Sound indicator of ultrasound. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Indicators, detectors

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Ultrasounds surround us everywhere, it can be the "negotiations" of animals, the noise of various equipment, as well as ultrasounds specially generated by echo sounders, medical devices. Unlike sounds in the audible range, ultrasounds act on us imperceptibly. And not always favorable. A good example is that in a certain place, for example, near some kind of unit, you have a headache, and your hearing is somehow reduced. All symptoms of stun, but silence around. Seeming silence. "Decibels" of the ultrasonic range press on your ears, they deafen you, but you cannot understand this, because you do not hear the acoustic vibrations that disturb you.

Using this simple device, you can not only determine the source of ultrasound and its intensity, but also "listen" to ultrasound, determine the nature of its sound (intermittent, with varying frequency, etc.).

The basis of the device is an ultrasonic microphone MA40B8R (M1). The number "40" in its name refers to the frequency (40 kHz) at which it has maximum sensitivity. Below 32 kHz, the sensitivity drops sharply (-90dB). This sensitivity characteristic makes it possible to use it for monitoring ultrasound without the use of special filters that suppress sound frequencies.

The ultrasonic level indicator circuit consists of a microphone M1, a two-stage amplifier on transistors VT1 and VT2 and an AC voltage meter on diodes VD1, VD2 and a pointer indicator MA. An alternating voltage with Ml through the sensitivity regulator R7 is fed to a two-stage amplifier. Then the amplified AC voltage is detected by the diodes VD1 and VD2. A constant voltage is formed on the capacitor C6, proportional to the volume level of the ultrasound. This voltage is indicated by the MA pointer device.

Rice. 1 (click to enlarge)

To listen to ultrasound, the method of lowering its frequency to the frequencies of the sound range is used by dividing it with a digital counter.

From the collector VT2, an alternating voltage of ultrasonic frequency is supplied to the pulse shaper on the transistor VT3. The transistor is turned on without bias at the base and opens like an avalanche when the amplitude of the alternating voltage at its base exceeds the opening barrier of the transistor.

The pulses from the collector VT3 are fed to the counting input of the binary counter D1. The counter divides their frequency by 128. Then, from the output of the counter, the pulses are sent to the headphones.

As a result, for example, 40 kHz ultrasound is reproduced by headphones as a sound with a frequency of 312,5 Hz (40/128=0,3125). Now we can "hear" the ultrasounds, follow the change in their frequency, and determine their intensity by the arrow indicator. The disadvantage is that the volume of the sound in the headphones does not depend on the volume of the ultrasound, but this is compensated by the arrow level indicator.

Most of the parts are installed on a fiberglass printed circuit board with one-sided foil. The board is placed in a plastic case and is located along it. Next to it, in a hole specially sawn in the case, an imported dial indicator (similar to the M470 indicator) with the end position of the scale is installed. The total deflection current of the indicator arrow is 300mA, and the resistance is 1200 ohms. However, you can use any similar microammeter, with a scale of no more than 400mA and a resistance of at least 300 ohms. You can adjust its sensitivity by connecting an additional resistor in series, the resistance of which will need to be selected empirically.

The K561IE20 chip can be replaced with a K561IE16 counter. At the same time, the output will be not the 4th, but the 6th output of the microcircuit (you need to slightly change the printing of the board).

The power switch is a micro toggle switch mounted by soldering on the board. At the same time, the nut for fastening the toggle switch to the panel serves as an element for fastening the board in the case. Connector X1 is a socket for small-sized head stereo telephones, it is also installed on the board. The connection scheme of this connector is such that the headphones work connected in series.

The power source is a battery "Krona" with a voltage of 9V.

The tuned resistor R7 can be replaced with a variable one, then it will be possible to adjust the sensitivity of the device over a wide range.
The board print pattern and wiring diagram are shown in Figure 2, and Figure 3 shows how the parts of the device are placed in the case.

Rice. 2. PCB

Rice. 3. Wiring diagram

Rice. 4. Layout

Amplifying stages on transistors VT1 and VT2 need to be adjusted. By setting the tuned resistor to the position of minimum sensitivity (the slider is down to the end, according to the diagram), you need to measure the constant voltages on the collectors VT1 and VT2. If these voltages go beyond 2,5-3V, you need to select the resistance of the base resistors (R1 and R2, respectively).

The overall sensitivity is set by the trimming resistor R7 (initially it can be set to the maximum sensitivity position, up the circuit).

If it turns out that the device starts to sound only when the microammeter shows a level close to the maximum, you need to lower the sensitivity of the microammeter so that the beginning of the sound falls on the first third of its scale.

You can test the device by recording ultrasounds, for example, emitted by an ultrasonic washing machine or a device for repelling rodents.

The tone of the sound can be doubled if you take impulses to the headphones not from the 64th output of the counter, but from the 32nd.

Author: Lyzhin R.

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