Simple auto attendant. Free Technical Library article

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Simple car attendant

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Encyclopedia of radio electronics and electrical engineering / Automobile. Security devices and alarms

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At a supply voltage of 12...14 V, the device consumes a current of no more than 180 μA from the battery in standby mode.

The scheme of the autoguard is shown in fig. 1. After turning on the power with the SA1 toggle switch, voltage is supplied to the watchdog nodes and the slow charging of the capacitor C6 through the resistor R11 begins. At this time, the output of the inverter DD1.4 is low, the capacitors C3 and C4 are discharged. There is a time delay during which the owner of the car can leave the passenger compartment and close the door behind him. After a period of time equal to = 0,7 * R11 * C6 (time is in seconds, if the resistance is in megaohms, and the capacitance is in microfarads), a high level will be set at the output of the DD1.4 inverter and the watchman will go into standby mode.

(click to enlarge)

If you now open the trunk lid or the hood, the contacts SF1 or SF2 will close, a high level will appear at the output of the inverter DD1.1 and the capacitor C4 will start charging through the resistor R6 and the diode VD5, as well as the capacitor C3 through the diode VD8. Turning on the ignition will also charge these capacitors; this will open the transistor VT1, providing a low level at the input of the inverter DD1.1.

After a short time, the capacitors C3 and C4 will be charged and the output of the inverter DD1.3 will go low. With the pulse repetition rate of the generator (1 ... 2 Hz), the transistor VT2 begins to open, switching the car horn relay circuit. Audible alarms are heard, which repeat for a time of about 0,7*R9*SZ. After that, the watchman switches back to standby mode.

With the hood or trunk open, with the ignition on, alarm signals are given until either the watchman is de-energized by the SA1 toggle switch, or the hood, trunk lid are closed and the ignition is turned off.

If the door of the passenger compartment of the car is opened in the standby mode, the capacitor C0,7 will quickly charge, and after a time of 10 * R4 * C7 (usually 12 ... 4 s) and the capacitor CXNUMX. During this period of time, the watchman must be turned off, otherwise an alarm will sound. All time delays can be changed by appropriate selection of the values of the timing circuits.

The C2R14VD10C7 node is used to smooth out voltage surges in the on-board network that exceed 15 V and to protect against interference. Diode VD1 protects the transistor VT2 from self-induction voltage surges that may occur on the winding of the horn relay. The diode is soldered to the terminals of this relay.

The details of the guard are mounted on a printed circuit board made of foil fiberglass with a thickness of 1,5 mm. The board drawing is shown in fig. 2. The device uses resistors MLT, S2-33. Capacitors K50-16, K50-35 (oxide), KM-6, K73-17 (others). The use of oxide capacitors K50-6 is highly undesirable due to their high leakage current and too little reliability.

Simple auto attendant. PCB and parts layout

Diodes VD2, VD4-VD9 can be any silicon; VD3 - any one that can withstand a direct current of at least 0,3 A (for example, from the KD208, KD209 series). Diode VD1 is better to choose a pulse from the series KD521, KD522. Instead of KT3102EM, any transistor from the KT3102, KT342 series or KT315B, KT315G, KT315E transistors can be used in the watchdog; instead of KT829A - any of the KT829, KT972 series or a composite of KT315 and KT817 with any letter indices.

Chip K561LN2 can be replaced by KR1561LN2 or 564LN2 with some board correction. As an extreme case, you can use two K176LA7 microcircuits, but you will have to seriously change the pattern of printed conductors on the board, and also replace the KS215Zh zener diode with another one, for a voltage of 8 ... parallel.

The points on the board, numbered from 1 to 8, are connected by wires to the corresponding pins of the X1 connector. Connector X1 - MPN-8-1 or another with the required number of contacts.

Author: A. German, Radio No. 4 1993; Publication: cxem.net

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