Security system MICROALARM. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling

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This device is designed to protect apartments, cottages, garages, etc. The basis of the security system is the 16F84A PIC controller. Arming and disarming is carried out using Dallas Semiconductor DS1990 electronic keys.

The system operation algorithm is as follows: when the registered key touches the reader, and if the door sensor contacts are closed, the system becomes armed. This is signaled by the VD1 diode - it lights up. When the contacts are opened, if the security mode was not disarmed by touching the registered key again, a powerful sound signal is immediately emitted for 1 minute 15 seconds and the LED flashes. If after this time the contacts have not returned to their original state, the signal is given again. If the contacts have returned to their original state, the siren is turned off, but the LED continues to flash at a frequency that is half that of the alarm. This can be used to determine that the device was triggered. When the reader is touched with an unregistered key, a short (1 second) beep sounds and the system remains in its original state. A total of eight keys can be registered.

(click to enlarge)

Chips DA1 and DA2 serve to obtain the necessary supply voltages of +15 and +5 volts. A backup battery is required to keep the device running in the event of a power outage. Its recharging occurs through the diodes VD4, VD5. Fuse FU1, varistor R9, zener diode VD2 are used to protect the reader from external unauthorized actions (for example, applying high voltage to it in order to disable the security system). Composite transistor VT1 controls a powerful siren. The R1C2 chain resets the 16F84A PIC controller, and capacitors C5-C7 protect it from false positives. Button S1 puts the device into key programming mode, S2 erases information about all keys (this is done if one of the keys is lost). It is best to use a motion sensor as door contacts, which has a relay output with normally closed contacts, and power for it is supplied from the security system unit. The reader is installed outside at the front door. A cable can be connected to it, which is connected in series with the motion sensor - in this case, if someone damages the reader, an alarm will sound. The block of the security system with a backup battery and a siren is installed in an inaccessible place.

The procedure for turning on the system for the first time and registering keys is as follows

1. The door contacts (motion sensor) and the RESET button are closed, the PROG button is open.
2. We supply power to the device.
3. Open the RESET button.
4. Briefly press the PROG button.
5. Briefly touch the reader with the iBUTTON keys (up to eight keys).
6. Turn off and after a short pause turn on the device again.
After these operations, the security system is ready for operation.

Item Specification:

When programming keys, fill in all 8 memory cells!

Download Layot files and HEX firmware files

Author: Mikhail Tikhonchuk, alarm [dog] forenet.by; Publication: cxem.net

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