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ST80 Active Wind Transducer
7.2 External Signals
SeaTalk
SeaTalk signals carried by the yellow lead of the SeaTalk cable are routed
directly to the Autohelm ASIC IC5.
Diode D2 placed across the data line and 0V provides limited protection
against lightning strikes.
Incoming signals are converted by the ASIC from SeaTalk duplex line
format to SeaTalk DATA IN format for the microprocessor.
Outgoing signals from the microprocessor are converted from SeaTalk
DATA OUT format at CMOS voltage levels to SeaTalk format at 12V level by
the ASIC.
Anemometer
Pulses are generated by opto - electric integrated circuit IC3, at a rate
dependent on wind speed, by the action of an opto - interrupter on the cup
mounting shaft at the lower end of the assembly.
The output of IC3 is fed via PL1 (round board) and PL2 (main PCB) to
comparator IC3a which uses the reference voltage produced by resistors
R8 and R9 to provide a clean input to microprocessor IC7.
Wind Vane
Hall effect sensors IC1 and IC2 on the round board at the top end of the
assembly detect the position of a magnet mounted on the wind vane shaft.
The resulting analogue voltages (sine and cosine, representing orthagonal
two - axis sensing) are fed via PL1 (round board) and PL1 (main PCB) to
comparators IC3b and IC3d.
The microprocessor sets up bits 1 to 10 on the input of digital - to - ana-
logue convertor IC8, which produces a reference voltage at the output
(VREF). VREF is fed via IC4a to comparators IC3c (cosine), IC3b (sine) and
IC3d (VTEST).
When the reference voltage and the inputs from the Hall Effect sensors
are matched, the outputs of the comparators change state and, as the
microprocessor knows the digit pattern set up to cause this change, the
position of the magnet in relation to the sensors can be calculated.
A test signal (VTEST) is produced by comparator IC3d.
ST80 Active Wind Service Procedures 83067-1 13
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