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7. Circuit Description
Refer to Figure 3, Block Diagram and Figure 5, Circuit Diagram.
Two sensor PCBs (round boards) feed the main PCB. Interconnection and
elements on the round boards are shown in the bottom right corner of
the block diagram.
One sensor (anemometer) detects rotation of the wind cups and produces
a pulse train which is used to calculate the wind speed. The other sensor
(wind vane) detects the rotation of a magnet attached to the wind vane
shaft from which the wind angle is calculated.
The main PCB processes signals from the sensors and interprets mes-
sages from other system elements. SeaTalk sentences containing wind
speed, wind angle and alarm conditions are generated for transmission on
the SeaTalk bus.
7.1 Power Supplies
A nominal 12V supply enters the unit via the red lead of the SeaTalk cable.
Varistor V1 placed across the supply and 0V (black lead of the SeaTalk
cable) provides protection against power surges and voltage spikes.
Diode D1, similarly placed across the supply and 0V, provides limited
protection against lightning strikes.
The input supply is routed as follows:
1. Through reverse protection diode D4 to IC1, a regulator which pro-
vides +5V (Vcc) to the circuitry on the PCB. The output of diode D4
(nominally 12V) is sent through diode D6 to ASIC IC5, as signal VHELD
2. Through diode D3 as signal 12V to regulator IC2 (or alternative fit 8V
regulator IC9).
Regulator IC2 (or alternative fit 8V regulator IC9) provide an 8V supply to
digital - to - analogue convertor IC8. The sensor PCBs (wind vane and
anemometer) are supplied with 8V through PL1 and PL2.
Reverse diode D5 ensures a floating 0V for the circuitry by isolating the
incoming 0V.
14 ST80 Active Wind Service Procedures 83067-1
ST80 Active Wind Transducer
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