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Issue 1.0 16/12/99
Motor Drive. Drive signals are generated by the microprocessor and out-
put from ports P1.6 and P1.7, the lines being LOW for no drive and switch-
ing to HIGH to provide drive. These outputs control IC9 and IC10 used as
comparators set at threshold levels of +4V and +1V produced by the resis-
tor network R43, R44 and R45. The signals are inverted and provide cur-
rent to switch the MOSFETS in stages and hence prevent both P an N chan-
nel MOSFETS on the same side of the “H - Bridge” configuration, (TR10 and
TR11 or TR12 and TR13) being partially switched on at the same time.
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.
5.2 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 dia-
gram 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 transis-
tors 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.
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