Stand for prototyping of radio-electronic devices. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Stand for prototyping of radio-electronic devices. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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One of the stages in the development of various electronic components is prototyping. In its process, the choice of active components is specified, their modes of operation are determined, the values of the elements are selected, electrical tests are carried out, etc. Currently, the so-called solderless breadboards are becoming more and more popular, which allow you to quickly (without soldering) assemble the device to be prototyped and carry out the necessary work to improve it.

However, for prototyping, in addition to such a board, you will also need power supplies, which, of course, you cannot do without, as well as some other devices - pulse generators of various shapes, a low-power ultrasonic frequency converter, a dynamic head, light indication elements, etc. If you combine these devices in one design, you get a convenient stand for prototyping various electronic devices. The description of just such a stand is offered to the attention of readers. Depending on the "specialization", it may include certain nodes.

Rice. 1 (click to enlarge)

The layout of the proposed stand is shown in fig. 1. It consists of a power supply, an ultrasonic frequency converter, a dynamic head, generators of rectangular and triangular pulses with various amplitudes, and a comparator with a light indication of the output level.

The proposed stand will allow you to quickly make prototyping of individual components of radio-electronic equipment: AF and HF amplifiers, detectors, generators, devices on transistors, analog, digital microcircuits and microcontrollers. A comparator with light indication will help to fix the moments of voltage change, check the voltage of logic levels, etc. The presence of RF and LF connectors will allow you to connect various measuring instruments or additional power supplies.

Using the stand, you can quickly check the health of microphones, including electret ones, since it has a power source and an ultrasonic frequency converter with a dynamic head. The presence of a rectangular pulse generator will allow you to check the performance of digital microcircuits of a small and medium degree of integration: logic elements, counters, registers, etc. Using this generator and an ultrasonic frequency converter, you can check the health of piezoelectric emitters, headphones, a triangular pulse generator and an oscilloscope to easily determine the moment the appearance of restrictions in various stages of AF amplifiers. There is no point in listing all possible options. Each radio amateur, in accordance with his needs, will be able to use such a device.

The power supply unit generates a stabilized regulated bipolar voltage of 2x(0...12) V at a load current of up to 0,4 A with short circuit protection and light and sound emergency alarm, as well as a fixed stabilized +5 V at a current of up to 0,4 A The power supply includes a step-down transformer T1, a bipolar rectifier on a diode bridge VD1, a voltage regulator of +5 V on an integrated regulator DA2, an adjustable voltage regulator of positive polarity 0.12 V on microcircuits DA1, DA3, transistors VT1, VT3, an optocoupler U1 and an adjustable stabilizer negative polarity on transistors VT2, VT4 and optocoupler U2. LED HL1 - stand indicator.

The adjustable voltage stabilizer of positive polarity is assembled according to a compensation scheme. Transistor VT1 - regulating, microcircuit parallel voltage regulator DA3 - control. Due to the fact that its output 2 is not connected to a common wire, but to a -2,5 V voltage regulator assembled on the DA1 chip, it turned out to be possible to regulate the output voltage (with resistor R10) in the range from 0 to 12 V. On the transistor VT3 and optocoupler U1 current protection is assembled, current sensor -

resistor R8. When the output current of the stabilizer reaches 0,4 A, the transistor VT3 will open and the voltage at the base of the regulating transistor VT1 will decrease, so the output current will be limited to the specified value. At the same time, the phototransistor of the optocoupler U1 will open, and the power supply will be supplied to the sound emitter HA1 with a built-in generator and the flashing LED HL2. The signaling devices for overloading the power supply by current will turn on - an intermittent sound signal will sound and the LED will flash.

Adjustable negative voltage stabilizer is "tied" to the output voltage of the positive polarity stabilizer. This binding is implemented using the DA4.1 op amp. When the voltage of the positive polarity changes, the negative voltage also changes. Current protection is assembled on transistor VT4 and optocoupler U2, current sensor - resistor R7. Therefore, the output voltage is regulated by one variable resistor R10, and when the current protection is triggered in one of the stabilizers, the output voltage decreases for both and light and sound signals are given. It should be noted that there is no overload indication in the +5 V voltage regulator, there the current is limited by the stabilizer microcircuit itself (DA2).

