Security device with iBUTTON key control. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Security device with iBUTTON key control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Safety and security

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The proposed device can perform the functions of a burglar alarm or simply turn on the lighting when a person moves in the room and when the front door is opened. Its scheme is shown in Fig. 1. The basis is the PIC16F84 microcontroller. Its program provides automatic recovery of normal operation after random failures.

(click to enlarge)

Arming and disarming is carried out using iButton DS1990 electronic keys. These very easy-to-use and reliable products are not afraid of moisture and aggressive environment, do not require changing or recharging batteries, as they do not contain them. The code written in the "tablet" cannot be changed. It has 280 trillion options, which virtually eliminates the possibility of picking a key.

The contact device X1, which must be touched with a key to turn the security on or off, is located in any convenient place, for example, on the door jamb. However, the security device itself must be inaccessible to outsiders. Wiring from it to the contact device is carried out with a twisted pair of wires no more than a few meters long.

LED HL1 is used to monitor the status of the device. It can be used to determine whether the armed mode is on, whether the alarm has been triggered for the time elapsed since it was turned on. The security loop, conventionally shown in the diagram as the SA3 switch, is the series-connected output contacts of the IR motion sensor and the SMK reed sensor installed on the door. If there is no motion sensor, the device will only react to the opening of the door.

When the power is turned on, the device starts working in a mode in which, when the loop is opened, it only turns on the lighting. After about a minute, the light will automatically turn off. To switch to armed mode, you need to touch the contact device X1 with the registered key. After reading the key code, the microcontroller prohibits re-reading for 1 s, preventing unpredictable mode changes if the key is held in the contact device for too long.

Arming will be confirmed by a short sound of the HA1 siren and a flash of the HL1 LED. But in fact, the protection will be turned on only after the closed state of the loop is restored (if the latter was open). This allows the "owner" to leave the premises and close the door behind him without causing a false alarm.

In the security mode, the HL1 LED is on, the lighting is off. Violation of the loop leads to the activation of the HA3 siren for 1 minutes and the blinking of the HL1 LED. Then the microcontroller checks the status of the loop again. If it is closed again, the siren will be turned off, but the LED will continue to flash. Touching the contact device again with the registered key will disarm the premises, which will be confirmed by a two-time short-term activation of the siren and the extinguishing of the LED. But any attempt to pick up the key will not change the operating mode, but will cause the siren to turn on for 1 s.

The power supply unit of the device consists of a rectifier on a diode bridge VD3-VD6 (a step-down power transformer is not shown in the diagram) and two integral stabilizers DA1 and DA2. Diodes VD3-VD8 can be replaced by any diodes with a voltage of at least 50 V and a current of 1 A. The voltage of 13,7 V is designed to power the HA1 siren and recharge the battery that supports the operation of the device when the mains is turned off. If there is no need for backup power, instead of KR142EN8E, you can install a 12 V stabilizer, and exclude diodes VD7 and VD8.

Siren HA1 - automobile UP-35, but any other piezo sirens, for example, used in security systems (OOPZ-12, "Svirel"), can also be used. The storage battery is a maintenance-free acid battery designed for fire and security alarm devices.

The device is assembled on a printed circuit board made of one-sided foil fiberglass (Fig. 2).

(click to enlarge)

For the DD1 microcontroller, it is best to provide a panel. This will allow, if necessary, to replace or reprogram the microcontroller. The scheme of the programmer and the program for it can be found on the Internet. For example, at the address . There is also a programming manual.

To register the key, briefly close the contacts of the SA1 "PROG" switch. As soon as the HL1 LED lights up, touch the X1 contacts with the key. Successful registration will be confirmed by the LED going out and a short siren sound. After a while, the LED will light up again - the controller is ready to register the next key. There may be seven in total. The eighth will erase data about the first, the ninth - about the second, and so on in a circle. 40 seconds after the last registration, the device will automatically return to the operating mode.

To cancel the registration of all keys, it is enough to briefly close the SA2 "ERASE" switch. The memory will be cleared and the registration mode described above will be enabled. This procedure is necessary when you turn on the device for the first time, as well as if one of the keys is lost.

Assembler program text and controller firmware

Author: A. Voskoboynikov, Smolensk

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