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