First steps in radio, many often begin with independent fabrication of a transistor radio. Along the way, introduces the electronic components, acquired the skills in installation and work with measuring devices. And achieve rapid practical results is to the same positive stimulus for further study of fundamentals of electronics, gives confidence in their abilities and capabilities.SIMPLE RECEIVERS ON TRANSISTORS
First steps in radio, many often begin with independent fabrication of a transistor radio. Along the way, introduces the electronic components, acquired the skills in installation and work with measuring devices. And achieve rapid practical results is to the same positive stimulus for further study of fundamentals of electronics, gives confidence in their abilities and capabilities.
Electronic devices based on microprocessors and integrated circuits are less sensitive to the parameters of the supply voltage. To ensure the safe operation of these devices use voltage regulators with protection. In many power supplies is reduced to cut power to the circuit if a short circuit in it or a sudden increase in load current. Such, for example, the popular voltage stabilizers КР142ЕН5. 
As you know, speaker of the personal computer (PC) it is necessary to include separately. If they are installed at some distance from the operator, this situation is hardly comfortable, especially if the user wishes to view on a DVD movie recorder or any other video, accompanied by sound effects.
Two LEDs with different color (e.g., red and green), you can build a simple indicator for voltages from 4.5 to 220 V. It is also able to determine the polarity of the source in the range 8-220 V. When measuring AC voltage, both diode glow, but if it is constant — lights one of them depending on the wiring polarity indicator. The scheme proposed by the Czechoslovak journal “Amaterske Radio”.
The well-known school electroscope, which demonstrate the phenomena of electrostatics, determines only the presence of electrostatic charge. What is it, positive or negative, we can only guess. This shortage is deprived of the device designed for young hams syut Nadvirna town, Ivano-Frankivsk region. It not only determines the sign of the charge, but also its approximate size.
Our magazine has already told about this exciting game, made on the electromagnetic relay (see “M-K” №1, 1976). And today hams instead of contact devices are widely used in their structures with modern elements as transistors, thyristors, LEDs, integrated circuits. New versions of the game “Who is faster?” with the use of such devices and readers.
Instead of bulky and uncomfortable electrostatic machines Wimshurst, coils Ruhmkorff in high school physics classrooms are increasingly high voltage converters voltage. They can be used to Pro* led experiments in such branches of physics as electrostatics and current in gases. We offer our readers “e-stick” — one of those devices.
As you know, the greater the number of elements in the design, so it is less reliable. To increase the reliability of electronic devices and selection circuitry. This will be the conversation below.
Permissible variation of AC voltage in household electrical network In the 220 — ±5 %. A more significant increase in voltage may result in damage to consumers of electric energy. In the cities, compared to villages, mains is more stable, which is ensured by the presence of numerous compensation substations, powerful transformers which equalize” voltage with changes in energy consumption However, in spite of it. in the evening and night hours, especially in summer (when not in use electric heating devices) due to the natural reduction in electricity consumption (all asleep), the voltage could rise to 245 — 250 V.
Electronic control units of tension are not new in modern developments. The proposed device differs from the majority of them use as the base timer КР1006ВИ1 and unusual sound effect that is activated if the power of controlled DC voltage, thanks to the use of flashing LEDs L36- piezoelectric capsule with a built-in generator emits a sound similar to the siren of the fire truck.