Issue 1.1 18/07/03 SIMRAD
18
Solenoid Drive. The solenoid drive is switched by logic levels from port P3.5 of the
microprocessor. Components TR7, R30, R31, R32, R33 and ZD2 convert the logic level to
a higher voltage level to enable the FET TR8 to be switched. Diode D5 is used to block
inductive ‘kick’ generated from the solenoid coil.
EMC. Capacitors with values of 100pF, 100nF and 1nF are extensively used to decouple noise
from switched data lines. The 3 100nF capacitors C35, C36 and C37 provide AC coupling to
reference the gearbox metalwork to 0V. The connections are made through the 3 screw holes
which fix the PCB to the gearbox.
Factory Test Facility. Transistor TR60 and associated circuitry provides factory test facilities and
is not normally fitted.
SFC12 PCB Assembly
Introduction. The Control Unit SFC12 acts as the interface between the Powerpilot and the user
via switches, LEDs and a buzzer to facilitate a 2 way flow of information. The circuit diagram for
the PCB is given in Drawing No. E02882.
Supply and Regulation. The SFC12 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 provides a 5V regulated supply from which the internal circuitry is powered.
Microprocessor and Reset. Integrated Circuit IC1 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 IC2 either controls or receives data
from the remainder of the circuitry as follows:
LED Control. Each of the 5 LEDs (LED1 – LED5) is controlled by a PNP transistor (TR1 –
TR5) which in turn are controlled by the microprocessor ports P3.0 – P3.4. Across the
emitter and collector of each of these transistors is a bleed resistor which enables the LEDs
to be constantly on, but only very dimly, to facilitate night vision of the keys.
Buzzer Control. Whenever a key is pressed or an alarm is indicated, the buzzer AR1 will
sound. This is controlled by Tr6 and TR7 which are in turn controlled by the
microprocessor port P3.5.
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 Rotary 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.
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