The analog to digital conversion is based on theoretical sampling theorem and the concepts of quantization and coding.

A first classification of the A / D, is the following :

• Conversion direct transformation.
• Converters with conversion (D / A) intermediate auxiliary.

Capture and holding circuits (S / H: Sample and Hold).

The Capture and holding circuits are used for sampling the analog signal (during a time interval) and then holding this value, usually in a capacitor during the duration of the conversion A / D itself.

The basic layout of a  Sample and hold circuit, and its simplified representation, is given in the figure above

The operation of the circuit of the figure is as follows: The A / D converter sends a pulse width tw by line C / M, which activates the electronic switch, charging the capacitor C, during the time tw. In the ideal case, the capacitor voltage follows the input voltage. Then the capacitor keeps the voltage acquired when the switch opens.

Response of a sampling and hold circuit

The graph has an ideal character, since both the charging and discharging of the capacitor are closely related to its value and that of the resistances and parasitic capacitances associated with the circuit.

Emphasizes the fact that the control signal C / M is from the A / D converter, which is the only one to know the time that the conversion is complete signal.

A / D converter with comparator

It is the only case in which the processes of quantization and coding are clearly separated. The first step is performed by comparators that discriminate between a finite number of voltage levels. These comparators receive at its inputs the analog input signal with a reference voltage, different for each. Being staggered reference voltages, it is possible to know whether the input signal is above or below each of them, which allow to know the state that corresponds as a result of quantification. Then will need an encoder that give us the output.

Basic diagram of a converter with comparators.

This converter is a high speed, since the direct conversion process is rather than sequentially, thereby reducing the time necessary conversion to the sum of the propagation times in the comparator and the encoder. However, its usefulness is limited in cases of low resolution, since for an N-bit output are necessary 2N-1 comparators, which leads to excessive complexity and higher cost is desired as a high resolution.

Using the simple circuit of A / D and basically consists of the elements shown in the following figure :

Basic diagram of a converter with counters

A comparator, clock, circuit capture and holding (S & H) counter D / A converter and output buffers.

Once the trapping and holding circuit (S / H) is sampled analog signal, the counter starts running counting the pulses from the clock. The result of this count is converted into an analog signal by a D / A converter, proportional to the number of clock pulses received up to that moment.

The analogue signal obtained is introduced to the comparator in which a comparison is made between the input signal and the digital signal converted to analog. At the moment when the latter reaches the same value (actually slightly larger) than the input signal, the comparator output toggles its stoppage occurs and the counter.

The counter value becomes the buffers and becomes the digital output corresponding to the input signal.

This converter has two drawbacks:

• Low speed.
• Conversion time variable.

The second drawback can be easily understood with the help of the following figure, which shows that the number of clock pulses (time), needed to achieve the value Vien the D / A converter depends on the value of Vi.

Said conversion period is given by the expression :

A diode for reverse polarity protection
Of course, there is a polarized connector system such as the hollow plug. For many small self-built circuits, voltage circuits for testing, often taken from the power supply. And because it can happen that you accidentally turn on the power supply with the wrong polarity on the circuit, which makes your project vain. Even when soldering hollow connectors can happen the same.

For circuits with such errors can not be avoided, but is there any simple protection? yes, with the installation of the polarity protection diode in the positive supply voltage of the circuit!

Diodes mounted so that the anode is connected to the positive terminal ofvoltage source and the cathode to the positive terminal of the circuit. If thecircuit is connected to the correct polarity, the current flows from thepositive terminal through the diode in the circuit and the negative terminalback to a voltage source.

If the circuit is accidentally connected to wrong polarity (the positive voltage to the negative terminal of the circuit), no current can flow because it flows in the ”wrong” direction (this will be blocked by diode).

When installing a protection diode we must consider two things :

• Diode should be able to cope current consumption of the circuit.
• In the diode voltage drop of about 0.7 volts, ie, the circuit gets about 0.7volts less than the applied voltage.

Fluorescent lamps Design and function
Fluorescent lamps are one of the gas discharge lamp. It consists of a glass tube, which with mercury vapor and an inert gas such as argon or krypton filled. The inside of the glass tube coated with phosphor. This converts the light generated in the operation of the ultraviolet light in a longer wavelength, ie, into visible light.

