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uInvent 2011 – Concurs de electronica

May 31st, 2011 2 comments

Asociatia Studentilor din Electronica si Telecomunicatii organizeaza In colaborare cu Universitatea Maritima Constanta In perioada 28-30 iulie concursul international ľInvent -2011 destinat studentilor care au preocupari In domeniul design-ului electronic. Scopul concursului este de a crea ocazia informarii si schimbului de experienta Intre studenti si specialisti In domeniul electronicii, telecomunicatiilor si informaticii aplicate, ceea ce va contribui la dezvoltarea personala si profesionala a tinerilor participanti peentru o mai buna integrare pe piata muncii.

Detalii despre desfasurarea concursului
Prima categorie a concursului ľInvent -2011 o reprezinta realizarea de proiecte pe hardware-ul oferit de TexasInstruments. Acest hardware consta In kituri de dezvoltare EZ430-Chronos si eZ430-RF2500. Studentii maxim 2 In echipa, trebuie sa vina cu o idee de proiect ce se poate realiza pe unul din aceste kituri de dezvoltare la alegere In limita disponibilitatii.
Participantii vor completa o fisa de Inscriere care va contine detalii despre proiectul ce si-l propun sa Il realizeze. Fisa de inscriere va fi analizata de catre comitetul de evaluare si validare care decide daca proiectul este sau nu acceptat In concurs. In urma unei decizii favorabile organizatorii vor expedia kitul de dezvoltare catre participanti. Nu dorim sa restrictionam proiectele de aceea studentul poate face orice modificari doreste pe kitul de dezvoltare si poate folosi orice componente externe care considera ca Ii sunt necesare In vederea atingerii scopului propus. Atentie Insa, In cazul In care In urma modificarilor aduse kiturile de dezvoltare nu mai functioneaza, ASET nu garanteaza Inlocuirea acestora, deci eventualele modificari se fac pe propria raspundere.

In a doua categorie a concursului studentii se pot Inscrie cu proiecte pe care deja le-au realizat sau vor fi finalizate pâna la data desfasurarii concursului. Nu exista restrictii In aceasta categorie, studentii, maxim 2 In echipa, pot prezenta orice tip de proiect (cu conditia sa fie realizat de ei).
Cele doua categorii vor fi jurizate independent, vor avea premii separate iar un participant se poate Inscrie In ambele categorii cu precizarea ca nu poate prezenta acelasi proiect (software sau hardware).

Informatii utile pentru participanti
1. Fisa de Inscriere trebuie transmisa organizatorilor pâna la data de 15 Iunie, pe adresa contact@aset-web.ro
2. Confirmarea acceptarii proiectului propus: 16 Iunie 2011.
Kitul de dezvoltare va fi expediat viitorilor participanti imediat dupa confirmarea acceptarii propunerilor de proiect.
3. Pentru participarea la prima categorie a concursului ľInvent este obligatoriu ca In fisa de Inscriere sa fie mentionat cadrul didactic Indrumator, angajat al institutiei In care participantul studiaza.
4. Kitul de dezvoltare oferit de catre principalul sponsor TexasInstruments va fi transmis cadrului didactic Indrumator pe adresa institutiei de Invatamânt superior.
5. Nu se percepe taxa de participare.
6. Organizatorii asigura cazarea In perioada 28-30 iulie, mesele de prânz din zilele de 29 si 30 iulie si coffe-breaks pe durata desfasurarii evenimentului.
De asemenea participantii au la dispozitie gratuit mijloacele de transport de la locatia de cazare la sediul UMC unde se va desfasura concursul.

Pentru mai multe detalii vizitati www.aset-web.ro

Pitestiul de altadata

May 15th, 2011 No comments

Colaj realizat cu pozele Pitestiului de la 1915 … pe muzica ON THE BEACH AT WAIKIKI by Helen Louise and Frank Ferera 1915

TOATE DREPTURILE ASUPRA ACESTUI CLIP APARŢIN AUTORULUI. REPRODUCEREA INTEGRALĂ SAU PARŢIALĂ A CLIPULUI ESTE POSIBILĂ NUMAI CU ACORDUL PREALABIL AL ACESTUIA SAU PRIN PUBLICAREA LINK-ului http://www.youtube.com/watch?v=k5GZiAPRxC0 si a codului de incorporat.

