Simrad AP12H Service Manual page 19

SIMRAD
Issue 1.2 18/07/03
Switches. Microprocessor ports P1.0 – P1.4 are connected to switches S1 – S5 and are normally
high. When a switch is pressed the relevant line is pulled low and the microprocessor actions a
specific task.
Bus Circuitry. The Powerpilot system is interconnected via a single line Rx / Tx data bus. The bus
control is formed by IC3 and its associated components. IC3a receives all data being transmitted
over the bus and feeds it to the microprocessor, via the interrupt port INT1, which then determines
if the data is appropriate. IC3b takes data from microprocessor port P3.7 and transmits it over the
bus to the other units. D2 provides protection against incorrect wiring of other units.
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 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.
SLF12 PCB Assembly
Introduction. The SLF12 Linear Feedback Unit provides a signal proportional to rudder
movement. Mechanical movement is sensed by the change of inductance provided by the
movement of a metal rod, connected to the rudder, through a coil. A fixed frequency is applied to
the coil and, as the inductance varies with rod position, a corresponding change in the signal
phase angle measured across R7 is detected. The change in phase angle produces a linear
voltage at the output of the feedback unit, (varying between approximately 1.6V and 4.7V), for
application to the course programmer. The circuit diagram is given in Drawing No. E03069.
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