This project has 3 basic modules. First module of this project detects if person is entering in room. LCD display placed outside the room displays this status. And if person has entered then buzzer is turned on. Second part of project serves the functionality of a door-latch opening using a password entered through keypad. As well as sending this data to a computer through serial port. This module also turns on buzzer if 3 wrong passwords are entered consequently. User can change this password anytime he/she wish using a keypad. Third module uses LPG gas sensor to detect the gas leakage. If there is leakage then buzzer is turned on.
GSM modem is used to send the SMS whenever there are changes in any of the three modules.

Microcontroller based Ultrasonic Distance meter

The techniques of distance measurement using ultrasonic in air include
continuous wave and pulse echo technique. In the pulse echo method, a burst of
pulses is sent through the transmission medium and is reflected by an object kept at
specified distance. The time taken for the pulse to propagate from transmitter to
receiver is proportional to the distance of object. For contact less measurement of
distance, the device has to rely on the target to reflect the pulse back to itself. The
target needs to have a proper orientation that is it needs to be perpendicular to the
irection of propagation of the pulses. The amplitude of the received signal gets
significantly attenuated and is a function of nature of the medium and the distance
between the transmitter and target. The pulse echo or time-of-flight method of
range measurement is subject to high levels of signal attenuation when used in an
air medium, thus limiting its distance range.

Microcontroller Based Variable power supply

Presented here is an economical and cost-effective yet effiient variable
bench power supply that provides one variable and two fixed supply channels. It
provides 1.2 to 25V supply with up to 5-ampere current through one channel, and
5V, 1A and 12V, 1A supplies through the other two channels. It also displays the
voltage on the output terminals, and the current and instantaneous power drawn by
the load on an on-board LCD display. You can connect this power supply to your
computer via the serial port and see the voltage, current and power drawn by the
load graphically. The project has two sections: the main power module having
linear voltage regulators with rectification and filtering circuitry for supply
generation and regulation, and the other having a microcontroller that is used to
sense and display the current and voltage across the variable supply channel.