International Journal of Smart Home
Vol. 7, No. 2, March, 2013
53
4.1.2. Gate Sensor Nodes: The circuit is positioned as the first level of MHSS which
acts as the indicator. Light Dependent Resistance (LDR) is put at a location where it
can detect thieves. Laser diode is used as the light source and the laser beam is adjusted
with a reflector to make the beam fall on the LDR. An input source of 5 V is supplied
to the laser sensor and LDR. They are arranged in a manner that when the laser beam is
blocked by a thief, an output approximately from 3.5 to 4 V is supplied to the LM324,
then it will be compared with the reference voltage of 2.5V. Generally, 5V will be
supplied by LM324 to the microcontroller as a high signal. The laser sensors can be
placed on the wall of the house yard. The output of the sensor, 5V will be directed to
the PIC and the responding signal will turn on the light bulbs that placed at the sides of
the entrance.
4.1.3. Presence Detecting Node: A passive infrared sensor (PIR) is placed at side of
the house yard and the central position of the wall. It acts as the second level of MHSS.
The sensor output voltage is 0.3v when there is no motion detected. When the sensor
senses the motion of a thief, its output range of 3.3 to 5v and it will be sent to the signal
control unit. Then, it will be processed in the CPU and eventually it will make the
webcam start recording.
4.1.3. Break-in Sensing Node: The principle of this stage is similar to the first stage.
The magnetic switch is supplied with 0 signal and the output will be compared with a
reference voltage of 2.5V. When the magnetic switch is opened, an output range of 3.5
to 4v is supplied to LM324 for comparison. Then LM324 will send an output, 5V to the
microcontroller. The output is treated as a high signal, the microcontroller eventually
send an output of 5V to the LEDs and the buzzer as the responding action to the input
signal.
4.2 Microcontroller and UART
The microcontroller used in MHSS is PIC184520 from MicroChip Inc. as shown in
Figure 4. This microcontroller is interfaced to a PC via the Universal Asynchronous
Receiver/Transmitter (UART). UART takes bytes of data and transmits the individual
bits in a sequential fashion. Since the microcontroller makes use of Transistor-transistor
Logic (TTL) level of UART while the PC serial port uses RS-232. Since both standards
uses similar software protocol, both of them are able to communicate via UART.
Figure 4. PIC184520 from MicroChip
(32 pages)
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