Rutgers Physics Student Response System

The Substation

Each substation controls up to eight subsubstations, and thus a maximum of 128 student stations. In our lecture hall the substations are mounted on the ceiling of the storage room under the seats of the lecture hall. Each subsubstation is connected by a 15 conductor cable, through a hole in the floor, to its substation. The substation controlled by the signal distributor, to which it is connected by two cables of differentially driven pairs. One, which goes to all substations in parallel, carries 17 control signals to the substations. The other cable individually connects each substation to the distributor and carries five signals, four row outputs and one LE latch input.

The substation provides power and the polling lines (D0-D5) in parallel to all the subsubstations. It receives the four row inputs from each, and multiplexes them according to control signals (SS0-SS2) which it receives from the controller. The four outputs of the multiplexer are sent to the distributor. It also latches the eight light-enable signals, which are part of the 17 signal control cable, with the individual LE latch pulse.

More details of the substation:

Revised: October 10, 1995