CHAPTER 3
3.1
SYSTEM ARCHITECTURE
The grayed boxes in
Figure 1 are parts of the system implemented in software on a microcontroller
unit (MCU). The white boxes are implemented in hardware. A soldier equipped
with the IFF system has a responder unit on their body armor, and an initiator
unit mounted on their rifle. The rifle module uses a laser to transmit an
encoded message. If the rifle points toward a friendly soldier,
phototransistors mounted on the target soldier’s body armor will detect an
incident laser beam. An MCU in the responder unit will decrypt the laser
message using a pre-set private key. If decryption is successful, the MCU
identifies which friendly soldier is currently aiming at the target soldier,
and broadcasts this information in RF. RF receivers in the initiator units of
all friendly soldiers within firing range parse this information to determine
if the rifle they are mounted on is pointing toward a friendly soldier. If
potential fratricide is detected, a buzzer mounted on the rifle goes off,
signaling that the current rifle position might result in friendly fire. This
feedback signal used to trigger the buzzer may also be used to prevent the next
round from being loaded in the weapon’s firing chamber.
3.1.1
Initiator unit:
Fig.3.1.1 Block diagram of the initiator unit.
The initiator unit generates
a laser signal along the weapon's line of firing. The microcontroller generates
a PWM signal that operates a MOSFET switch, which in turn regulates the laser
output. This creates a laser beam that appears to be steady to the observer,
but is actually a very rapid series of pulses with an interval unique to each
soldier.
1.
230 volt, AC input voltage is stepped down to
12V AC using a step down transformer. AC 12 volt is rectified to DC 12 volt
using an bridge rectifier and then filtered.
2.
Voltage regulator LM7812 is
used to regulate the voltage to 5 volt DC. And this voltage is given as input
the micro controller, laser and to the buzzer circuit. Oscillator works at 20
MHz and supplies pulses to the micro controller.
3. If
the code which is stored in the microcontroller is in decimal number. So that
before transmitting it to RF transmitter circuit, code should be converted into
binary format. This conversion from decimal to binary is implemented while
writing the program in micro c software. Hence the encrypted message is sent to
responder unit via RF signal.
Fig
3.1.2 shows the flow chart of sender in initiator part of micro controller
3.1.2Responder
part:
Fig. 3.1.3 shows the responder unit.
1.
The responder unit is responsible for registering laser signals
that land on a user. Photo transistor is being hit by the laser module.
Phototransistor is biased as a common collector, with the collector connected
to an op-amp to amplify the signal. A potentiometer is used to determine the
correct biasing voltage for the op-amp.
2. Supply
to the responder unit is same as given in the initiator unit. It consists of
mainly RF receiver and parallel TX circuit.
3. Encrypted
code received by the RF receiver circuit is decrypted using preset private key
of the micro controller. If this code matches with the already stored code in
the microcontroller of responder unit. Then there exists a feedback signal to
the initiator unit making RFr=1 (High). Buzzer buzzes.
4. Else,
If received code does not matches with the already stored code in the
microcontroller of responder unit. Then there no feedback signal to the
initiator unit making RFr=0 (High). Buzzer does not buzz.
Fig
3.1.4 shows the flow chart of receiver in responder part of micro controller
3.2.1 INITIATOR MODEL
3.2.2 RESPONDER MODEL
CHAPTER 4
DISCUSSIONS OF RESULTS
The encrypted code
sent from the initiator unit in the form of RF signal is received by the
phototransistor of the responder unit. In case (i) valid code is sent and the
buzzer buzzes (i.e. both the unit of microcontroller has same code). In case
(ii) invalid code is sent from the initiator unit. So buzzer does not buzz
(i.e. code which is stored in both the units are different).
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