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| − | <div lang="en" dir="ltr" class="mw-content-ltr">
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| − | The Standard EIA Color Code Table per EIA-RS-279 is as follows:
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| − | {| border="1" cellspacing="0" cellpadding="3" | |
| − | !Color!!1st band!!2nd band!!3rd band (Multiplier)!!4th band (Tolerance)!!Temp. Coefficient
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| − | |- bgcolor = "#000000"
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| − | |<font color = "#FFFFFF">[[Black]]</font>||<font color = "#FFFFFF">0</font>||<font color = "#FFFFFF">0</font>||<font color = "#FFFFFF">×10<sup>0</sup></font>|| ||
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| − | |- bgcolor = "#B8860B"
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| − | |[[Brown]] ||1||1||×10<sup>1</sup>||±1% (F) ||100 ppm
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| − | |- bgcolor = "#FF0000"
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| − | |[[Red]] ||2||2||×10<sup>2</sup>||±2% (G) ||50 ppm
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| − | |- bgcolor = "#FFA500"
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| − | |[[Orange (colour)|Orange]]||3||3||×10<sup>3</sup>|| ||15 ppm
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| − | |- bgcolor = "#FFFF00"
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| − | |[[Yellow]]||4||4||×10<sup>4</sup>|| ||25 ppm
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| − | |- bgcolor = "#9ACD32"
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| − | |[[Green]] ||5||5||×10<sup>5</sup>||±0.5% (D) ||
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| − | |- bgcolor = "#6495ED"
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| − | |[[Blue]] ||6||6||×10<sup>6</sup>||±0.25% (C)||
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| − | |- bgcolor = "#EE82EE"
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| − | |[[Violet (color)|Violet]]||7||7||×10<sup>7</sup>||±0.1% (B) ||
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| − | |- bgcolor = "#A0A0A0"
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| − | |[[Gray (color)|Gray]] ||8||8||×10<sup>8</sup>||±0.05% (A)||
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| − | |- bgcolor = "#FFFFFF"
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| − | |[[White]] ||9||9||×10<sup>9</sup>|| ||
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| − | |- bgcolor = "#FFD700"
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| − | |[[Gold (color)|Gold]] || || ||×0.1 ||±5% (J) ||
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| − | |- bgcolor = "#C0C0C0"
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| − | |[[Silver (color)|Silver]]|| || ||×0.01 ||±10% (K) ||
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| − | |-
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| − | |None || || || ||±20% (M) ||
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| − | |}
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| − | </div>
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| | <!-- 3. Demostrar las técnicas adecuadas de soldadura. --> | | <!-- 3. Demostrar las técnicas adecuadas de soldadura. --> |
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| | <!-- 4. Explicar el uso y funcionamiento de los diversos componentes importantes en la electrónica tales como: --> | | <!-- 4. Explicar el uso y funcionamiento de los diversos componentes importantes en la electrónica tales como: --> |
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| | <!-- 5. Conocer y comprender la ley de Ohm. --> | | <!-- 5. Conocer y comprender la ley de Ohm. --> |
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| − | <math> V = I R </math>
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| − | Where v is voltage (measured in volts), i is current (measured in amps), and r is resistance (measured in ohms). The equation can also be written as
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| − | </div>
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| − | <math> I = \frac{V}{R} </math>
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| − | and
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| − | <math> R = \frac{V}{I}</math>
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| − | </div>
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| − | Basically, it means that if the voltage is held constant and the resistance is decreased, the current is increased. Or if the resistance is held constant and the current is increased, the voltage will also increase.
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| − | </div>
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| − | === Capacitors ===
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| − | Only polarized capacitors are "pinned," and care must be taken to not plug them in backwards. If an electrolytic capacitor is charged in reverse, it can explode. Polarized capacitors are often marked with a stripe showing which terminal is the cathode (negative terminal). Sometimes the stripe will connect the cathode and the anode, but it will have arrows or minus signs on the stripe indicating direction of current flow (anode to cathode). In a schematic, the curved plate of the capacitor represents the cathode and the straight plate represents the anode.
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| − | </div>
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| − | [[Image:Polarized_capacitors.jpg|Polarized Capacitors]]
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| − | </div>
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| − | In the picture above, the cathode of the black capacitor is on the right. The cathode of the blue capacitor is toward the bottom.
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| − | </div>
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| | <!-- 7. ¿Qué se entiende por un circuito en paralelo y uno en serie? --> | | <!-- 7. ¿Qué se entiende por un circuito en paralelo y uno en serie? --> |
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| − | [[Image:Series_parallel_resistors.png|Series and Parallel Circuits]]
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| − | </div>
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| − | In a series circuit the current flowing through both devices will be equal, but the voltage across them will be different if the resistances are different.
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| − | </div>
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| − | In a parallel circuit, the voltage across the two elements will be identical, but the current divides between them. Some current goes through the top, the rest goes through the bottom.
