home security system

Posted on Feb 4, 2014

The basic design of this project will use a Atmel AT89S8252-24PC Microcontroller, since this micro has 2KB of EEPROM that can be used to store data during runtime. A ADC0838CCN analog to digital will be used to receive up to 8 inputs from sensor devices, such as PIR`s, reed switches, etc. The reason behind using an ADC compared to just the DIO pin

home security system
Click here to download the full size of the above Circuit.

s is that it also adds some security by allowing resistors to be put inline to set the voltage to a specific level. If the wire to the sensor is cut or shorted, the alarm will be able to detect this occurring. To Arm/Disarm the system, an RFID tag reader will be used as apposed to a keypad. The chosen reader is a HYE-01 Series LF Reader that has both serial and Wiegand output. For this system the Wiegand output will be used to allow the serial connection to be used to connect to a computer. When looking for information about the Wiegand protocol I found this page useful: The easy way of reading this data is to use the INT0 and INT1 external interrupts and configure them on the falling edge. This protocol works so that when DATA0 is low and DATA1 is high a 0 is produced and when DATA0 is high and DATA1 is low a 1 is produced. In between bits both are high. The final bit is detected when both are high for 50ms, so a timer should also be used for detecting the final bit.

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