Electronic call for a telephone on a microcircuit. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic call for a telephone on a microcircuit. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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The electrical circuit of the electronic call is shown in the figure.

Electronic call for a telephone on a microcircuit

A constant supply voltage within 11-29 V is supplied to the output of the internal power supply unit with hysteresis (pin 1). The useful output current of microcircuits is up to 35 mA at an output voltage of up to 17 V, which allows loading the microcircuit with low-power light and sound indicators without an additional current-amplifying cascade, as well as converting the output signal to control actuators. The load must have a resistance of at least 150 ohms.

The microcircuit contains two built-in AF generators and an output amplifier. One of the generators with an RC circuit connected to pins 3 and 4 generates pulses with a frequency of about 10 Hz. This signal is a control signal for another generator, the corresponding RC elements of which are connected to pins b and 7 of the microcircuit. The resulting amplified signal from the output of the microcircuit (pin 8) is fed to the load. The voltage to turn on the low-frequency generator is supplied to pin 2. Turning on this generator directly depends on the voltage value at pin 2, so you can control the operation of the entire node by changing the voltage amplitude. Thus, on the basis of DBL5001 and DBL5002 and similar microcircuits, parametric signaling devices with thermal and photo sensors, watchdogs, pulse generators and other simple multifunctional devices can be designed. And the electrical parameters make it possible to use these microcircuits in a variety of devices, despite the fact that they were specially developed for telephony.

In the absence of a call signal (and on-hook), the constant voltage in the telephone line is approximately 60 V. Capacitor C1 does not pass the constant component of the voltage, therefore, at pins 1 and 4 of the DA1 microcircuit, the supply voltage is zero. The sound capsule is not active. When you pick up the handset, the constant voltage in the telephone line drops to 3-6 V. When you make a call from the telephone line, an alternating voltage (about 60 V) passes through the capacitor C1, the limiting resistor R1, is rectified by the bridge diodes VD1-VD4 and goes to the DA1 chip - pins 1 and 4. Pin 4 is used to power the internal output amplifier of the microcircuit, which in this case turns on simultaneously with the power supply unit. Oxide capacitor C2 smooths out voltage ripples.

The capacitance of this capacitor is selected empirically. Its increase in this case is not recommended, otherwise, due to the accumulated charge on the C1 plates and the low current consumption of the DA1 chip, the generator will work and the HA1 capsule will emit an AF signal not only during intermittent phone calls, but constantly, that is, while the subscriber receives call. Through the limiting resistor R2, a constant voltage of 10-12 V is supplied to the control input of the low-frequency oscillation generator, and it, in turn, starts the second generator, the oscillation frequency of which is determined by the R4C4 elements. In this case, this frequency is about 800 Hz. The sound piezoelectric capsule HA1 turns on and emits an AF signal.

The circuit uses a sound capsule HA1 type HCM1206X. Instead, you can use any other piezoelectric or dynamic capsule with a resistance of at least 150 ohms. Instead of foreign microcircuits DBL5001 and DBL5002, domestic microcircuits KR1436AP1, EKR1436AP1 can be used in the circuit without any changes. These microcircuits can be used to repair imported SLTs, in which the call is implemented on DBL5001 and DBL5002 microcircuits. All fixed resistors in the circuit are of the MLT-0,25 type. Oxide capacitors - type K50-29 or similar. Non-polar capacitor C4 - type KM6 with a group of TKE H70 or similar. Capacitor C1 - type MBM, MBGO, K73-10 or similar for an operating voltage of at least 100 V.

Diodes VD1-VD4 can be used type KD103 or KD105 with any letter index.

The device does not need adjustment. Chip DA1 is powered directly from the telephone line (TL). Connection to the TL is carried out through a connector, for example RP2-5. The polarity of the connection in this case is not critical.

Author: Kashkarov A.P.

See other articles Section Telephony.

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