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| − | </div>
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| − | In this circuit, R2 is a cadmium sulfide cell (CdS cell) - that is, a light-sensitive resistor. When exposed to light, the resistance of the cell decreases. In darkness, the cell has a higher resistance. R1 and R2 together form a voltage divider circuit. As the light striking CdS cell gets brighter, the voltage at the common terminal decreases. As it gets darker, the voltage increases. This voltage is applied to the positive terminal of a comparator IC. The negative terminal of the comparator is connected to the wiper of a potentiometer which forms a second voltage divider circuit. This voltage can be adjusted by tuning the potentiometer. When the light striking the CdS cell gets bright enough, it causes the voltage on the positive terminal to fall below the voltage on the negative terminal. This causes the output of the comparator to go to zero volts, thus lighting the LED. When it gets dark again, the LED will turn off.
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| − | </div>
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| − | The action of the LED can be reversed (on when dark, off when bright) by reversing the positions of R1 and R2 (the CdS cell), by swapping the positive and negative terminals of the comparator, or by connecting the LED through a resistor to ground instead of connecting it through a resistor to power.
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| − | </div>
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| − | The frequency of the low-frequency oscillator is set by the capacitor C1, and the resistors R1, R2, and R3. When the output of the amplifier (at pin 1) is high, C1 charges through R1. When the voltage across C1 exceeds the threshold voltage on the positive terminal of the op-amp, the output will go low. When this happens, C1 will then discharge though R1 and the voltage at the positive terminal will change to a negative value. When C1's voltage drops below the threshold voltage at the positive terminal, the output switches high again, and the cycle repeats. The threshold voltage at the positive terminal is set by the ratio of R1 and R2, as well as by the output of the amplifier:
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| − | </div>
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| − | <math>V_{thresh} = \frac{R1}{R1+R2} \times V_{out}</math>
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| − | </div>
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| − | If the voltage at the output of the low-frequency oscillator is observed on an oscilloscope, it will be shown as a square wave, oscillating between the two battery supply voltages. If this value were used to drive the base of Q1, the transistor would switch suddenly between full-on and full-off, and this would cause the audio oscillator's frequency to jump suddenly between two values (this makes it sound more like a cell phone ringing than a siren - try it!). To get a siren-effect, we need a smooth frequency transition, so the base of the transistor is driven with the voltage on the capacitor C1 which is a triangle wave.
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| − | </div>
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| − | The next portion of the circuit to consider is the audio frequency oscillator. This circuit is almost exactly the same as the low-frequency oscillator, except that the RC values have been changed so that it oscillates at a higher frequency, and the voltage divider circuit that sets the threshold voltage at the positive terminal (pin 5) is modified. The lower half of this voltage divider includes a transistor. As the transistor turns on, the resistance of the lower half of the voltage-divider is changed, and this will change the frequency of the audio oscillator. Thus, the pitch of the audio will increase and decrease at a rate set by the low-frequency oscillator.
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| − | </div>
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| − | Finally, we come to the power amplifier. This is a simple unity-follower op-amp, and its purpose is to drive the speaker and to isolate it from the audio oscillator. If the speaker were connected directly to the output of the audio oscillator, it would change the characteristics of that section, and we would not hear the siren effect.
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| − | </div>
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| − | The capacitor then smooths out the voltage. Without the capacitor, the output from the diode network would continually drop to zero, and then rise back up to its peak value. The capacitor averages this out, giving a smoothed DC value.
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| − | </div>
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| − | The next element in the circuit is an LM7805, a 5-volt linear voltage regulator. This can be replaced with similar devices to get different voltages (i.e., an LM7812 for 12V, an LM7809 for 9 volts, etc.). The LM7805 will output a steady 5 Volts as long as the input voltage is sufficiently high. The transformer should be chosen such that the voltage input to the regulator is not much higher than 5V (6V or 7V would be good). Excess voltage is dropped across the device's input and output terminals, and is converted to heat. The greater this voltage, the more heat the device has to dissipate. Since it can only dissipate a finite amount of heat, this in effect limits the amount of power this circuit can provide. Attaching a heat sink to the LM7805 will also help.
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| − | </div>
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| − | The circuit should be mounted in some sort of enclosure to protect the 120VAC input power terminals. The power terminals themselves should be wrapped in electrical tape or in heat shrink tubing for additional protection.
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| − | </div>
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| | {{ansreq|page={{#titleparts:{{PAGENAME}}|2|1}}|num=8f}} <!--T:75--> | | {{ansreq|page={{#titleparts:{{PAGENAME}}|2|1}}|num=8f}} <!--T:75--> |
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| | ==Nota histórica== | | ==Nota histórica== |
| | Esta especialidad se llamaba originalmente «Radio mecánica». El nombre fue cambiado a «Radioelectrónica» en 1956. | | Esta especialidad se llamaba originalmente «Radio mecánica». El nombre fue cambiado a «Radioelectrónica» en 1956. |
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| − | [[Category:Adventist Youth Honors Answer Book/es]]
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| | <noinclude></noinclude> | | <noinclude></noinclude> |
| | {{CloseHonorPage}} | | {{CloseHonorPage}} |
