Hall Research VSA-31 - Manual (Page 6)

Model VSA-31
6
As seen in the above diagrams, the connection between the receiver and
the projector are comprised of VGA, S-Video, and RS232. These cables
are not supplied and must be purchased separately.
Please note that most projectors use a unique and non-standard Serial
input connector, therefore you need to build your cable according to the
pin out provided be the projector manufacturer or purchase a cable from
them.
If you will be making your own cable, the VSA-31 receiver has the
following RS-232 pinout:
Connector on VSA-31:
DB9-Male
Transmit: Pin 3
Receive: Pin 2
Ground: Pin 5
Note on video signals that go to the Projector
When you select either of the 2 VGA inputs, the VGA output
to the projector has the selected signal and the S-Video
output is blanked out. Conversely, if the input is Composite
Video or S-Video, only the S-Video output to the projector will
have a signal. This means that it is possible to use the
projector’s auto-detect mode to switch between video inputs
and not even connect the serial port to the projector.
However in doing so, you will not be able to use the on/off
button on the sender to control the projector, and you will
still have to rely on the projectors remote to turn it on and
off.