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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Signaling device on the K157XA2 chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur [an error occurred while processing this directive] Typically, a sound signaling device with a periodically changing tone of sound (siren) is made on the basis of two multivibrators, one of which generates the main tone of the audio frequency, the second switches frequency-setting RC chains with a certain periodicity. Generators are assembled either on separate amplifying elements (most often two transistors) or on logic microcircuits. The latter option is both simpler and more economical. However, this kind of device can also be built on the widely used analog K157XA2 microcircuit, designed to amplify and detect intermediate frequency signals with amplitude modulation in radio receivers. Contained "inside" the microcircuit, two amplifiers are interconnected by a transistor, providing AGC in the traditional use of the microcircuit as an IF amplifier. The degree of this connection is regulated by the built-in DC amplifier (pin 12). Using this structure, an audio frequency generator with a periodically changing tone was built (Fig. 1).
The input of the first amplifier (pin 1) is closed through the capacitor C1 to a common wire (it is possible to add a resistor Rd with a resistance of 10 ... 100 Ohm, shown by a dashed line). Experiments have shown that the fundamental tone of the audio frequency directly depends on the capacitance of this capacitor, which can be changed from 0,033 to 0,33 microfarads. The output of the first amplifier (pin 14) is connected to the input of the second one (pin 5) through the capacitor C3. By selecting the resistor R1, the required gain of the entire signal path is set. The selection of capacitor C2 regulates the feedback coefficient of the second amplifier for alternating current. The feedback necessary to excite the amplifier at an audio frequency is provided by a tuning resistor R2, by adjusting which the desired frequency of the output signal tone change is achieved. The output of the generator (pin 10) through the capacitor C5 is loaded on the resistor R3, from which the signal is taken for subsequent amplification. The ultrasonic frequency converter is assembled according to the simplest scheme on a part of the K174XA10 microcircuit and provides an output power of up to 9,5 W with a supply voltage of 8 V and a load resistance of 0,5 ohms. During prototype tests of the signaling device, the high-frequency dynamic head 2GD36 emitted rather loud howling and piercingly unpleasant sounds, which, in fact, is required from a siren. You can generally do without UZCH, greatly simplifying the device. Connected instead of resistor R3, a small head with a resistance of 50 ohms reproduced sounds similar to the crying of a child with sufficient volume, which suggests using the device as part of an "electronic nanny". The ability of the device to "create" a wide variety of sounds with a simple combination of capacitors C1, C4 and R3 adjustment, small dimensions and economy allow it to find a variety of applications. The device connected through a reed switch with a magnet will serve as a signaling device for a loosely closed door. It can be part of a kitchen timer. In these cases, it is permissible to power the signaling device from a battery with an EMF of about 6 V. The voltage stabilizer elements are excluded from the circuit (DA3, VT1, C8, C9, R4 and VD1), and the positive terminal of the battery is connected through the switch contacts to terminals 11 and 13 of the DA1 and DA2 respectively. The author used a signaling device in the car so as not to leave it for an "overnight" with the parking lights on (damage to the battery as a result of such forgetfulness is guaranteed). To adapt the signaling device for power supply from a car battery, a voltage stabilizer (VT1, VD1, R4 and C9) has been introduced, which limits the supply voltage DA2 to 9 ... when the generator is running up to 10 ... 174 V, the internal stabilizer of the microcircuit will be disabled. The supply voltage to the DA10 chip, equal to 14 ... 15 V, is supplied through the integrated stabilizer DA1. To provide the necessary logic for turning on the signaling device under two specified conditions (enabled "dimensions" and an open driver's door), an electronic key on a VT2 transistor was used (Fig. 2).
SF1 is a switch mounted on the driver's door (available in the car); SA1 - side signal switch. When the driver's door is closed and the "dimensions" are turned off, the switches SF1 and SA1 are in the position shown in Fig. 2. When SA1 is turned on ("dimensions" are on), plus power is supplied to the signaling device, but it does not work, as it is disconnected from the "ground" "car (power minus) with a closed transistor VT2, the base of which is connected to the emitter through the filament of the interior lighting lamp HL1. When the driver exits the car, voltage is applied to the HL1 lamp through the SF1 contacts. It opens the transistor VT5 through the resistor R2, its resistance decreases sharply, which allows the signaling device to work, reminding the driver of the side lights on. Resistor R6 is necessary so that the base of the transistor VT2 remains connected to the emitter in the event of a burnout of the HL1 lamp. The whole structure is assembled in the body of the children's set "Youth" KP101. The dynamic head from the kit has been replaced with a more powerful imported 8 ohm impedance and suitable size. Elements of the signaling device are mounted on a board with dimensions of 100x60 mm. Transistors VT1 and VT2 are equipped with 10x15 mm aluminum angle heat sinks. The signaling device is not critical to the selection of parts. The DA3 chip is interchangeable with any domestic stabilizer with an output voltage of 4 ... 6 V. In extreme cases, you can assemble the stabilizer on individual elements according to the stabilizer circuit on the VT1 transistor, using the KS156A zener diode and the KT315G transistor for this. All resistors are MLT. KT815 transistors are suitable with any letter index. Zener diode VD1 - with the index B, C, G or the previous release -D811. Setting up the device, with known good parts, comes down to selecting the desired sound by adjusting R2 and the volume by adjusting R3. Author: V.Markov, village of Tuloma, Murmansk region.
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