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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Fisherman's echo sounder. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Home, household, hobby A block diagram explaining the design and operation of the echo sounder is shown in fig. one. The clock generator G1 controls the interaction of the device nodes and ensures its operation in automatic mode. The short (0,1 s) rectangular pulses of positive polarity generated by it are repeated every 10 s. With their front, these pulses set the digital counter PC1 to zero and close the receiver A2, making it insensitive to signals for the duration of the transmitter. The falling clock pulse triggers the transmitter A1, and the emitter-sensor BQ1 emits a short (40 μs) ultrasonic probing pulse towards the bottom. At the same time, the electronic key S1 is opened, and oscillations of the reference frequency of 7500 Hz from the generator G2 are fed to the digital counter PC1.
At the end of the transmitter, the receiver A2 opens and acquires normal sensitivity. The echo signal reflected from the bottom is received by the sensor BQ1 and, after amplification in the receiver, closes the key S1. The measurement is completed, and the indicators of the PC1 counter highlight the measured depth. The next clock pulse again translates the counter PC1 to the zero state, and the process repeats. A schematic diagram of an echo sounder with a depth measurement limit of up to 59,9 m is shown in fig. 2. Its transmitter is a push-pull generator based on transistors VT8, VT9 with a transformer T1 tuned to the operating frequency. The positive feedback necessary for self-excitation of the generator is created by the R19C9 and R20C11 circuits. The generator generates pulses with a duration of 40 μs with RF filling. The operation of the transmitter is controlled by a modulator consisting of a single vibrator based on transistors VT11, VT12, which forms a modulating pulse with a duration of 40 μs, and an amplifier based on a VT10 transistor. The modulator operates in standby mode, the triggering clock pulses come through the capacitor C14.
The echo sounder receiver is assembled according to the direct amplification scheme. Transistors VT1, VT2 amplify the echo signal received by the emitter-sensor BQ1, transistor VT3 is used in the amplitude detector, transistor VT4 amplifies the detected signal. A single vibrator is assembled on transistors VT5, VT6, which ensures the constancy of the parameters of the output pulses and the sensitivity threshold of the receiver. The receiver is protected from the transmitter pulse by a diode limiter (VD1, VD2) and a resistor R1. The receiver uses a forced shutdown of the receiver's single vibrator using the VT7 transistor. A positive clock pulse enters its base through the diode VD3 and charges the capacitor C8. Opening, the transistor VT7 connects the base of the transistor VT5 of the receiver's single vibrator to the positive power wire, thereby preventing it from being triggered by incoming pulses. At the end of the clock pulse, the capacitor C8 is discharged through the resistor R18, the transistor VT7 gradually closes, and the single-shot receiver acquires normal sensitivity. The digital part of the echo sounder is assembled on DD1-DD4 microcircuits. It includes a key on the element DD1.1, controlled by an RS flip-flop on the elements DD1.3, DD1.4. The counting start pulse is supplied to the trigger from the transmitter modulator through the VT16 transistor, the end pulse is from the receiver output through the VT15 transistor. The pulse generator with an exemplary repetition rate (7500 Hz) is assembled on the element DD1.2. A negative feedback circuit is made up of resistor R33 and coil L1, leading the element to a linear section of the characteristic. This creates the conditions for self-excitation at a frequency determined by the parameters of the L1C18 circuit. The generator is tuned exactly to the specified frequency with a coil trimmer. The reference frequency signal is fed through the key to a three-digit counter DD2-DD4. It is set to the zero state by the edge of the clock pulse coming through the VD4 diode to the R inputs of the microcircuits. The clock generator that controls the operation of the echo sounder is assembled on transistors of different structures VT13, VT14. The pulse repetition rate is determined by the time constant of the R28C15 circuit. The indicator cathodes HG1-HG3 are powered by a generator based on transistors VT17, VT18 [2]. Button SB1 ("Control") is used to test the device. When you press it, the VT15 key receives a closing pulse and the echo sounder indicators highlight a random number. After some time, the clock pulse switches the counter, and the indicators should show the number 888, which indicates that the echo sounder is working. The echo sounder is mounted in a box glued from high-impact polystyrene. Most of the parts are placed on three printed circuit boards made of foil fiberglass with a thickness of 1,5 mm. On one of them (Fig. 3) a transmitter is mounted, on the other (Fig. 4) - the receiver, on the third (Fig. 5 - digital part of the echo sounder. The boards are fixed on a duralumin plate with dimensions of 172x72 mm, inserted into the box cover. Holes for the Q1 (MT-1) power switch, SB1 (KM1-1) button and VR-74-F socket of the XI coaxial connector are drilled in the plate and cover, and a window for digital indicators is also cut out. The echo sounder uses MLT resistors, capacitors KLS, KTK and K53-1. Transistors KT312V and GT402I can be replaced with any other transistors of these series, MP42B - with MP25, KT315G-with KT315V. Chips of the K176 series are interchangeable with the corresponding analogs of the K561 series, instead