Simrad AP12H Service Manual page 20

SIMRAD
Issue 1.2 18/07/03
Supply and Regulation. The SLF12 is designed to work from a 12 V source. The input terminals
are filtered for EMC purposes by L1, L2 and C1. 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.
Main Drive Signal. The crystal controlled oscillator XT1, IC4c, IC4d R2 and R3 provides an
11.0592 MHz signal to IC1 which divides the frequency by 512 to produce a 21.599 KHz square
wave. The square wave is filtered by the network C11, R5, C12, L3 and C13 to produce a sine
wave which is then amplified by IC2 to provide the current, limited by R7, to drive the coil.
Phase Angle Detection and Output. The phase angle of the signal across R7 is compared in
IC3a and IC3b and the result fed to an XOR gate IC4b. The output of IC4b is held high for the
duration of the phase difference across R7 and forms a train of pulses which is developed across
C21 R12 to produce a voltage proportional to the phase change. The output voltage is amplified
by a 2 : 1 amplifier formed by IC5b, R13 and R14 which is employed as the rudder feedback signal
for the system.
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
LCD operation. Oscillation for the negative voltage generator is provided by circuitry associated
with IC8a.
Microprocessor. The microprocessor reads the key matrix S1 to S9 directly, gives the relevant
commands to the LCD and the Bus and provides drive signals to the back-light via TR1 and to the
buzzer via TR2.
EMC. A variety of measures are included in the circuit to limit the susceptibility of the circuit to
interference and to provide reduction of emissions. Extensive de-coupling of the microprocessor
I / O lines is carried out using 100pF capacitors.
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