The lamp has two electrodes made of tungsten. By a short voltage pulse, the gas is ionized and therefore electrically conductive. To generate this ignition voltage, a ballast is required. Conventional control gear (CCG) consist of a choke coil and a starter. The starter consists of a neon lamp and bimetal. Parallel to the starter, a capacitor is connected to the radio interference suppression.

The ballast is connected in series with the fluorescent lamp. Parallel to the lamp is the starter. When switching a small current from the ballast flows through the first electrode of the lamp by the starter to the second electrode of the lamp and from there to the N-conductor. It comes to glow in the neon lamp to the starter. This heats the bimetal and which close to the neon lamp is shorted and goes out. Now, a high current from the ballast flows through the electrode of the lamp by the starter to the N-conductor. Due to the high current builds in the choke coil of the ballast to a magnetic field. Simultaneously by the high power of the lamp electrodes are heated. Electrons out from it.

Since the shorted glow lamp is not lit in the starter to cool the bimetal again – they open up again and the circuit is interrupted. This interruption of current flow causes a collapse of the magnetic field in the ballast. The collapsing magnetic field generated by the self-inductance of the choke coil a voltage surge of nearly 1000 volts. This high voltage is applied to the electrodes of the lamp and accelerates the electrons in the lamp at high speeds – the gas electrically conductive and light the lamp.

This usually runs from ignition process several times until it comes to a stable ignition. Therefore, fluorescent lamps flicker when turning several times until they light up. Since the ballast is an inductive resistor in the ground, this also has a power consumption which is around 10 watts. We must therefore not only the power of the fluorescent lamp to see solely, but must also add to the ballast! Nevertheless, the power consumption is significantly lower than the same light bulb!

A disadvantage of an individually-operated fluorescent lamp, is that it flickers to the rhythm of the line frequency of 50 Hz. Therefore, fluorescent lamps lamps are often offered as a double with two tubes in so-called double switch. This, the second lamp has a capacitive ballast. This leads to a phase shift of 180 degrees between two lamps, which cancels the flicker.

Today, apart from the conventional control gear(CCG), there are also electronic control gear (ECG). It is much more expensive, but it has several advantages:

• Soft in the lighting
• Low power dissipation
• With high-frequency operation, no blinking lights
• There is no reactive power compensation required

Finally, note:

Never broke a fluorescent light! Glass tube containing a small amount of mercury which toxic! Therefore, this lamp in any case should not disposed in the trash, but should be brought to the collection!

Battery care tips

Never buy batteries for stock!
During long storage battery has a certain self-discharge, and this will increase at higher temperatures. Batteries are depleted (also alkali-manganese batteries!) May leaks, it is partly demonstrated by the fact that it has been stored in the contact of a white powder (potassium hydroxide). It is corrosive and corrodes all the metal parts that come into contact with it.

Do not use different batteries in one device!
For any reason, do not mix new cells and cells used. Every chain is only as strong as its weakest link. One cell is weak, will lower the total system voltage, although other cells are new.

Always check the correct polarity!
Battery providing a DC voltage, which always has a polarity. It is always important. Reverse polarity often lead to damage.

Do not ever try to recharge the battery!
Primary cells are not rechargeable and destroyed in the attempt.

Avoid short circuit!
With the continuous short-circuit the battery may become hot. There is also a risk of exploding and things are not funny. Therefore, the battery should be stored in such a way as to avoid short circuits.

Do not ever try to open the battery!
Batteries contain hazardous materials and corrosive.

Remove the batteries in device when not in use!
Leaking batteries corroded contacts can damage the device. Corroded battery contacts can not be repaired.

Expired batteries should be removed immediately!
Residues of the expired batteries of the the device should be removed as much as possible and thoroughly cleaned repository.

Do not throw batteries in the trash!
They contain harmful substances and environmental pollutants, Today batteries can also be disposed to the dealer.

To calculate the buffer the capacitor, we will change the above formula becomes:

Uhum = 10 ( I / C )

Uhum : Voltage hum (Vp)

I : Current (mA)

C : capacity (uF)
(in single-phase rectifier, a factor of 10 replaced with 20) Note that the peak voltage at buffer elco is 1.4 higher than the voltage transformer.

C =  10uF. ( I / Uhum )

Example : A supply voltage of 18 V consists of transformer, rectifier bridge, and a buffer elco. How much capacity should be, so that the output voltage is not dropped below 20 V, with 520mA maximum current?

