Monday, November 29, 2010

Electret microphone


An electret microphone is a type of condenser microphone, which eliminates the need for a polarizing power supply by using a permanently-charged material.

An electret is a stable dielectric material with a permanently-embedded static electric charge (which, due to the high resistance and chemical stability of the material, will not decay for hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. Electrets are commonly made by first melting a suitable dielectric material such as a plastic or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a permanent electrostatic "bias". Modern electret microphones use PTFE plastic, either in film or solute form, to form the electret.
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Read more by clicking here
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Electret

Electret (formed of elektr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885. Materials with electret properties were, however, already studied since the early 18th century. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy.

Read more at wikipedia by clicking here

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Loudspeaker










A loudspeaker (or "speaker") is an electroacoustic transducer that converts an electrical signal into sound. The speaker moves in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.

After the acoustics of the listening space, loudspeakers (and other electroacoustic transducers) are the most variable elements in a modern audio system and are usually responsible for most distortion and audible differences when comparing sound systems.

Driver design:
The most common type of driver uses a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move axially through a cylindrical magnetic gap. When an electrical signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the driver's magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical signal coming from the amplifier. The following is a description of the individual components of this type of loudspeaker.

Read more at wikipedia by clicking here
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Tuesday, November 23, 2010

Multivibrators



A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross-coupled by resistors and capacitors.

There are three types of multivibrator circuit:

astable, in which the circuit is not stable in either state—it continuously oscillates from one state to the other. Due to this, it does not require an input (Clock pulse or other).
monostable, in which one of the states is stable, but the other is not—the circuit will flip into the unstable state for a determined period, but will eventually return to the stable state. Such a circuit is useful for creating a timing period of fixed duration in response to some external event. This circuit is also known as a one shot. A common application is in eliminating switch bounce.
bistable, in which the circuit will remain in either state indefinitely. The circuit can be flipped from one state to the other by an external event or trigger. Such a circuit is important as the fundamental building block of a register or memory device. This circuit is also known as a latch or a flip-flop.
In its simplest form the multivibrator circuit consists of two cross-coupled transistors. Using resistor-capacitor networks within the circuit to define the time periods of the unstable states, the various types may be implemented. Multivibrators find applications in a variety of systems where square waves or timed intervals are required. Simple circuits tend to be inaccurate since many factors affect their timing, so they are rarely used where very high precision is required.

Before the advent of low-cost integrated circuits, chains of multivibrators found use as frequency dividers. A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency would accurately lock to the reference frequency. This technique was used in early electronic organs, to keep notes of different octaves accurately in tune. Other applications included early television systems, where the various line and frame frequencies were kept synchronized by pulses included in the video signal.


Read more about multivibrators at wikipedia by clicking here


Click here for another great article on multivibrators


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Tuesday, November 16, 2010

Logic Gates


A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic is called Boolean logic and is most commonly found in digital circuits. Logic gates are primarily implemented electronically using diodes or transistors, but can also be constructed using electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements.
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Click here to read more from the Wikipedia
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Click here to download a PDF that covers basic logic gates and there operation.
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Tuesday, November 9, 2010

Operational Amplifiers



An Operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals.
Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their origins in analog computers where they were used in many linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact that the characteristics of the final elements (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself.

If you are interested in reading more about op-amps I suggest downloading this 464 page PDF from Texas Instruments, "Op Amps For Everyone" , click here to download.
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You can also purchase the most current version of "Op Amps For Everyone" by clicking on the picture below.


For basic information on op-amps click here and here
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More books on op-amps:



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Dave Jones and the EEVblog


If you don't know who Dave Jones is I urge you to go check out his website http://www.eevblog.com/ and his YouTube page as well www.youtube.com/user/EEVblog
I think Dave's videos are some of the best on YouTube in my opinion, I find myself constantly checking to see when he has added a new one. Guaranteed to make you laugh and even teach you something as well, not to mention Dave's awesome product reviews.
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Monday, November 8, 2010

Electronics Certification



If you are interested in getting certified in the field of electronics these are a couple of my suggested places to get certified and in my opinion are far more current than other certification institutes like the ISCET for instance which is extremely outdated.