of the K176IEZ (DD4) chip, you can use K176IE4. If the echo sounder will be used at a depth of no more than 10 m, the DD4 counter and the HG3 indicator can be omitted. The windings of the T1 transformer are wound with PELSHO 0,15 wire on a frame with a diameter of 8 mm with a ferrite (600NN) trimmer with a diameter of 6 mm. Winding length - 20 mm. Winding I contains 80 turns with a tap from the middle, winding II - 160 turns. The T2 transformer is made on a ferrite (3000NM) ring of size K16X10X4,5. Winding I contains 2X 180 turns of wire PEV-2, 0,12, winding 11-16 turns of wire PEV-2, 0,39. Coil L1 (1500 turns of wire PEV-2 0,07) is wound between the cheeks on a frame with a diameter of 6 mm made of organic glass. The diameter of the cheeks is 15, the distance between them is 9 mm. Trimmer - from the armored magnetic circuit SB-1a made of carbonyl iron. The ultrasonic emitter-sensor of the echo sounder is made on the basis of a round plate with a diameter of 40 and a thickness of 10 mm from barium titanate. Thin (0,2 mm in diameter) lead wires are soldered to its silver-plated planes with Wood's alloy. The sensor is assembled in an aluminum cup from an oxide capacitor with a diameter of 45 ... 50 mm (height - 23 ... 25 mm - is specified during assembly). In the center of the bottom of the glass, a hole is drilled for a fitting, through which a coaxial cable (RK-75-4-16, length 1 ... 2,5 m) will enter, connecting the sensor with the echo sounder. The sensor plate is glued with 88-N glue to a 10 mm thick soft microporous rubber disk. During installation, the cable braid is soldered to the fitting, the central conductor - to the output of the sensor lining glued to the rubber disk, the output of the other lining - to the cable braid. After that, the disk with the plate is pushed into the glass, passing the cable into the fitting hole, and the fitting is fixed with a nut. The surface of the titanium-nat plate should be deepened into the glass 2 mm below its edge. The glass is fixed strictly vertically and poured to the edge with epoxy. After the resin hardens, the sensor surface is ground with fine-grained sandpaper until a smooth plane is obtained. Solder the mating part of the XI connector to the free end of the cable. To establish an echo sounder, you need an oscilloscope, a digital frequency meter and a 9 V power supply. Turning on the power, check the operability of the counting device: if it is working, then the indicators should display the number 88,8. When you press the SB1 button, a random number should appear, which, with the arrival of the next clock pulse, should again be replaced by the number 88,8. Next, set up the transmitter. To do this, a sensor is connected to the echo sounder, and an oscilloscope operating in standby sweep mode is connected to winding 11 of transformer T1. On the screen of the oscilloscope with the arrival of each clock pulse, a pulse with RF filling should appear. The trimmer of the transformer T1 (if necessary, select the capacitor C10) achieve the maximum amplitude of the pulse, which should be at least 70 V. The next stage is the establishment of an exemplary frequency pulse generator. To do this, the frequency meter through a resistor with a resistance of 5,1 kOhm is connected to pin 4 of the DD1 microcircuit. At a frequency of 7500 Hz, the generator is tuned with a coil trimmer L1. If at the same time the trimmer takes a position far from the average, capacitor C18 is selected. The receiver (as well as the modulator) is best tuned for echoes as described in [I]. To do this, the sensor is attached with a rubber band to the end wall of a plastic box with dimensions of 300x100x100 mm (in order to eliminate the air gap between the sensor and the wall, it is lubricated with technical petroleum jelly). Then the box is filled with water, the VD3 diode is removed from the receiver and an oscilloscope is connected to the output of the receiver. The criterion for the correct setting of the receiver, transmitter modulator, as well as the quality of the ultrasonic sensor is the number of echo signals observed on the screen, resulting from multiple reflections of the ultrasonic pulse from the end walls of the box. To increase the visible number of pulses, resistors R2 and R7 are selected in the receiver, capacitor C13 in the transmitter modulator and the position of the trimmer of the transformer T1 is changed. To adjust the receiver turn-on delay device, the VD3 diode is soldered in place, the resistor R18 is replaced with a variable one (resistance 10 kOhm) and with its help the first two echo signals disappear on the oscilloscope screen. Having measured the resistance of the introduced part of the variable resistor, it is replaced by a constant of the same resistance. After tuning, the number of echo signals on the oscilloscope screen should be at least 20. To measure the depth of a reservoir, it is best to fix the sensor on a float so that its lower part is immersed in water by 10 ... 20 mm. You can attach the sensor to a pole, with which it is immersed in water for a short time, while measuring depth. When using the echo sounder in a flat-bottomed aluminum boat for measuring shallow depths (up to 2 m), the transducer can be glued to the bottom inside the boat. In conclusion, it should be noted that on sunny days the brightness of the digital indicators may be insufficient. It can be increased by replacing the Korund (Krona) battery with a power source with a slightly higher voltage, for example, a battery made up of eight D-0,25 batteries (this will not require any changes in the circuit and design of the device). Literature
Authors:V. Voitsekhovich, V. Fedorov; Publication: N. Bolshakov, rf.atnn.ru
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