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ABOUT TECHNOLOGY AND ELECTRONICS-DIY
Tehnium Magazine no.1 - 2006 - Panel of static relays controlled by wires
The article, intended especially for beginners, tries to make a modest contribution to better knowledge of magnetic materials.
Known since ancient times, permanent magnetic materials became widely used only after electricity became the focus of attention of physicists and engineers and became widely known.
The first references to magnetic properties
The first reference to the magnetic properties of magnetite dates back to the year 2369 BC from China.
In Europe, the phenomenon is remembered by Tales of Miletus in 585 BC, then described in a book in 1269 by P. de Maricourt, nicknamed Petrus Peregrinus.
At that time, the compass, invented by the Chinese, was already known in Europe. In 1600, in the book "De Magnete" highly praised by Galileo and Kepler and later supported by Newton, the English physician W. Gilbert compares magnetic attraction with electrostatic attraction and tries to explain this property.
John Michell and B. Franklin
In 1750 John Michell explained magnetic induction and a year later B. Franklin shows that electricity can magnetize and demagnetize iron needles.
Andre-Marie Ampere
Then, in 1823, AM Ampere develops a theory that connects electricity and magnetism, paving the way for modern electrical engineering.
The first magnets used at the end of the century XIX when generating electricity, they were made of hardened steel blades, magnetized and placed on top of each other, and had very weak magnetic properties.
At the beginning century XNUMXth 6% tungsten steels appear, then 3.5% chromium steels and cobalt steels, with better and better properties and after 1920 the Alni and Alnico alloys, still widely used today.
After the Second World War ferrites, SmCo magnets and lately NdBFe magnets appear.
Classification and properties:
From the point of view of the behavior in the magnetic field, there is tkinds of materials:
diamagnetic materials (Ag, Au, Cu, Bi, Pb etc.); they do not magnetize and a bar suspended by a wire in the magnetic field tends to sit perpendicular to the lines of force of the field, or to be repelled outward in the case of bismuth;
paramagnetic materials (Cr, Mn, K, AI, Sn etc.); they are weakly magnetized, and the suspended bar is oriented in the direction of the lines of force;
ferromagnetic materials (Fe, Ni, Co); they magnetize strongly even in weak fields and sometimes the magnetic properties remain even after the field disappears.
2. AC rectification
AC voltage rectification assemblies are indispensable in almost all electronic applications powered by the alternating current network.
Despite the apparent simplicity of the recovery schemes, the rigorous analysis of the operation, of the waveforms, especially in the case of loads with reactive components (inductors, capacities), is quite complicated.
Fortunately, however, in most practical applications some mathematical considerations can be ignored that would give an extra precision to the calculations, exploiting only the conclusions strictly necessary for the design.
3. Doubling the audio power
The essential function of an amplifier
The essential function of an audio power amplifier is to take an audio frequency signal of hundreds of millivolts "audio coded" and finally amplify it in power (voltage and current) so that it is possible to transfer electricity to the load impedance, consisting of the group of speakers in the acoustic enclosure.
The transmitted electric power will contain the information of the musical program we want to receive. The conversion of electric power - acoustic power is done with the help of acoustic enclosures with speakers.
The output power of an amplifier
This is defined as the ability of the amplifier to develop a certain electrical power over a long period of time, when it delivers power to the acoustic enclosure.
According to the laws of electrical engineering (which students learn from the XNUMXth grade), the unit of measurement of active power is the watt, and for an electrical circuit the electric power is directly proportional to the electrical voltage present at the load impedance terminals (speakers in acoustic enclosure) and the electric current passing through them…
5. Mechanical stopwatch with electronic alarm
Along with specific utensils, today's kitchen also requires the existence of a laboratory timer, because it itself is a laboratory.
In specialty stores, kitchen timers are almost always mechanical and for this reason their bells work only for a few seconds, because the force of the spring is very low and it must ensure, first of all, the function of measuring time.
For this purpose, the addition of an electronic alarm, triggered by the mechanical bell hammer, proves its usefulness.
The assembly consists of a thyristor that triggers the electronic alarm when the contact is closed (K1), actuated by the hammer of the mechanical timer.
6. Rectifier stabilized with LM317
To operate consumers with different powers, higher or lower, supplied with direct current at various voltages, it is practical to have a rectifier with variable voltage, stabilized, which can be viewed through a Moorish instrument attached to the source.
Such a very simple - but very efficient - electronic scheme for the continuous regulation of the electric voltage in the range 1.3 - 24V and high amperage (intensity) (established by the amateur manufacturer) is presented in the article.
7. Device for checking remote controls
In TV troubleshooting, various verification and control devices are often needed. The exception is not the operation of checking the remote controls. A simple and efficient assembly for this purpose is presented in the article. The scheme is based on an infrared radiation sensor produced by the company Vishay Telefunken.
8. MMC 22925/6/7/8
These integrated circuits contain 4 counters with storage circuits (Latch). The 4 counters are internally multiplexed and are decoded by a BCD-7 segment circuit to operate common cathode displays.
The maximum current for a segment is 40mA. For external multiplexing, 4 Aout, Bout, Cout, Dout outputs are available, with a maximum output current of 1 mA.
The multiplexing is controlled by an internal oscillator (without external components) with an output frequency of approximately 1 kHz. The maximum working frequency of the counters is 4MHz, with switching on the negative front of the clock signal.
A level "1" on the RESET input brings all counters to zero, including the CARRY OUT output in the logical "O". A logical "O" on the LATCH ENABLE input determines the storage of the contents of the counters in the storage circuits. Level "1" on the DISPLAY SELECT input selects the digit from the counter for display, and for level "O" selects the digit stored in the storage circuits.
9. Digital frequency meter
The article presents the construction of a digital frequency meter, which presents a series of features that make it accessible to most amateur builders, namely:
use of specialized CMOS circuits;
use of a simple and efficient time base;
The characteristics of the obtained frequency meter are:
measuring range: 50Hz - 1 MHz;
minimum input voltage: 100mV;
supply voltage: 5V;
maximum absorbed current: 100mA.
10. Automatic hand dryer
The proposed assembly uses as a detector an optocoupler by reflection, whose emitting diode is controlled in short current pulses, but with a much higher value than the nominal one.
The pulse generator is a relaxation oscillator made with a type comparator LM339, according to a classic scheme.
11. Wired-controlled static relay panel
The main advantages of static contactors over electromagnetic ones are: lack of moving mechanical parts, very short switching times, small size, low control power, high reliability.
The proposed assembly can control two optotriace MOC 3063 or MOC 3083 by two lines with two wires each.
It was decided to place the optotrias as close as possible to the ordered elements because they usually work with high voltages and currents.