Expert Rating-
ExpertRating believes in delivering cutting edge competency evaluation and skills training services based on scientific testing and training methodologies through a quality driven approach. ExpertRating strives to continually improve and upgrade its services by adopting the latest technologies and methodologies in the development and delivery of testing and training services. Expert Rating has highly recognized electronics certifications. The test fees are extremely reasonable, but you must retest every year.

Click here to see all the electronics certificates that Expert Rating has to offer.


CETG(Consumer Electronics Technicians Group)-
The CETG is a group of technicians and electronics service professionals that have come together to help set a standard for knowledge and skill levels that need to be met by today's cosumer electronics repair men and women. We provide certification for both students and profesional technicians. Our certification let's employers and or customers know that you have completed the necessary steps to becoming a serious , knowledgeable technician that has an extensive undertanding of electronics and the skills to complete any electronics repair job properly and safely.

The CETG offfers three levels of certification:

Apprentice

Journeyman

Master Technician

Upon certification you will recieve a certificate and wallet card valid for five years.


Remeber to visit www.preher-tech.com for electronics repair and design information.

Saturday, November 6, 2010

Make Your Own Ring Tester


In this post I will share with you all the info you will need to make a homemade ring tester also called a FBT/LOPT tester, note FBT= Fly Back Transformer, LOPT= Line Output Transformer.
Although originally designed to test flyback transformers this tool is used more often today for checking the primary coil of SMPS transformers for shorted windings and also the primary and secondary windings of high voltage transformers found in inverter circuits along with many other high Q inductive components and of course I still check the occasional flyback which itself is a high voltage switching transformer.

Click here for the assembly manual for the original dick smith ring tester which is no longer in production. This manual includes a schematic and a parts list.
Below are some pictures of the beautiful ring tester my good friend Behzad made using the schematic and parts list from the included assembly manual.





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Tuesday, November 2, 2010

Monday, November 1, 2010

Testing Semiconductors



Click here to go to Samuel M. Goldwasser's webpage "Basic Testing of Semiconductor Devices" and learn his listed methods for testing diodes, transistors, darlington transistors, TRIACs, DIACs, digital transistors, SCRs and more.


Also come visit www.preher-tech.com for all kinds of electronics information.

The TRIAC



TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component which can conduct current in either direction when it is triggered (turned on), and is formaly named as bidirectional triode thyristor or bilateral triode thyristor.

A TRIAC is approximately equivalent to two complementary unilateral thyristors (one is anode triggered and another is cathode triggered SCR) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. It can be triggered by either a positive or a negative voltage being applied to its gate electrode (with respect to A1, otherwise known as MT1). Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, the holding current, such as at the end of a half-cycle of alternating current (AC) mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the control of very large power flows with milliampere-scale control currents. In addition, applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the TRIAC to the load.

Click here to read more about TRIACs

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The DIAC



The DIAC, or 'diode for alternating current', is a trigger diode that conducts current only after its breakdown voltage has been reached momentarily.

When this occurs, diode enters the region of negative dynamic resistance, leading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode. The diode remains "in conduction" until the current through it drops below a value characteristic for the device, called the holding current. Below this value, the diode switches back to its high-resistance (non-conducting) state. This behavior is bidirectional, meaning typically the same for both directions of current.

Most DIACs have a three-layer structure with breakdown voltage around 30 V. In this way, their behavior is somewhat similar to (but much more precisely controlled and taking place at lower voltages than) a neon lamp.

DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as TRIACs. Some TRIACs contain a built-in DIAC in series with the TRIAC's "gate" terminal for this purpose.

DIACs are also called symmetrical trigger diodes due to the symmetry of their characteristic curve. Because DIACs are bidirectional devices, their terminals are not labeled as anode and cathode but as A1 and A2 or MT1 ("Main Terminal") and MT2.

Click here to read more about DIACs


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