Tehnium Magazine no. 4 - 2005

Tehnium Magazine no. 4 - 2005 - Automatic for water tanks

Reading time: 4 minute

The main topics discussed

1. What would be useful to know about regression diodes to optimize assembly performance?

Rectifier diodes with germanium (Ge) or silicon (Si)

These are very common in electronic assemblies, but sometimes the optimal choice of the type of diode to be used is made in incomplete knowledge of the phenomena and parameters that govern the operation of these common circuit elements. This can affect the efficiency and reliability of the assemblies.

What is a diode?

In essence, a diode is a switching element, which in one sense, called direct conduction, has a very low resistance, and in reverse, a very high resistance.

How does a diode work?

In direct conduction, for relatively low bias voltages, the diode opens and the current increases quite rapidly with the applied voltage.

In reverse, however, the current is very small and is maintained almost constantly for a large range of reverse polarization voltage, and over a certain value of it, called breakdown voltage, the current experiences a very pronounced increase.

The reverse current of the diode has two components. The first component is the saturation current, due to the load carriers in the junction area.

This current is very small, even negligible in silicon diodes. The second component is due to the multiplication of the load carriers under the effect of the applied voltage and is higher than the saturation current.

Reverse voltage at diodes

However, increasing the reverse voltage, we reach the breakthrough area, UBR, where the current increases considerably due to two phenomena: the avalanche multiplication of the load carriers under the action of the electric field and Zener effect, which consists essentially in the release of valence electrons from the crystal lattice.

In the case of ordinary rectifier diodes, if the reverse voltage reaches the breakthrough value and the assembly does not have appropriate elements to limit the reverse current, avalanche breakdown can cause irreversible changes in the junction structure.

Thus, diodes that are able to withstand tens of watts in the direct direction, can be destroyed by watt fractions in the opposite direction, because in the direct direction the heat is released throughout the crystal mass, while in the opposite direction the heat production is local, in points isolated.

2. Automatic for water tanks

Ensuring a water supply for household use is usually done by mounting tanks at a certain height and filling them, with the help of pumps, from the water source: fountain, lakes or rivers, etc.

Another solution is to use hydrophones, but this solution is expensive, generally valid for low water consumption.

The article presents the electrical diagram of an assembly that allows the automatic control of the operation of the water pump so that the level in the tank is maintained between two limits, minimum and maximum; this is if we opted for the first option of water insurance.

3. Filters for speakers

Under this name are recognized by most assemblies that separate the working range of speakers mounted in the same acoustic enclosure.

More correctly, these are called passive speaker separation networks, taking into account that there are also active (electronic) separation networks, which are introduced in the acoustic chain before the power amplifier.

This approach will only include clarifications and practical advice in addressing this issue, based on the author's experience and the many materials studied and used over time, without resorting again to mathematical formulas and computational relations, especially as in time, they were published several times in the pages of the magazine.

4. Stereo digital potentiometer

Digital controls are very common lately and have replaced, in many cases, analog controls.

The presented assembly can be used by those who have medium and high power amplifiers; it replaces analog stereo potentiometers.

The low number of components, the low voltage supply and the very good response time make this very useful digital potentiometer.

5. Construction of plastic boxes

Devices powered directly from the 220 V mains (without transformer) presents a danger of electric shock and must be mounted only in plastic boxes.

In trade there are PVC or ABS boards with a thickness of 2… 3 mm, of various colors, which is a very suitable material for construction, as well as specific adhesives for each material. PE or PP boards cannot be used because neither polyethylene nor polypropylene can be glued but only welded, the process is not within the reach of the amateur, most of the time the appearance is not appropriate and the materials are mechanically processed very poorly.

Apparently the simplest way of construction would be to cut all the components and then glue them, but this way of working does not lead to good results either in terms of rigidity or appearance, and in fact it is much more complicated to achieve, so a construction made by bending and with a minimum of welds gives much better results. For this it is necessary to build a hot wire bending device.

6. Modified FD4 antenna

The FD4 antenna, used by many radio amateurs, is an asymmetrically powered dipole with uneven arms. 13.8 m and 27.7 m, respectively.

Since the input impedance is approx. 300 ohms, the antenna is supplied by adaptation / symmetry transformers having transformation ratios of 1: 4 or 1: 6, depending on the characteristic impedance of the coaxial cable used: 75, respectively, 50 ohms.

The antenna works satisfactorily in the classic shortwave bands, ie at the frequencies of 3.5; 7; 14; 21 and 28 MHz.

By introducing two additional arms of 4.7 m and 9.4 m respectively, the FD4 antenna will be able to work even in WARC bands.

The term "WARC Tapes" refers to the bands of 30, 17 and 12 m, ie to the frequency ranges between: 10.100 - 10.150 kHz, 18.068 - 18.168 kHz and, respectively, 24.890 - 24.990 kHz. These are often called WARC bands because they became available to radio amateurs later World Administrative Radio Conference since 1979.

However, in Romania the access of radio amateurs to these bands was not immediate, but it was done starting with 1982.

7. Webra FMSI remote control station

Webra remote control station, of Austrian manufacture, is a high technical equipment. Works in 27 bands; 32; 35 or 40 MHz, as the case may be, SMS system and frequency modulation.

The station can control up to 7 servers. Because the dimensions and weight of the execution reception assembly are small, it can be used very well in directing both ship models and air models with electric or thermal propulsion.




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