Light and sound probe. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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In the article by A. Chanturia "Universal probes", published in "Radio" No. 12, 1986, very good, in the opinion of our permanent author I. Potanin, devices were described. Several instances of similar devices repeated by him, made according to the scheme of Fig. 1 of the mentioned article, work regularly with his friends. Deciding to improve their consumer properties, I. Potachin introduced additional phase voltage indicators on a neon lamp into the probes and an audible signaling of the results of continuity of the tested circuits. This is discussed in the article below.

The scheme of the modified probe is shown in fig. 1. All three of his DC amplifiers are assembled on discrete transistors: VT1, VT2; VT5, VT6; VT9, VT10. A neon lamp HL7 is additionally connected to the input of the device through a quenching resistor R4, which lights up when the XP1 probe is connected to the phase wire and the E1 sensor is touched by hand. On transistors VT3. VT4 assembled the simplest sound signaling device that works on an emitter in the form of a miniature BF1 headphone. Transistor VT8 controls the sound alarm.

In the upper position of the movable contact of the SA1 switch according to the diagram, this transistor is closed, the transistors VT3 and VT4 are not powered, and there is no sound alarm when the circuits are continuity. In the lower position of this contact, the base of the transistor VT8 is connected to the collector of the transistor VT5. Now the continuity of the chains will be accompanied not only by the lighting of the HL2 LED. but also by the beep of the BF1 phone. Moreover, the phone will sound at any resistance of the circuit under test, not exceeding 100 kOhm (with increasing resistance, the level and tone of the sound signal change).

The probe is powered by two "AA" ("316") galvanic cells with a total voltage of 3 V. There is no power switch, as in the original version. To reduce the threshold for determining the presence of a voltage of negative polarity to 7 ... 8 V, instead of the pn junction of the transistor VT7, it is permissible to turn on the zener diode VD5 (Fig. 1). but in this case, you will need to insert an additional power switch into the device.

The probe works as follows. When the XP1 and XP2 probes are closed, the battery voltage of +3 V through the resistors R8 and R6 enters the base of the transistor VT6 and opens it and the transistor VT5. The red LED HL2 will light up and will glow until the resistance of the circuit connected between the probes reaches 100 kOhm, however, with an increase in the resistance of the circuit under test, the brightness of the LED will decrease. The polarity of the tested voltage is determined on the XP1 probe relative to the XP2 probe (1). which in this case plays the role of a common wire. When a positive voltage of 1 ... 1 V is applied to the XP300 probe, transistors VT9 open. VT10 and the ML3 ("+") LED lights up with a yellow glow. If a negative voltage of 1 ... 10 V is applied to the XP300 probe, transistors VT2 will open. VT1 and the HL1 ("-") LED will light up with a green glow. When dialing diodes, pn junctions of transistors and oxide capacitors, it should be taken into account that there is a constant voltage on the probe probes, the polarity of which corresponds to the polarity indicated next to them XP1- ("-") and XP2- ("+").

In the probe, you can use low-power transistors with any letter index: silicon KT315, KT3102 (VT1, VT5-VT7, VT9. VT10): KT361. KT3107 (VT2. VT8) and germanium MP39-MP42 (VT3) and MP35-ML38 (VT4). Diodes VD1-V04 (KD521. KD522). HL1-HL3 LEDs are any of the AL307 series, preferably with a different glow color. It is recommended to choose a VD5 zener diode with a minimum stabilization voltage, for example. KS133A. KS133G. KS433A. KS139A. KS139G Neon lamp HL4 - any miniature, but also suitable from the LDS starter. Switch SA1 - miniature, for example. PD-9-2. Sound emitter BF1 - TM-4 headphone or a miniature electromagnetic emitter from domestic and imported desktop or wall clocks.

Most of the probe parts are mounted on the printed circuit board shown in fig. 2.

The entire structure is placed in a self-made case made of foil fiberglass with dimensions of 110x32x17 mm (Fig. 3).

The BF1 headphone and HL4 neon lamp are glued to the inside of the case's front panel. The SA1 switch is soldered to the foil side of the case. The F1 sensor is made in the form of a small bolt (MZ or M4) with a flat head, fixed on the side wall of the housing on the right. A mounting tab is placed under the bolt nut, to which the output from the HL4 neon lamp is soldered. Remove the foil around the sensor first. This must be done so that the HL4 lamp lights up only when the sensor is touched. Probe XP1 is a pin from the plug. The XP2 is made from a short felt-tip pen that can be attached to a crocodile clip.

In conclusion, I would like to draw the attention of readers to the wide scope of the described probe. It allows you to determine the presence of alternating and direct voltage and judge the polarity of the latter, provides continuity of mounting circuits, cables, incandescent lamps, relays and semiconductor devices. With a certain skill, using this device, you can check the health of the capacitors and set their approximate capacitance in the range from 1000 pF to 1000 microfarads. True, with a low capacitance, the HL2 LED flashes for a very short time, but its glow is quite distinguishable. This operation is facilitated by an audible alarm.

And finally, since the probe makes it possible to detect a positive voltage from a value of about 1 V, it can be used to set the degree of discharge of galvanic cells with a voltage of 1.5 V. With a fresh element (the voltage on it is 2 V), the HL1 ("+") LED will light up with a yellow glow. If the voltage on the element under test fell below 1 ... 1,5 V. then a weak glow of the HL3 LED ("1,3") will also appear. With a deeper discharge, the brightness of the HL1.2 LED increases, and HL2 decreases, and at the same time, an audible signal is turned on, indicating that the element is discharged to a voltage of less than 0 V.

Author: I.Potachin, Fokino, Bryansk region

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