Categories: serios Tags: , , ,

Compensarea sondei pentru osciloscop

May 15th, 2011 2 comments

… in continuarea acestui articol http://www.electronicstefan.ro/2011/03/sonda-osciloscop-testec-lf312/

Using simple wires to measure signals with the oscilloscope would result in unreadable plots on the scope, the main reason being the noise coupled onto the “probe” itself.
The first line of defense against that would be to use a coaxial cable as a probe, which would prevent external noise coupling. Unfortunately, an unwanted deterioration of the measured signal is achieved in this case, due to the capacitive loading that such a piece of cable adds to the signal. An equivalent schematic of an IC to IC signal is illustrated below:

equivalent schematic of an IC to IC signal

The non-zero output resistance of the signal source is modeled, as well as the input capacitance of the load. As it can be observed in the plot below, for a 2MHz square waveforms, both the signal at the output of the source and at the input of the load are practically identical:

both the signal at the output of the source and at the input of the load are practically identical

Things are different however, if you connect a 1x probe of an oscilloscope (which is basically a piece of coaxial cable) in an attempt to measure the signal. Due to the relatively large capacitance of the coaxial cable, an additional capacitive load is placed on the signal line. Assuming a 1 meter long probe, and taking into account that the capacitance of a coaxial cable is about 90pF/meter, the following equivalent schematic can show us the degradation of the signal (both at the load and measured on the scope):

quivalent schematic can show us the degradation of the signal

As it can be seen in the plot below, the non-zero output resistance of the signal source, together with the additional capacitance of the coaxial cable and that of the oscilloscope itself, form a severe RC filter which seriously deteriorates the signal on the line:

RC filter which seriously deteriorates the signal

Things become even worse if higher frequency signals are to be measured. For instance, trying to measure a 10MHz signal (so just 5 times higher frequency than in the previous example) in this manner will lead to seeing almost a triangle waveform on the oscilloscope:

triangle waveform on the oscilloscope

Attempts to reduce this effect have been directed towards decreasing the capacitance of the coaxial cable. Hence, actual oscilloscope probes are actually made of special coaxial cable, with very thin inner conductor, so that the equivalent overlapping surface between the inner conductor and the shield itself is decreased. In addition also the distance between the inner conductor and the shield itself increases, leading to smaller parasitic capacitance of the probe:

leading to smaller parasitic capacitance of the probe

This improvement alone does make things better, but it is not enough to make signals in the 10MHz range measurable. Compensated 10x probes must be used in order to accomplish reasonable measurements in this frequency.
The idea behind the 10x probe is to place a 9MegOhm series resistance in series with the tip of the probe. This configuration presents much higher impedance to the measured circuit, severely reducing the unwanted effects of the oscilloscope on the circuit itself. The entire effect of the oscilloscope input capacitance and that of the coaxial cable are virtually eliminated. Of course, the signal that reaches the oscilloscope itself is divided by a factor of 10, due to the resistive divider formed by this series resistor and the 1MegOhm input resistance of the capacitor; the scope itself however is capable of multiplying the actual measured signal by the same factor in order to display it correctly.
All these are true, however, for very low frequencies only. For higher frequencies, the 9MegOhm resistor together with the capacitance of the cable and that of the oscilloscope itself forms a real RC filter which literally kills off everything but the DC component of the measured signal. In order to prevent that, older designs of the 10x probes used to bypass the 9MegOhm series resistor with an adjustable capacitor (Cvar in the schematic below). This capacitor, together with the capacitance of the cable and that of the input of the scope would form a capacitive divider with the same 10:1.

divider with the same 10:1

As it may be seen from the plots below, the measurement of a 10MHz signal is greatly improved when using such a probe (when compared to the previous situation when the same signal was taken to the input of the scope with a 1x probe):

