Description
The Auxiliary Input Unit (AIU) provides a means connecting external devices such
as switch contacts, Block Detectors (BD20), or other sensors to the Command
Station via the Cab Bus. These external devices can be anything that supplies an
electrical connection between the input pins (1-14) and the pins marked GND in
Figure 1. These connections can then be read by a computer through the RS-232
port of the command station using the RS-232 commands on page 4. The 14 LEDs
provide indication of which input is active. An LED will light when its
corresponding input terminal is connected to ground. This provides an easy means
to test whether the block detector or other device you have connected to the
terminal is working. Since the AIU is a Cab Bus device (thus it must be plugged
in to the cab bus using the cab bus connectors). Both connectors are in parallel
so you may daisy chain the cab bus through the AIU. The AIU Cab address must
be set to a number that is not used by any other existing Cab Bus device. We
suggest that you set it to a very high number, say between 50 and 63. A DIP
switch is provided to set the address. Only switches 1-6 are active, switches 7
and 8 are not connected. All AIUs ship from the factory with an address of 4 as
indicated by the switch positions in figure 1. If you wish to build your own
sensors Figure 2 provides an illustration of the input circuitry on the AIU. The
series resistor and capacitor provide protection against electrostatic discharge
and some RFI filtering to prevent possible false triggering of the inputs due to
track signals or other noise coupling in to any long wire runs between sensors
and the AIU.
