Kongsberg Simrad IS12, Service Manual

Page: 38 / 67

Issue 1.0 09/06/03
SIMRAD
38
NMEA In (Mega Instrument Only) . NMEA data in is opto isolated by IC13 and fed directly to the
microprocessor port P8.4.
NB. The NMEA data input employs 2 of the Speed / Log terminals. The Mega Instrument can
therefore only be employed to display either NMEA or Speed / Log data.
NMEA Out (Data and Mega Instruments) . NMEA data out is provided from the Microprocessor
port P8.5 via a driver transistor TR15.
NB. The NMEA data output employs the Depth terminals which must be enabled by fitting a 0_
Resistor R94 into circuit. The Depth and NMEA out functions are therefore mutually exclusive.
Analogue Meter Movement Driver (Wind Instrument Only) . Wind direction information is
supplied in serial data format from port P8.1 of the microprocessor to IC11 which converts the
serial data to analogue drives which are applied to the meter movement directly through current
limiting Resistors R72 and R73.
Log, Speed and Temperature (Speed and Combi Instruments) . The speed transducer is
supplied from the 12v rail via Resistor R80 to energise the Hall Effect device. The returned pulses
are buffered and shaped by Transistor TR16 and associated components and fed to the
microprocessor port P6.6. Protection against high voltage spikes is provided by Diodes D13 and
D14. The thermistor in the transducer is supplied with 5v via Resistor R84 and the voltage
produced by this potential divider network, being proportional to temperature, is fed to the
microprocessor port P7.0.
Depth Sounder (Depth and Combi Instruments) . All functioning of the Depth sounder is
controlled by the microprocessor including the timing of transmit and receive, pulse width of the
transmitter, and all decisions regarding the integrity of received signals and calculations.
Integrated Circuit IC9 is a highly stable tone and frequency decoder which generates a constant
output tuned to 200KHz, adjustable with Variable Resistor VR2. This output, at Pin 5, is fed to
IC8b, c and d where it is gated by the transmitter synchronisation pulse from the processor, Port
P6.0, at the appropriate pulse width 380µS, 1.66mS or 3.32mS. The 200KHz pulse switches on
TR5 which provides a current path for C37 to discharge through the primary of the tuned pulse
transformer CH1 and produces a 450v peak-to-peak pulse which is applied to the transducer
discharging approximately 25w of energy. The transmitter sync pulse is also applied TR6 via IC8a
which mutes the receiver for the duration of the transmit pulse. The supply to the transmitter is
filtered, mainly by C75 and L1, to prevent the high energy transmit pulse causing interference to
other functions.
The receiver is turned on once the transmit pulse is completed and received signals are fed from
the transducer to a variable gain amplifier TR7, TR8 and TR10, TR11 via protection clamping
Diodes D6 and D7 and the attenuator switch TR4. The attenuator is switched in from Port P2.0
when the microprocessor detects that the received signal level is too high, even with the variable
gain amplifier set to minimum, to produce an acceptable level to be fed to the detector, tone
decoder IC9. The decoder output IC9 Pin 8 is normally held high by the pull up Resistor R53 and
thus holds TR9 on. When a signal is detected IC9 Pin 8 is forced low, TR9 cuts off and C47
charges through Resistor R53. This voltage is applied to Pin 2 of the comparator IC10a to be
compared with the threshold stored in C48. The threshold level is generated by taking a sample of
each individual transmit pulse from the source of TR5 and feeding it to C48 via Diode D9. The
level stored in C48 is thus proportional to the amplitude and duration of the transmit pulse. The