Universal probe powered by ionistr. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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Galvanic cells or batteries, usually used for self-powered measuring instruments, have an alternative in the form of an ionistor - a capacitor that has a very high capacitance with small dimensions. The author skillfully took advantage of this in the new design of the probe.

When the probe is used infrequently, the batteries expire before the probe is needed again. This situation will not arise if capacitors with a double electric layer - ionistors are used for power supply [1,2]. One or two minutes is enough to charge such a capacitor, and the probe is ready for use. And it can work for quite a long time.

A probe with such an energy storage device allows you to "diagnose" electrical circuits, test diodes and other devices with pn junctions. The built-in pulse generator allows you to check the low-frequency and high-frequency circuits and nodes of various electronic equipment.

The probe circuit is shown in fig. 1. Its basis is a pulse signal generator based on transistors VT2, VT3, connected to an acoustic emitter or trimmer resistor R2. The field-effect transistor VT1 works in the charging device of the ionistor C4, and VT4 controls the operation of the generator.

The probe works as follows. The installation of the main modes is carried out by the switch SA1. In the "dialing" mode (checking the resistance of the circuit), when the switch SA2 is in position 4 ("Probe"), the controlled circuit is connected to the source of the transistor VT1 and the common wire using pins X2 and X4. If the resistance of this circuit is more than 1 kOhm, the current through the field-effect transistor is less than the threshold level and therefore the transistor VT3 remains closed and the generator does not work. When the resistance is less than this value, then VT3 opens and the sound signal of the generator indicates that the resistance of the circuit is less than 1 kOhm.

In the mode of checking pn junctions set by the switch SA1, the pin X1 is connected through the resistor R10 to the base of the transistor VT6. If the pn junction is working, then if it is connected by the anode to X1 and the cathode to X2, a direct current flows through it; transistors VT4-VT6 are open and the generator is running. When the transition is turned on in reverse polarity, a very small reverse current flows through it, VT6 is closed, there is no sound signal.

The generator generates pulses continuously when the SA2 switch is set to the "Gen." position. Its signal from the engine of the resistor R2 through the capacitor C3 goes to X1 without limiting the spectrum (in the "SHP" mode) or through the capacitor C2 (in the "HF" mode). The generator generates short pulses with a duration of about 30 μs and a repetition period of 1 ... 1,5 ms, having a wide frequency spectrum, which allows it to be used to test LF and HF stages. The amplitude of the signal can be adjusted by the trimmer resistor R2.

The charging mode of the ionistor C4 is provided by the elements VD1, VD2, HL1, VT1. After setting the switch SA1 to the "Charging" position and SA2 to the "Probe" position, the pins X1, X2 are supplied with a constant (plus on X1) or alternating voltage of 5 ... as well as AC rectification. VT20 acts as a current stabilizer, and HL2 as a charging indicator.

How is charging done? After applying voltage to the pins X1, X2, a current of about 10 mA, stabilized by the transistor VT1, flows through the diode VD1 and the ionistor. As it charges, the voltage on it grows, and when it reaches about 1,5 V, part of the current will begin to flow through the resistor R1 and the HL1 LED. By selecting a resistor R1 on the R1HL1 circuit, a voltage of about 3,2 V is set so that the ionistor is charged to a voltage of 2,5 V. The duration of this process is only 1 ... 2 minutes. There is no special power switch, since when SA2 is switched to the "Probe" position and X1 and X2 are open, only the reverse currents of the transistors and the self-discharge current C4 flow.

About Probe Design. Most of the parts are placed on both sides of a printed circuit board made of double-sided foil fiberglass; its sketch is shown in Fig. 2.

Capacitors C2 and C3 are installed on terminals SA1. Switches, an LED, and an acoustic emitter are fixed on the walls of the probe case, which can be an aluminum cylinder from a felt-tip pen or marker with an outer diameter of about 22 mm (Fig. 3). The printed circuit board is inserted into it with little effort.

The following details can be used in the probe: transistor VT1 - KP302A, KP303E or KP307A with an initial drain current of 10 ... 15 mA, VT4 - KP303A, KP303B with an initial drain current of about 1 mA. Transistors VT2, VT5 - series KT315, KT3102, VT3, VT6 - KT361, KT3107 with any letter index and h21E at least 50. Diodes VD1, VD2 - KD103A, KD104A, LED can be any of the AL307, AL341 series. Trimmer resistors - SP3-19a, constants - MLT, S2-33, R1-12. Ionistor C4 - K58-9a or K58-3; capacitor C1 - with a low leakage current K52, K53; C2, C3 - KM, K10-17. Switch SA1 - slide switch for five positions, for example, from network adapters, SA2 - any small switch for two positions and two directions.

Emitter VA1 - a capsule from small-sized headphones with a resistance of at least 100 ohms. It is permissible to replace the dynamic emitter with a piezoelectric one, for example, ZP-1, ZP-3 and similar ones, while the efficiency of the probe will increase, but the dimensions will have to be increased. In this case, a resistor with a resistance of 1 ... 3 kOhm is installed in parallel with the VA5 emitter.

In the author's version of the probe, the full charge of the ionistor was enough for 25 minutes of continuous operation of the generator, therefore, in the "dialing" mode or checking pn junctions, when the generator is turned on for a short time, its charge will be enough for a working day. In generator mode, efficiency can be improved by using a self-resetting button as SA2. In this case, it is briefly pressed after connecting X1 to the circuit under study.

Establishing the device is reduced to adjusting the threshold of the generator operation with resistor R5 so that at a supply voltage of 1,5 ... 2,5 V it works stably when a resistance of less than one kiloohm is connected to X1 and X2, and generation does not occur with a higher resistance. The oscillation frequency of the generator can be changed by selecting capacitor C5. In the diode test mode, you may need to select the resistor R9 to obtain stable operation of the probe at a reduced voltage (about 1,5 V).

So that when charging the ionistor, the voltage on it does not exceed 2,5 V, the resistance of the resistor R1 is selected, temporarily replacing it with a tuning resistor of 150 ohms. By setting R1 to the position of minimum resistance, connect X1, X2 to a power source with a voltage of 8 ... 10 V. Two to three minutes after the charging current is applied, the voltage on the supercapacitor is controlled and gradually, over several minutes, increase the resistance of the resistor until , until the voltage across the ionistor reaches 2,5 V. After that, the tuning resistor is replaced with a constant of the same resistance. In order not to make such a selection, the resistor R1 can be replaced by two low-power silicon diodes connected in series, for example KD103A. At a supply voltage of 1,5 V or less, the generator frequency decreases markedly, which indicates the need to recharge the supercapacitor.

If there is no ionistor, it will be replaced by a galvanic cell, for example, lithium with a voltage of 3 V, while all the parts that provided charging of the ionistor are excluded. If it is replaced with small-sized batteries, for example, D-0,03 (2 pcs.), The circuit is not changed, but it will be necessary to select a VT1 transistor with an initial current of 3 ... 5 mA and charge the batteries for 12 ... 15 h.

If you want the sound signal to sound constantly in the generator mode, switch SA2.1 is excluded, the collector of the transistor VT2 is connected to the lower (according to the circuit) terminals R2 and BA1, and the resistance R2 is increased to 1 kOhm.

Literature

1. Gailish E. et al. Ionistors KI1-1. - Radio, 1978, No. 5, p. 59.
2. Astakhov A. et al. Capacitors with a double electric layer. - Radio, 1997, No. 3, 4, p. 57

Author: I. Nechaev, Kursk

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