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Guest adyneamtu

Mică problemă vu metru LM3915

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Guest adyneamtu

Salut. Primul post pe acest forum dar m-am mai inspirat din proiectele de pe aici.


Asta e al doilea VU metru pe care-l realizez și am intalnit o mică problemă. Doresc să leg in cascada 2 sau mai multe IC-uri LM3915 folosind acest ghid si datasheet-ul integratului. Circuitul merge bine in modul bar dar la modul dot nu se aprinde un led.

Problema este că la trecerea dintre LED-ul 10 si 12 LEDul de la pinul 10 al primul 3015 ramane stins. Am tot cercetat si prin datasheet si pe google... nu gasesc raspuns. Atasez si schema facuta in circuit wizard. Aveți, vă rog, idee de ce nu se aprinde ?


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Guest adyneamtu

Aceeasi schema de conectare in cascada este prezentata si in datasheetul LM3915 paginile 9-11

Citez aici ce are legatura cu dot mode.

In order for the display to make sense when multiple LM3915s are cascaded in dot mode, special circuitry has
been included to shut off LED #10 of the first device when LED #1 of the second device comes on. The
connection for cascading in dot mode has already been described and is depicted below.
As long as the input signal voltage is below the threshold of the second LM3915, LED #11 is off. Pin 9 of
LM3915 #1 thus sees effectively an open circuit so the chip is in dot mode. As soon as the input voltage reaches
the threshold of LED #11, pin 9 of LM3915 #1 is pulled an LED drop (1.5V or more) below VLED. This condition is
sensed by comparator C2, referenced 600 mV below VLED. This forces the output of C2 low, which shuts off
output transistor Q2, extinguishing LED #10.
VLED is sensed via the 20k resistor connected to pin 11. The very small current (less than 100 μA) that is diverted
from LED #9 does not noticeably affect its intensity.
An auxiliary current source at pin 1 keeps at least 100 μA flowing through LED #11 even if the input voltage rises
high enough to extinguish the LED. This ensures that pin 9 of LM3915 #1 is held low enough to force LED #10
off when any higher LED is illuminated. While 100 μA does not normally produce significant LED illumination, it
may be noticeable when using high-efficiency LEDs in a dark environment. If this is bothersome, the simple cure
is to shunt LED #11 with a 10k resistor. The 1V IR drop is more than the 900 mV worst case required to hold off

LED #10 yet small enough that LED #11 does not conduct significantly. 



Avantajul circuit wizard e ca pot schimba tipul integratului. Am incercat si 3914 si 3916. Aceeasi problema apare. 

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Guest adyneamtu

Corectă observația. Chiar e posibil ca simularea sa nu fie corecta ?  Deocamdată ma pot baza doar pe simulare pana sosesc componentele din China. De-asta am si creat schema in circuit wizard, sa stiu de la bun inceput ce comand. Schema publicata mai sus e doar o mica parte din ceea ce voi realiza. Un VU metru va avea 30 de trepte si diferite jocuri setate prin combinatii de butoane. Folosesc 3 LM3915 pentru 30 de Leduri (10x3) si alte 4 LM3915 pentru 2 vu metre de cate 15 leduri.

Daca asta va persista problema si-n montajul real(doar 2 leduri care nu se aprind in varianta asta de schema) nu le voi mai conecta asa si ele vor ramane aprinse cand se trece la nivelul urmator, dar nu va arata prea bine.

Edited by adyneamtu
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Până îți sosesc piesele încearcă și cu alt simulator . (nu știu să recomand unul care modelează LM391x). Eu am pățit aberații în simulatoare consacrate , la scheme simple de tot . N-ar fi o minune să fie un bug și aici , dar nu pot afirma că e chiar așa. Oricum , fără să fiu un fan al VU-meter , am avut ocazia să văd funcționând astfel de scheme . Deci problema nu e nicicum la integrat - sau schema sau simularea . Succes !

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