High Level Design

Our portable security system is able to detect three kinds of security breach:

  1. Touching a door knob.
  2. Opening a door.
  3. Movement in a room.

To complete each objective, we use a different sensor for each task. We built our own capacitance sensor using a touch wire, an operational amplifier, and a few resistors. This capacitance sensor is used to detect a door knob touching. For sensing an opening door, we use an accelerometer. For movement in a room, we use a Passive Infra Red (PIR) sensor.

This project consists of two parts:

The transmitter module consists of one MCU (ATMEGA 16L), the capacitance sensor, the accelerometer, and the wireless RF transmitter. The receiver module consists of one MCU (ATMEGA 32), the PIR sensor, and the wireless RF receiver. Because we are making a portable system, we need to transmit the signals from the door (touching doorknob and opening door) from the MCU at the door to the other MCU at the receiver module. Therefore two MCUs and RF transmiter / receiver are needed.

When a person doorknob, a signal will be sent from the capacitance sensor to the MCU on the transmitter. The same happens when someone opens the door, the accelerometer will send a signal to the MCU on the transmitter. The MCU on the transmitter is programmed so that it can handle the two different sensor triggerings appropriately. An RF transmitter is responsible for sending the appropriate message from the transmitter MCU to the receiver MCU stationed next to a computer. At the receiver, the MCU is also programmed such that it can handle the message from the RF transmitter (either from capacitance sensor or from accelerometer). The trasmitting and receiving scheme will be explained in detail in program design section. Furthermore, the receiver MCU is also programmed to handle signals from the PIR sensor, to interface with a keypad, to trigger an alarm, and to interface with the computer to handle the general administrative actions.

The alarm can be controlled by the computer using UART interface. Each sensor triggering will either display an appropriate message to the PC screen or store the log information into an EEPROM memory depending on whether 'stream' or 'save' or both is activated by the computer. To stop the alarm, you can either use the computer or you have to enter the correct 4 digits code into the keypad. The computer is responsible for setting or changing this 4 digits code, as well as setting the time and date. The computer is also capable of keeping track of the time and date when each of the security system component has been triggered. This can be done by a user by storing the log into the memory. The recorded logs can also be retrieved anytime. Serial connection for the computer can also be disabled. In addition, there is also a clear screen function for the computer.



The standards for this project are: the transmitter is in compliance with FCC rules concerning Radio Frequency Devices located in Part 15 of Title 47 of the Code of Federal Regulations. We operate the transmitter at a frequency of 433 MHz and transmissions are in bursts less than 10% duty cycle.

This project is created for personal use and educational purpose only; and thus will in no way be commercialized and should not infringe on existing patents, if any.