• on Audio/Video/Photography
  • Published in issue 6/2014 on page 40
About the article


With a wide range and high resolution

An LED VU meter is an excellent tool for keeping a close eye on the magnitude of audio voltages and so help prevent an input from being overloaded, for example when used with a mixing desk or a guitar amp. The circuit described here has an exceptionally wide input range of 60 dB and a step size of 1 dB thanks to the use of 6 LM3915 driver ICs, which control a total of 60 LEDs.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component List
Default: 0.25 W 1%
R1 = see text and Table 2
R2 = 10kOhm
R3,R6,R9 = 820Ohm
R4a = 36kOhm
R4b,R7b = 2.4kOhm
R5,R8,R11 = 47Ohm
R7a = 9.1kOhm
R10 = 1.6kOhm
R12,R13,R14 = 680Ohm
P1–P6 = 100Ohm trimpot, horizontal
C1 = 1000µF 35V, low ESR, 5mm pitch, 13mm diam.
C2 = 10µF 16V, low ESR, 2mm pitch, 5mm diam.
C3 = 1µF 100V, MKT, 5mm pitch
C4 = 1nF, 5mm pitch
C5–C10 = 100nF, 2.5mm pitch
C11,C12,C13 = 22nF, 2.5mm pitch
B1 = DB101
D1–D50 = 10-element LED bargraph display, green, 10.16 x 25.40 mm
D51–D60 = 10-element LED bargraph display, red, 10.16 x 25.40 mm
IC1–IC6 = LM3915N
IC7 = LM7812 (TO220)
J1,J2,J3 = 2-pin pinheader, 0.1’’ pitch
6 pcs. DIP-20 IC socket for LED bargraph displays
6 pcs DIP-18 IC sockets for LM3915 Ics
PCB # 120698-1
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