The main topics discussed
1. Differential supply of operational amplifiers
Assemblies made with operational amplifiers (AO) or with integrated voltage comparators can be supplied either from single DC voltage sources, U, or from differential voltage sources, + U and -U in relation to a common zero point.
The option between the two solutions belongs to the developer of the application in question, but there are also situations in which the differential supply is imposed by the nature of the scheme (for example, in order to be able to perform the offset adjustment).
The authors of the articles that present various assemblies with AO sometimes specify the possibility of supply either with single voltage or with differential voltages, but I don't always remember the concrete way in which the scheme is transposed from one type of supply to another.
Of course, these things are supposed to be known, but there are always beginners who have not yet met them. At the beginning, amateur builders limit themselves to making various montages, selected from books or magazines just as they are presented there.
Then, gaining theoretical and practical experience - often meeting some needs, lack of equipment, etc. - they gain courage and begin to "walk" through the schemes of principle, often with good results, which give them an incomparably greater satisfaction than the "mechanical" copying of the solution proposed by the author.
2. Adapter for sorting Zener diodes
The assembly described in the article was thought of as a adapter to a pocket multimeter with digital displayl, M, put on the range of 20V direct voltage, the power supply being made from a 9V tp 6F22 battery.
It has been designed to the maximum possible simplicity, being intended for the rapid venification / sorting "on the field" of the Zener diodes of low voltages (below 7.5V).
3. Hafler DM200 amplifier
After the widespread appearance of side power MOS-FET transistors complementary (2SK134, 2SK135, 2SJ49, 2SJ50), launched by HITACHI in 1977, the American company HAFLER launched the DH 200 amplifier, whose performance can be considered today at the top level.
The main features are:
Rated power: 100 W / 8 Ohm;
Harmonic distortions: 0.02% in the band 20 Hz - 20kHz;
Intermodulation distortions: <0.005%;
Frequency band: 10Hz - 40kHz +/- 0.5dB at 100 W / 8 Ohm
Input impedance: 22 kOhm;
Sensitivity: 1.5 V RMS for 100 W / 8 Ohm;
Response speed: 30 V / us
Power consumption: in empty 100VA, in load 470 VA.
4. High-performance audio amplifier (30W)
This audio amplifier was practically made by the students from the XNUMXth grade, of industrial electronics profile, constituting at the same time an excellent subject regarding a practical application for Professional Skills Exam.
Initially estimated performance (and, in fact, practically confirmed) of the audio amplifier are the following:
Rated power: PN = 30W;
Input impedance: Day = 47 kOhm;
Output impedance (load): Ze = 8 Ohm;
Input voltage Ui: = O.85 VRMS;
BW frequency band: 15Hz - 35kHz;
Attenuation at BW ends: ABW = -3dB;
S / N signal / noise ratio: = 75dB;
Growth rate, slew-rate: SR> / = 20 V / us;
Total harmonic distortions: THD
Intermodulation distortions: TID
Supply voltage: UA = +/- 30V;
Idle current: Io = 70mA;
Rated current: IN = lA;
5. Insect removal
Problems with insects and especially mosquitoes are daily, especially in summer.
Most insect repellent schemes use audio generators on various frequencies, starting with 15 kHz and ending with 40 kHz, some with asymmetrical waveforms, to have plenty of harmonics.
Almost all of these assemblies have proven ineffective in fighting insects.
The article presents a montage that attracts various insects, especially in the evening, and removes them. This circuit works with dangerous voltages and must be handled with the utmost care during testing and commissioning.
The assembly consists of a lamp (fluorescent tube or bulb) which is surrounded by a metal network connected to high voltage and low current.
6. Electronic igniter
The proposed scheme is an electronic stove igniter that operates at low voltage, + 3V. The assembly is made according to the scheme of a Chinese-made device, which is commercially available.
At the base, it is a self-locking voltage converter, made with the transistor T1 (pnp) type BD 238 (in the original scheme is used S8550 / 40V / l.5A / 1W / l00MHz) and a transformer made on the ferrite pot with the primary winding (from the collector) of 95 turns, the reaction (from the base) of 75 turns, and the secondary 800 turn voltage booster.
The secondary voltage is rectified with the diode D1 BA159 (FR107) and is applied to a circuit for producing the high voltage required for the electric arc.
The circuit consists of a thyristor and a minitransformer made on a ferrite rod with a diameter of 4 mm and a length of 30 mm, on which are wound two windings: the primary, 32 turns, and the second, 1900 turns divided into 7 sections along the entire length of the ferrite, placed for the first winding.
According to statistics, a European spends 8 hours at work, 7 hours in the living room and 7 hours in the bedroom. We spend most of our day indoors (according to the statistics above, 90% of our time).
Thus, the quality of the air we breathe and the factors that influence the air quality inside the rooms are not indifferent at all.
What is air made of?
As we know, air is composed of 78% nitrogen, 21% oxygen, and the remaining 1% composed of various gases. Although we need "oxygen-rich" air, the oxygen concentration in the air can drop to 16% without noticing, and the initial amount of carbon dioxide, which is well below 1%, can increase by three. four times, without causing any problems.
How is ozone formed?
In offices, ozone is formed by the electrical voltage that is required for photocopying, a process in which oxygen molecules composed of two atoms disintegrate into oxygen atoms.
These free oxygen atoms come in contact with oxygen molecules (O2) and form ozone (O3).
Repeated studies have shown that under the action of natural phenomena such as cosmic rays, solar radiation, electric discharges from the atmosphere, storms, etc., As the oxygen molecule is sensitive, a large amount of oxygen will be found in the form of ions.
When the atmosphere is overloaded with negative ions, it becomes basic, causing the pH to rise and invigorating, increasing work capacity.
Thus, air with its normal concentration Moderately overloaded with negative ions destroys microbes, contributing to good blood circulation.
The artificial field and the beneficial effect of plants are used to artificially restore the ion balance or to create positive or negative superionizations.
An aeroionizing device can be made (like the one presented in the article) to collect from the atmosphere the surplus of ions (negative or positive), this working with voltages between Analog output signals for the voltage range of 2000V - 6000V..
8. Old news: Nuvistoarele
The newcomers are characterized by small dimensions, high mechanical robustness, high operating frequency, low noise and high amplification coefficient. These are just some of the characteristics that have imposed them, at one time, having a widespread use and superior qualities to other electronic tubes.