstation is designed to control up to 16 student stations.
It receives controlling signals from the substation via a 15 wire
connector. During the course of one full polling period (55 ms), a six bit
counter (D5-D0) counts from 0 to 47. The least significant 4 bits determine
which student station is being examined, and the highest two bits which
column. Circuitry on the board decodes these six bits and grounds one of the
48 column lines using an open collector IC AND gate. The four row lines
which are in parallel for all 16 student stations are buffered on the
subsubstation, and the light enable (LE) line is converted from TTL logic
to a signal appropriate for driving the LED in the currently selected column.
More details of the subsubstation:
Revised: October 10, 1995
shapiro@physics.rutgers.edu
