Practice without theory is blind, theory without practice is useless. Edison.
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LED biasing.

It is certainly one of the most simple circuit to implement, but there are several questions that arise for newbies.

Normal LEDs work with 1.5V and a current of 10mA. Therefore we must calculate a resistance wich will be conected in series with the LED so that it takes the voltage exceeding the 1.5V that LED needs.

For instance, to drive a LED with a 5V power supply, the voltage drop across the resistor will be:
VRs = 5 – 1,5 = 3,5V          
and to obtain the resistance value we must divide this voltage drop by the current of 10mA that LED uses:
Rs = 3,5/10e-3 = 350 Ohm.

In the case of IR diodes and high brite white LEDs, is wise to choose one with a known part number, to see its features in a NTE manual or on their datasheets because their biasing current values ​​differ greatly from common LEDs.

Typical values ​​for infrared LEDs are:

Vf        Foward Voltaje                             1,3V/100mA
If         Continuos foward current             100mA

Typical values ​​for high brite white LEDs are:

Vf        Foward Voltaje                             3,2V
If         Continuos foward current             20mA
Is common in remote control transmitters the use of two IR diodes, this is done to increase the brightness of the transmitter and the angle of the IR beam. To polarize two diodes they can be connected in series. In this case we consider a resulting voltage:
1,3x2 = 2,6V           
and the same current for a single 100mA diode, since they are connected in series.

See the link to the white paper 5mm IR Diode IR333.

  See data sheets

Rythmic lights isolation.

A popular project among electronics enthusiasts, is the rhytmic lights. It is a very engaging and entertaining device, but we have to think about a very important consideration to design and build: the isolation of audio equipment. So we avoid a lethal risk.
Unlike a sequential light, the rhytmic lights box is connected to an external sound source and turn on lights with a small control voltage, the most suitable device for this purpose is the TRIAC. This component has no isolated control circuit from the "force" circuit. It has three pins: one of which, the Gate is to fire the TRIAC, another pin, the MT2, is one of the terminals of "force" and the third terminal, the MT1 is common for small trigger voltage and high voltage of "force" circuit. This terminal is normally connected to circuit ground terminal and to one of the electric home network. So depending on how you connect the mains plug, the earth can be connected to the phase (live) or neutral. In the first case the circuit ground is energized and through it the external audio source and any other device that is connected. Therefore there is a risk of electric shock when touching the ground line of our rhymic lights, the device housing, knobs and housing amplifier, equalizer, etc.
To eliminate this risk, we need to isolate electrically the rythmic lights from the audio source. There are several ways to do it:

1.    Use an audio transformer.

2.    Use a microphone to capture the audio from the environment for the rythmic lights.

3.    Using optical isolation with optocoupler or optotriac.
 1.    Audio Transformer: connect one of its windings to the rythmic lights and the other to the audio source, so it provides galvanic isolation.
It is hard to find it and not worth manufacture, as other solutions are inexpensive and simple. If transformer is connected as amplifier the audio signal is distorted, as a voltage reducer could be so small that it would not be enough to trigger the triacs. You can also burn the transformer if the power of the audio is very high. These problems can be solved by connecting a power resistor in the winding which is connected to the sound source and using operational amplifiers to amplify the signal in the winding that connects to the rythmic lights.

2.    Microphone: you can use a small electret microphone, they are very economical, but as the sign of a microphone is very small it must be amplified subsequently with operational amplifiers.

It has some practical drawbacks: it must obviously be in the ballroom, where the audio volume level is more than enough to work and can also be activated with the cries of the public. In addition, for some DJs is more convenient to install the equipment in a separate room from the ballroom where the audio level is not enough for the rythmic lights to work.

3.    Optical isolation: it is the choice that seems to me more efficient. The optical components are inexpensive and easy to get. We can use an optocoupler like 4N36 or even better an optotriac like MOC family.

With the optocoupler we are not isolatoing the audio from the rythmic lights board rather we are isolating the control stage from the power stage (force), typically implemented with TRIAC's. The optocoupler LED is part of the control stage and illuminates the phototransistor which is part of the power stage. To maintain isolation, of course, we must use separate voltage transformers and power supplies. However it is easier to get voltage transformers than audio transformers.


Electronic components stores in Santiago.(Chile)

Whenever we develop a medium or large project, most likely you need to resort to more than one store, because no any cover the entire spectrum of components that exist.

The stores are named next are wich I have visited personally and regularly for years.

Victronics, they has the largest stock of components . All semiconductors normally used by students in laboratory experiences and most used in the industrial area. You can also shop online. They have parking. 

Olimexhas few components, but has more modules and development boards, especially the popular Arduino. The Internet sales system works perfectly automatically reporting by email the state of the process.
Casa Royal has few components for design, also few to repair. They do have many devices and instruments at a good price.

RS is a global company that works with a supplier in England. There is everything. Components are requested by catalog and brought in 6-9 business days.

Casa Keim no great assortment of components for design, but they are the only ones with great range in power resistors and large printed circuit boards.

In the case of needing repair parts and schematic circuits for consumer equipment I prefer buying them from "Powerpuff Girls" at Digitel (phone 26324511), due to I'm not devoted to repair in this area, take the opportunity to ask them to guide me. They know all the typical failures of each model.
CM2 also specializes in components for repair. It's in "Galería Sur" of San Diego street (Santiago de Chile), but unlike the other premises of the gallery, is a big store, modern with a very complete stock.
In this gallery there are also several places to repair speakers.

Kowka specializes in electronic components to build electric guitar effects .

Digicom stock has not really updated, so they still keep old components that are already scarce.

Metacomhas all kinds of cables, sell by detail, audio, video, networking, etc. They have parking.
Fullalarms has control panels and sensors for home alarms at a good price. They have parking.

There is a store of industrial surpluses in Ñuble: Loetter. there are many transformers, motors, fans, radiators, contactors, variacs, instruments, etc. A good alternative for high-power components. There are also consumer line equipments in disarmament in the patio of the South Gallery.
And for those ingenuous who still believe that there is an electronic junk yard at "Carrascal" street, I regret to inform them that years ago a supermarket was installed.

If you need spares for electrical appliance, the best choice is to serch thru "Tenderinni" street with the original spare sample.