Probe with acoustic and light indication. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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The proposed probe is used in the verification and adjustment of various electronic equipment. With its help, you can quickly check the integrity of the windings of relays, transformers, the serviceability of such radio elements as diodes, LEDs, transistors, capacitors, and evaluate the resistance of resistors. It has acoustic and light indication.
Schematic diagram of the probe is shown in the figure.
An asymmetric multivibrator is assembled on transistors VT1, VT2. An electromagnetic telephone BF2 is installed in the collector circuit of transistor VT1. The device is powered by a 9 V battery, the HL1 LED is connected in series with it. There is no power switch, since in the initial state (pins X1 and X2 are not connected to each other), the supply voltage is not supplied to the multivibrator.
The device works as follows. When connecting the terminals of the probe X1, X2 to each other, the supply voltage is supplied to the multivibrator, it starts to work - an acoustic signal is heard, and the HL1 LED is on. If you connect a relay coil, a transformer winding, a choke or a resistor with a resistance of not more than a few hundred ohms to the terminals X1, X2, then the volume of the acoustic signal and the brightness of the LED decrease slightly. As the resistance increases, the volume of the signal decreases, the brightness of the LED decreases, then the multivibrator stops working and the acoustic signal disappears. A little practical experience will allow "by ear" to evaluate the resistance of a controlled radio element.
The probe can determine the health of the pn junctions of diodes, LEDs, bipolar transistors, the type of conductivity of transistors and the purpose of the diode pins. The element under test, such as a diode, is connected to the probe. In the absence of acoustic and light signals, the polarity of its connection is changed, and with a working diode, a signal should sound and the LED should light, while the anode will be the output that is connected to the X1 "+" contact. If in both cases there is no signal connection, the diode burned out, but if a signal sounds, the pn junction is broken. Similarly, they check the LEDs and evaluate the health of the transitions of bipolar transistors, determine their structure.
When checking oxide capacitors, they are connected to the probe with polarity. At the initial moment, the tested capacitor is charging - the LED flashes and an acoustic signal is heard, its duration depends on the capacitance of the capacitor. When charging is complete, the signal stops. If the volume of the signal decreases, but it continues to sound, the capacitor has a large leakage current.
In the device, you can use a constant resistor C2-23, MLT tuning - SPZ-3 or SPZ-19, transistors of the series - KT315, KT361 with any letter indices. We can replace the AL307BM LED with another one of any glow color, preferably with increased brightness, for example, red glow color - KIPD21M-K, L-53URC; green - KIPD21M-L, L-53MGC; yellow - KIPD21M-Zh, L-53SVT. Telephone BF1 - DEMSh or electromagnetic acoustic emitter HCM1212A, NCM1612A, as well as similar with a coil resistance of 100 ... 300 Ohm. To power the device, galvanic batteries "Krona", "Korund" or a battery of 6F22 batteries are suitable.
All parts, together with the battery, are placed in a case of a suitable size, using surface mounting. The LED is installed in a hole on the housing wall. In addition, a number of holes are made next to the phone for an acoustic signal. The probe leads are made with multi-colored flexible wires (for example, red for X1, blue for X2) with metal probes or crocodile clips.
Adjust the probe with a trimming resistor R2. The conclusions X1, X2 are interconnected, and this resistor achieves stable operation of the multivibrator. If necessary, the frequency of the acoustic signal is set by selecting the capacitor C1.
Author: D.Yurin, Kholmsk, Sakhalin Region
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