Issue 1.1 18/07/03 SIMRAD
19
SHS12 PCB Assembly
Introduction. The SHS12 is the compass for the Powerpilot. Using a fluxgate element it detects
the earth’s magnetic field, calculates the sine and cosine values and passes the information to the
course computer. The circuit diagram for the PCB is given in Drawing No. E02777.
Supply and Regulation. The SHS12 is designed to work from a 12 V source. Protection against
incorrect polarity connection is provided by D1 with protection against over-voltage spikes provided
by ZD1. IC1 provides a 5V regulated supply from which the internal circuitry is powered.
Microprocessor and Reset. Integrated Circuit IC2 is an integrated reset generator for the
microprocessor which produces a reset high pulse of approximately 50mS duration at switch on
and whenever a 5v supply failure occurs. The microprocessor IC4 either controls or receives data
from the remainder of the circuitry as follows:
Bus Circuitry. The Rotary Powerpilot system is interconnected via a single line Rx / Tx data
bus. The bus control is formed by IC3 and its associated components. IC3b takes data
from microprocessor port P3.4 and transmits it over the bus to the other units. D2 provides
protection against incorrect wiring of the unit.
Fluxgate Compass. Two anti-phase signals are provided by the microprocessor from ports
P1.0 and P1.1 These are buffered by TR1 and TR2 to provide drive to the excitation coil of
the fluxgate. A reference voltage of 1.5V is provided by R2 and R3 decoupled by C4. The
2 coils of the fluxgate, mounted at right angles, provide output signals proportional to the
sine and cosine of the earth’s magnetic field. These are fed via IC7, to remove the
reference element of the signal, to 2 dual slope integrating Analogue to Digital Converters
(ADC)s IC 6 and IC5 plus associated components. The outputs of the comparators IC5 are
fed to the 2 microprocessor interrupt ports INT1 and INT2. Accurate timing of the
conversion time is kept by the microprocessor that provides precision analogue to digital
conversion of both sine and cosine simultaneously. Calibration of the circuit to reduce any
errors introduced by component tolerances is achieved via a “pulled cal” initiated by port
P0.1.
SHC14 PCB Assembly
Introduction. The Remote Control Unit provides the same facilities as the fixed control unit with
additional options of: manual control of sea state, alarm set and response speed, dodge facility,
compass read-out and rudder position indication. The circuit diagram for the PCB is given in
Drawing No. E02552.
Supply and Regulation. The SHC14 is designed to work from a 12 V source. Protection against
incorrect polarity connection is provided by D1 with protection against over-voltage spikes provided
by ZD1. REG1 and associated smoothing capacitors provide a 5V regulated supply from which the
internal circuitry is powered. Diodes D6 and D7 and TR4 provide isolation of the supply from the
printed circuit board until the 0V connection is made back to the supply. This prevents partial
conduction via the positive line and bus line through the bus drive circuitry if the 0V line is not
connected and hence prevents lock up of the main pilot circuit.
Interface. Bus interface is provided by IC7b and associated components.
LCD Drivers. LCD driving is provided by IC6 to which data is sent via an 8 bit parallel bus from
the microprocessor. TR3 and associated components including D3 and D4 provide a negative
voltage drive for the LCD. Resistor train R20 to R24 provides the appropriate voltage levels for
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