Electronic turn signal switch. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic turn signal switch. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The currently most common electromechanical turn signal interrupter for a car has a number of disadvantages - low reliability due to erosion and oxidation of contacts, insufficient mechanical strength of the heated thread, a change in switching frequency due to a gradual change in the characteristics of the thread and spring, and also due to voltage fluctuations of the on-board network . Therefore, many different electronic circuit breakers have been developed by car and radio amateurs with better reliability and stability. Of the wide variety of such breakers, the most acceptable are designs with a non-contact (electronic) switch of signal lamps and an autonomous stabilized power supply to the generator - the switching cycle sensor.

The performance of such interrupters is significantly increased if their circuit provides for the use of a pilot lamp, which allows timely detection of malfunctions of signal lamps and the interrupter itself. This article describes a turn signal breaker that meets these requirements. The breaker is designed for a three-point connection to the alarm system (that is, it does not require a paired switch), is non-contact, provides high switching frequency stability in a wide range of on-board voltage changes and, in addition, is equipped with a sound generator that acts as an additional signal switching control channel turn. This design completely replaces the thermoelectromagnetic interrupter of the VAZ-2101 car and can also be used on cars of other brands.

Schematic diagram of the interrupter is shown in fig. one.

Electronic turn signal interrupter
Ris.1

As can be seen from the figure, the interrupter consists of a switching time cycle sensor, made on three 2I-NOT logic elements (DD1.1 - DD1.3) according to the principle of a self-oscillating multivibrator [1], a buffer stage (DD1.4), a current amplifier (VT1 ) and a powerful transistor key (VT2), the load of which is the signal lamps of the car. The multivibrator is powered by a voltage stabilized using a VD2 zener diode. In this case, the power source is the capacitor C2, which is charged through the diode VD1 with each cycle of turning on the signal lamps. Blocking this diode during periods when the transistor switch is closed (voltage is not applied to the signal lamps) prevents this capacitor from discharging. The energy accumulated by the capacitor is quite enough to power the DD1 (K176LA7) microcircuit. Thus, the time cycle sensor makes it possible to ensure the stability of the switching frequency of the interrupter without the use of a paired switch, which is usually used in order to supply power to the electronic switching rhythm sensor from the on-board network through one of the two pairs of contacts, regardless of the signal lamp power supply circuit.

To ensure the operation of the control lamp for turning on the turn signal, the emitter of the transistor key VT2 is connected to a power source through resistor R5. The voltage drop across it controls the work of the triode VT3, the load of which is the control lamp HL1. With a good signaling circuit, the control lamp is on during periods when the transistor key is open. When the load of this key changes, caused by an open in the signaling circuit or a burnout of at least one signal lamp, the current through the resistor R5 decreases and the voltage drop across it is insufficient to open the VT3 triode, as a result of which the control lamp does not light.

On the DD2 (K176LA7) chip, a sound generator is assembled, made, like the switching cycle sensor, according to the principle of a self-oscillating multivibrator. The sound generator signal is fed to an amplifier (transistor VT4), the load of which is the handset capsule VA. VT2 is locked). The use of a powerful GT1V transistor as a switch for signal lamps VT8 (admissible direct collector current 2 A) makes it possible to use this breaker not only for normal, but also for emergency signaling, when the load on the output stage increases significantly.

Structurally, the interrupter is assembled on a round circuit board with a diameter of 50 mm. This board contains all its parts, with the exception of the output transistor VT2, which is mounted on a cooling radiator, which is attached to the circuit board with standoff screws. The circuit board together with the radiator is placed in a metal case made in the form of a duralumin sleeve. At the bottom of this sleeve, an insulating gasket made of fluoroplastic with a centering groove made according to the outer size of the radiator is installed. Thanks to this gasket, the radiator is fixed coaxially with the body.

See other articles Section Automobile. Electronic devices.

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