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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Cell phone based car alarm. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms Among the numerous publications on the use of mobile cell phones to transmit an emergency signal of a protected object (car), it is not always possible to choose a suitable device for repetition due to its complexity or lack of necessary details, experience, etc. I propose a simple, easy-to-replicate design of an auto-guard, which works both independently and as a supplement to the regular car alarm. It will allow you to take appropriate measures in a timely manner to prevent, for example, the evacuation of a car or an attempted theft. First of all, the task was not to “get into” the electrical equipment of the car and not change anything in its design, for example, so that there would be no claims from dealers for a warranty case. In addition to a mobile phone, you will need two resistors, a capacitor, a relay, a transistor, a shock sensor from a car alarm, and a fused power plug for the cigarette lighter or auxiliary electrical outlet.
The diagram of the autoguard is shown in fig. 1. The device imitates pressing the button of a cell phone programmed in advance to a specific subscriber number. The author used a NOKIA 3310 phone. When the shock sensor is triggered, the negative terminal of capacitor C1 is briefly connected to a common wire, so the capacitor is charged. The transistor VT1 opens, the relay K1 is activated, and while the capacitor C1 is discharging, it is held in this state, closing the "1.1" button of the cell phone with its contacts K1. The "pressing" time can be increased if the capacitance of the capacitor C1 and the resistance of the resistor R1 are increased, and vice versa. Relay K1 - standard automobile 90.3747 of domestic production. The relay winding (contacts 86 and 85) is connected to the collector of the transistor VT1 and to a common wire, and contacts 30 and 87 - to the button "1" of the phone with two thin stranded wires, for example MGTF, through the slots in the side of the front panel of the phone. We will replace the KT973B transistor (without a heat sink) with a KT973A or an imported p-n-p composite structure with an allowable collector current that exceeds the maximum current through the relay winding. You can also use two conventional transistors by turning them on according to the Darlington circuit. If there is a relay of suitable sizes for an operating voltage of 12 V with a winding resistance of more than 500 ohms and normally open contacts, then instead of a transistor of the KT973 series, a low-power one will do, for example, from the KT3107 series with letter indices B, G, D, K. When using transistors of the n-p-n structure, it is necessary to change the polarity of connecting the capacitor, the shock sensor and the supply voltage. It is advisable to use a two-level shock sensor, i.e. with four leads: red (+12 V); black (common); blue/green - warning signal, not used; white - alarm. The color coding of the last pins may be different. It can be purchased at an auto accessories store or at the car market. Secure the sensor to the floor panel under the front passenger seat using double-sided tape. You can also use automotive sensors of volume, movement, both independently and by connecting them in parallel to the shock sensor. Of course, the phone requires periodic recharging of the battery. Therefore, it is desirable to integrate a car charger (charger) for cell phones into the design. Two of its input power wires in the appropriate polarity through the switch are also connected to the power plug.
The whole structure is located in the storage compartment on the center console under the armrest cover. The appearance of the guard with a charger in a case with the cover removed is shown in fig. 2, and all components - in Fig. 3.
The call number for the button is written to the phone from its menu in the following sequence: Menu > Messages > Set voice mailbox number (phone number to which the alarm will be sent) > Ok. To turn on the mounted autoguard, you need to insert the power plug into the cigarette lighter socket, turn on the cell phone and, after getting out of the car, close the door. If the shock sensor is set correctly on the control phone, the call will go through, which means that the car is in the cellular coverage area and, after the call is dropped, it is ready for work. Otherwise, adjust the sensitivity of the sensor. My Ford Focus 2 has been using this guard for over three years. For its installation and use in other car brands, where the +12 V voltage in the cigarette lighter socket is turned off when the ignition key is removed, the help of a specialist is required. You can combine turning on and off the standard alarm and this car guard from the standard alarm key fob, but here you can’t do without interfering with the car’s electrical equipment. Author: N. Mashonkin
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