Call signal booster. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Call signal booster. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In some cases, the volume of the ringtone of a regular or cell phone, alarm clock, etc. may not be sufficient. In this case, the proposed device will help, which increases the volume of the call signal.

A diagram of such a device is shown in Fig.1. It includes a microphone amplifier based on a VT1 transistor, the supply voltage of which is stabilized by an integrated stabilizer on the DA1 chip. A voltage comparator is assembled on the operational amplifier (op-amp) DA2, and an electronic key is assembled on the transistor VT2.

Call signal booster

The BM1 microphone is placed in close proximity to the source of the sound signal. The output of the microphone amplifier is connected to the inverting input of the op-amp DA2. A constant voltage is supplied to the non-inverting input through the low-pass filter R4C3 from the engine of the resistor R3. Since it is greater than on the inverting one, the output of the op-amp will have a voltage close to the supply voltage. Transistor VT2 is closed because there is no bias voltage at the base. In this state, the device consumes a current of approximately 2,5 mA.

As soon as the call signal sounds, it will amplified and go to the inverting input of the op-amp. When the voltage on it equals the voltage at the non-inverting input, a pulse will appear at the output of the op-amp, which will go to the transistor. It will open, an acoustic signal will be heard from the dynamic head. At the next call signal, the process will be repeated. The device does not amplify all the signals coming to the microphone, but only those exceeding a certain level set by the resistor R3. This ensures the immunity of the device.

Most of the parts, except for the microphone and dynamic head, are placed on a printed circuit board (Fig. 2, 3) made of one-sided foil fiberglass.

Call signal booster

In addition to those indicated in the diagram, the device can use the KR1157EN502A, KR1157EN502B (DA1), K140UD6 (DA2) microcircuits, any transistors from the KT312, KT315, KT3102 (VT1), KT973 (VT2) series. Microphone - electret, for example, MKE-377, MKE-332, it is connected to the board with a shielded wire. The dynamic head can be from 2 W, with a voice coil resistance of at least 10 ohms. Capacitors - K50-6, K50-35 or similar imported ones, trimming resistor - SPZ-19, constants - MSC C2-33.

For the convenience of mounting a microphone on the body of a telephone, including a cellular phone, or an alarm clock, it must be placed in a small case equipped with a strap or rubber band. To exclude acoustic coupling between the microphone and the dynamic head, they should be separated in space.

The device must be powered from a 9...12 V source providing a maximum load current of 300...500 mA. It can be a battery of galvanic cells or a power supply unit.

Establishing the device comes down to setting its sensitivity with a tuning resistor R3.

Author: I. Nechaev, Kursk

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