We need to know first, what is the maximum peak of voltage hum. It consists of half period peak voltage and minimum voltage (Image above). So the highest voltage is :

18 V x 1.4 V = 25.2 V

Voltage hum:

25.5 V-20 V = 5.2 V

According to the above formula applies:

C = 10uF (520 / 5.2) = 1000uF

• power loss
• value and SWR
• etc.

Power loss:
If you are have an RF power amplifier that delivers 5 Watt for example, we must ensure that the 50Ohm dummy load can resist that power. To do this we place the resistors in parallel this way:
The parallel resistance N (in our example 4) increases the power handling of the load by a factor of N but also divides the value of resistance by N.

If each 200ohm resistor can dissipate ¼ Watt, the four resistors in parallel will dissipate 1 watt.
The value of the load will be 200 / 4 = 50Ohm (what we want).

For a power of 10 Watt for example we can use 1 watt resistors 10 or 40 ¼ Watt.

However it will ensure that the size of the load is not too important to avoid the introduction of parasitic elements: capacitor formed by two plates supporting the resistance of epoxy for example.

Adjusting of the load:

If you can not find in the standard values ​​of resistance, the value needed to get a load of 50Ohm, it is always possible to be 51 ohms for example and reduce this value by using different value of resistance .

51 Ohm in parallel with 3300Ohm (3.3kOhm) will form an equivalent resistance of 50.22Ohm.

The SWR thus obtained will be very low and very close to 1: 1.0044

Note for the building:

• Use non-wirewound resistors (carbon layers classic will do) in order not to introduce reactive component (inductive in this case) and final distort the impedance of the load.
• Make connections between resistors short: each end of tracks behave (depending on the frequency) as an inductor.
• Good heat dissipation by the load. 5Watt is a tremendous power for a ¼ watt resistor and it is likely to behave badly or break, which may damage your transmitter.

Attention, “all that is observed is changed.” Asking the probe alters the signal. HF caution should be used primarily for sensitive mounting (oscillators, hyper editing etc.)..

Older models have a tube. The electron beam is deflected by a plate with your polarized signal. These are known analog oscilloscopes.

The units now have all-digital LCD digital color also known as digital oscilloscope. It also have a memory that saves your curves and capture a lot of data. The operating principle is as follows:

• The signal is amplified
• It is then filtered by a filter antialising, which prevents the recovery of spectrum in the sample.
• It is then sampled using an analog-digital : data is digital and can then be treated with a DSP.

The advantage of digital oscilloscopes is undeniable : the curves can be stored, treated subsequently, sent to a PC with editing software, included in a report, etc.. In addition, memories are more important, allowing large, detailed zooms despite high time bases.

Recently we saw the emergence of digital oscilloscopes with a display simulating that of an analog oscilloscope : the resolution of the screens are using technology more and more important.

What kind of heatsink you choose?
In electronics, most heatsink you will find are black anodized aluminum. Some are pre-drilled, others are rough casting. Course it is more convenient to choose a model that can serve as pre-drilled soon acquired, if the component to be cooled is provided with one or more holes. Undrilled models are preferred when it comes to cutting the heatsink to a size that does not exist in any given market. The different models are available all have a common characteristic that should not scare you, and that is the thermal resistance, Rth denoted. Remember, this thermal resistance is expressed in ° C / W and represents the temperature rise per watt dissipated. Over the heatsink is small, and its thermal resistance is high (at least it will cooling).

Below are some examples of heat sinks :

Heatsink TO 5 case (transistor 2N2219 for example), model ML61, Rth = 55 ° C / W

Heatsink TO 5 case (transistor 2N2219 for example), model CO180, Rth = 28 ° C / W. In view of the thermal resistance of the heatsink, we see immediately that the cooling will be better than the ML61, presented just before.

Heatsink for  TO 220 case (or triac type TIC226 type LM7805 voltage regulator, for example), model ML24, Rth = 17 ° C / W. Model fairly typical and widely used.

Heatsink for TO 3 case (2N3055 for example), simple model ML25, Rth = 2.4 ° C / W

Heatsink for two TO 3 case (2N3055 for example), double model ML25, Rth = 2.4 ° C / W

The value of the thermal resistance of (large) heatsinks fins is sometimes specified for vertical mounting, the value may be different when the heatsink is mounted horizontally (slightly higher).