scope with a 1x probe

The actual signal reaching the scope itself is illustrated in blue in the plot above, and it may be seen that it is attenuated by a factor of 10. The oscilloscope can multiply this (either by internal amplification or through internal digital processing of the acquired samples) and display the correct result that would be identical to the green trace (the one the load of the signal sees too).
It is necessary for the bypass capacitor to be adjustable to allow for the matching of the probe to the various oscilloscope inputs. Sometimes, even for the same multichannel oscilloscopes, the input capacitance and resistance can be slightly different from channel to channel, so moving a probe from one channel to the other would involve slight adjustment of the bypass capacitor in order to reach the necessary capacitive divider ratio similar to that of the resistive divider. This adjustment is done by probing a known square wave signal and adjusting the Cvar capacitance until the signal displayed on the oscilloscope represents the expected shape of the signal. This is the process known as probe compensation.
Newer 10X probe designs have replaced the adjustable capacitor bypassing the 9MegOhm series resistor with a fixed one. This circuit is laser trimmed and has relatively low tolerances. For these probes, the compensation is done by adjusting a different variable capacitor which is placed in parallel to the oscilloscope input (Cvar in the schematic below) which is physically located at the end of the probe which connects to the scope. The purpose is the same: to obtain identical capacitive divider ratio to that of the resistive divider.

dentical capacitive divider ratio to that of the resistive divider

The advantage of such a construction is that you can still compensate your probe even if the tip of the probe is not accessible. For instance if you measure a DUT placed in a climatic chamber which keeps an inside temperature of +85Celsius, this ambient temperature will significantly alter the bypass capacitor of the 9MegOhm resistor. However, the tip of the probe being in the oven, the user cannot adjust that capacitor even if the probe would allow for that. However, the user can still adjust the variable capacitor at the other end of the probe so that it would match the new value of the bypass capacitor. As it can be seen from the plots below, the results are the same as with the previous type of 10x probe:

results are the same as with the previous type of 10x probe

Source: http://dev.emcelettronica.com/

:: Hai ca sunt in trend, de azi am si QR-code

May 14th, 2011 No comments

Poate va intrebati ce e ala QR-code ? Poate nu va intrebati !

Codul QR este o formă de bare bidimensionale sau cod matrice care a fost creat în 1994 de către japonezi Corporation Denso-Wave. Creatorii de cod au vrut să producă un decodor rapid şi, prin urmare, numele său “QR”(Quick Response), răspuns rapid. Deşi aceste coduri nu sunt utilizate în mod normal în multe părţi ale lumii în acest moment, acestea sunt foarte frecvente în Japonia, unde acestea sunt cea mai populară formă de bare bidimensionale.

Ele sunt utilizate cu regularitate în împreună cu telefoanele mobile pentru acces rapid la anumite site-uri pe net unde pot fi utilizate coduri pentru a stoca adrese URL sau adrese.

Un utilizator, cu software-ul cititor necesar şi un telefon cu camera, pot scana codul imagine pe care browser-ul telefoanelor il va redirecţiona către URL-ul în cauză. Simplitatea de a lega de lumea fizică în lumea electronica, cunoscut sub numele de “hyperlinkuri fizice” sau “hardlink” este esenţa codului QR şi explică popularitatea sa enormă. Un cod QR poate stoca un maxim de 7089 caractere numerice şi 4296 de caractere alfanumerice. Există două tipuri de QR-cod “Micro QR Code” şi “Design QR”.

Codul Micro QR este o formă mai mică de cod pentru utilizarea în cazul în care o capacitate mai mică de scanare. Codul de proiectare permite organizaţiilor să insereze imagini, logo-uri sau caractere în cod pentru a le face mai atrăgătoare şi uşor de recunoscut, fără nici o pierdere de informaţii. QR Codul este marcă înregistrată de către Denso Wave, Inc Codul QR este o modalitate de a obţine adresa URL a unui produs al unei companii fiind uşor de acceptat si folosit de un potenţial client. Acesta poate fi, de asemenea, uşor de recunoscut de către un client cu “Design QR”, care poate da un statut aproape de logo al firmei. Codul QR permite companiilor de a castiga noi potenţiali clienţi de la cei care sunt mai puţin pricepuţi in IT, sau celor care sunt leneşi atunci când vine vorba să tasteze adrese sau pentru cei care nu dispun de timp. Acesta devine foarte util atunci când adresele url sunt foarte lungi şi tastarea acestora într-un browser pe telefon mobil este anevoioasa.

qr_code_slidebar

Sursa: http://ro.wikipedia.org/wiki/

Categories: caterinca Tags: ,

Resistor color code calculator

May 11th, 2011 No comments

Acest program necesita Java SE Runtime Environment (JRE) http://java.sun.com/javase/downloads/index.jsp

Categories: electronica Tags: , , ,