Wireless Home Security System

Transcription

1 Wireless Home Security System Group: D14 Members: Vaibhav Singh (05D07026) Abhishek Tiwari (05D07028) Sauvik Chowdhury (05D07029) 1. Abstract The project is aimed at designing a low cost and reliable wireless home security system. The remote units of the system can be mounted on doors and windows and any intrusion is reported wirelessly to the base station which displays the time of intrusion and the node affected on a PC through a serial interface. 2. Design Approach The project consists of the following parts: Remote Unit : The remote unit has three intruder detection sensors which have been implemented using IR LEDs and the TSOP 1738 IC. The IR LED is driven by a 38kHz signal generated by the microcontroller (Atmega16). The TSOP is sensitive to this signal only. It gives a low output when this signal is disrupted by an intruder. This low pulse is sensed by the microcontroller which then sends the sensor ID to the PC through the wireless transmitter. The remote unit also has a touch sensor which has been implemented using an LM358 opamp and an LM339 comparator.the idea behind the touch sensor is the observation that whenever the strobes of the oscilloscope are touched there are fluctuations in the signal(without any voltage source connected to the oscilloscope). Our design of touch sensor amplifies this signal and uses a comparator for digital output. The output of the touch sensor is high when a person touches it. The touch sensor can be connected to the door knob, which would alert the microcontroller in case of a human touch. The touch sensor is immune to metal and insulators.

2 Base Unit : The base unit consists of the wireless receiver and the MAX232 chip which is used to implement the serial interface. The PC can process the received byte and may sound an alarm or take any other appropriate action. Sensor node Microcontroller RF transmitter PC + Alarm RF receiver 3. Design Strategy : (a) For the intrusion detector we have chosen an IR LED + TSOP rather than using a photo transistor because a TSOP is very selective for the 38 khz square wave. Hence it is immune to variations in ambient light and cumbersome measures such as shielding of photo transistor is avoided. Also the range that we achieved was higher (about 2m). (b) We have used the Atmega16 to generate the 38 khz square wave. For this, we have used Timer 1(16 bit) in CTC mode (Clear Timer on Compare Match). This is an asynchronous timer mode, i.e. it is independent from the task being done by the microcontroller. The Atmega16 also transmits the sensor id to the wireless transmitter by USART (2400 bps). (c) For the touch sensor we have used the LM358 opamp and the LM339 comparator since these are single supply ICs and the remote unit should be capable of running on a battery. (d) We have also included a battery backup circuit in the remote unit. Ordinarily, the unit runs off mains and the battery gets charged. In the event of power cuts, the battery takes over and the security system is still kept running.

3 (e) Initially we were using the CC1000PP module. This was a very expensive module and we were getting a lot of errors in data transmission. We have used the SM -02 TX ASK transmitter and SM -02 RX ASK module ( ) since it is a very low cost RF module and fits all our requirements. It has a range of about 30m which should be sufficient for a home security system. 4. Circuit Diagrams (a) Driving the IR LED :

4 (b) Battery Backup circuit : 5. Results : We have successfully implemented the intrusion detection sensors, each with a range of about 2m. The touch sensor is also showing high selectivity with respect to a person s touch as opposed to touching small metallic objects such as doorknobs. The RS 232 interface is also working properly.each sensor has been given a different sensor ID, and

5 we have successfully transmitted the different bytes to the PC wirelessly. The battery backup circuit is also working. 6. Possible Improvements : A graphical user interface can be made for displaying information.pir sensors can be used instead of TSOP Smoke sensors and shock sensors could also be included.