The generator of rectangular pulses with a repetition rate of 1 kHz and an amplitude of 5 V is assembled on a logic element DD1.1. From its output, the signal through the current-limiting resistor R26 is fed to the output socket XS6. Through another current-limiting resistor R20, it is fed to the base of the transistor VT5, and rectangular pulses are formed on its collector with the same frequency, but with an amplitude equal to the output voltage of the adjustable positive polarity stabilizer. These pulses are fed through the resistor R18 to the output socket XS5. An integrator is assembled on the op-amp DA4.2, which forms triangular-shaped pulses with an amplitude of 1 V from rectangular ones, which then arrive at the XS4 socket.

The voltage comparator is assembled on logic elements DD1.2, DD1.3, its input resistance is at least 500 kOhm, the resistor R14 sets its threshold in the range of 2,5 ... 12 V. When the input voltage (positive polarity) supplied to socket XS7, will exceed the set threshold, the HL3 LED will light up.

An UZCH is assembled on the DA5 chip, which can be used separately or connected to its output with a BA1 dynamic head. To do this, a plug is installed in the XS2 socket, in which contacts 1 and 4, as well as 2 and 3 are connected to each other. The input signal is fed to the XS3 socket, the volume is adjusted by a variable resistor R15. The dynamic head can also be used separately.

The device uses fixed resistors MLT, S2-23, variables - SP4-1, SPO, oxide capacitors - imported, the rest - ceramic K10-17. The switch is MT1, the transformer is TPP112-19 or another with a rated power of 7.10 W and two secondary windings of 11 V each with an output current of up to 0,4 A. Instead of the KTs407A diode bridge, separate rectifier diodes can be used, for example, 1N4001-1N4007. The device has sockets: XS1 - from the power cable of the drive, the rest - from the PBS, PBD series.

Rice. 2 (click to enlarge)

All elements are mounted on a printed circuit board made of fiberglass laminated on one side with a thickness of 2 mm from the side of the printed conductors, the drawing of which is shown in Fig. 2. For the dynamic head (it is located on the right side of the board), several dozen holes with a diameter of 2.3 mm are drilled (not shown in Fig. 2), they are sealed from the head installation side with a piece of thin fabric. The switch, variable resistors, sockets, fuse holder and LEDs are installed in the board holes. In addition, the transformer, dynamic head, acoustic emitter, all sockets and LEDs are glued to the board with hot glue.

The appearance of the stand is shown on the 1st p. covers. The board is fixed on a metal base (aluminum plate 2,3 mm thick) at an angle of 50.60° with the help of corners. The dimensions of the base depend on the type of solderless board used. The base is simultaneously used as a heat sink. Using screws, a DA2 chip is attached to it (directly) and transistors VT1, VT2 (through heat-conducting insulating gaskets). From the sides and back, the elements of the board are protected from mechanical influences by walls. Shock-absorbing "legs" are installed on the bottom side of the base. The solderless board can be attached to the base using sealant. On the sides of the base there are connectors for connecting measuring instruments, for example, bayonet sockets СР50-73Ф (BNC) and screw terminal blocks for external power supplies and other devices. The type and number of connectors can be chosen by the user.

Establishment begins with checking the performance of the power supply. The output voltage adjustment interval is set by a selection of resistors R4 (upper limit) and R9 (zero setting). In the case of excitation of an adjustable stabilizer of positive polarity, it is necessary to connect a ceramic capacitor with a capacity of 1 μF between pins 3 and 3 of the parallel stabilizer DA0,01 (it is marked C' on the printed circuit board drawing). The frequency of the rectangular pulse generator is set by selecting resistor R22, and resistor R24 - the amplitude of the triangular voltage. Handles with pointers are installed on the engines of variable resistors and provided with scales.

Attention! Solderless boards are not designed to operate on a 220 V network.

Author: I. Nechaev

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