Some manufacturers specify two values ​​for thermal resistance components: value no heatsink and value with heatsink. Sometimes two values ​​are specified for the presence of heatsink with thermal grease, and grease. Be curious and look at the difference between these values ​​…

Copper Heatsink?
There are also actually copper heatsinks, aluminum or half copper half. Have a look at the heatsinks for PCs sold by the manufacturer Zalman, for cooling the processors on motherboard (CPU) and graphics processors (GPU). Copper has a characteristic heat transfer somewhat better than aluminum, but also a little more expensive. One might think that the choice of copper is the best direction to take, but the game does not always worth the effort. In any case, nothing prevents to consult specialized forums to see what it says.

Calculation of the Heat sink

• The junction between the component and its case. Its value is specified in data sheets of manufacturers.
• The one between the housing component and the heat sink. It depends on the housing component, and is generally between a few tenths of ° C / W and a few tens of ° C / W. This value is also specified in the manufacturers’ data sheets (but unfortunately not always).
• between the heat sink and the ambient air. This value is given by the manufacturer of the heat sink, and is even lower than the heat sink large.

For a total thermal resistance (junction between the component and ambient air), simply add the three thermal resistances above. It would be unwise to be satisfied with this simple addition, without considering some small safety margins. We must indeed avoid the component work continuously too close to the limit, and consider some cases of “overheating” natural (equipment exposed to the sun) or less controllable (failure of a fan). Remember that when it comes to room temperature, refers to the air surrounding the component or the radiator, and if it is enclosed in a box, its temperature will not be the one you think.

Example heat sink calculation 1
We want to cooling a 2N3055 type transistor in which case TO3 must dissipate a power of 20 W at room temperature. First recall the simplified formula announced at the beginning of the article:

Rth = (T1 – T2) / P

Now replace T1 by Tj (junction temperature), T2 Ta (ambient temperature) and P with Pd (power dissipation). this gives

Rth = (Tj – Ta) / Pd

First thing, take a safety margin. We will base the calculation on a 25% higher power dissipation, or 25 W instead of 20 W. Room temperature is estimated at 55 ° C (it sounds a lot, but it happens more often than one thinks), the component and heat sink are enclosed in a box. The manufacturer indicates for the 2N3055, resistance junction-case of 1.5 ° C / W, and a resistance heater box-0.5 ° C / W with silicone grease. According to the manufacturer, the maximum temperature junction is 200 ° C. By applying the above formula, we get this:

Rth = (200-55) / 25 = 5.8 ° C / W

Thermal resistance of 5.8 ° C / W which should be deducted resistance junction-case of 1.5 ° C / W resistance heater box-0.5 ° C / W. Finally, we find that we need a radiator thermal resistance of 3.8 ° C / W. A radiator of thermal resistance but also lower should take more space for you to find a mechanical model that suits the application.

Basic for heat sink calculation

Heat sink Calculation method
To begin, we agree that the thermal resistance, which we call now Rth, can be represented in the same way that the electrical resistance used in electronic assemblies. This allows you to navigate easily, even with a diagram of usual type:

The heat dissipated by the component gaining the environment via several ways:

• the junction box of the component to the component, radiation and conduction;
• the housing component to the surrounding air by radiation and convection;
• the housing component of the radiator by conduction;
• the radiator to the surrounding air by radiation and convection.

The junction of the inner component is the component whose temperature must not exceed a certain limit the risk of being destroyed. The limit value is specified by the manufacturer of the component, it is about 90 ° C for germanium and components from 150 to 200 ° C for silicon components. Note that the calculation methods used for electrical resistors are applied to the thermal resistance, with respect to the in series or in parallel.

Thermal equilibrium of the component
To talk about things, take the example of a transistor. The latter receives a power that depends on the voltage applied between its collector and emitter, and the current through the collector. Refer to this power received PC (power consumption). Because of this received power Pc, the transistor will dissipate some energy, which we call Pd (power dissipation). The transistor tends to thermal equilibrium when the power dissipated equals the power consumed, ie when Pd = Pc. If now we call the junction temperature Tj and Ta the ambient temperature, we can write the power dissipation Pd is equal to (Tj – Ta) / Rth. You can also write this:
                                              Tj = Pd * Rth = Ta
We realize and recognize that the junction temperature of the transistor depends at the same time the total thermal resistance, ambient temperature, and of course the power dissipated in the transistor. Based on this observation, we realize that it is possible to calculate the cooling system according to the power terminal and the maximum allowable power dissipation. Next : Calculation of the Heat sink , Example heat sink calculation .