Article
60-dB LED VU Meter
Most of the analogue audio media, including radio broadcasting, stick within 60 dB dynamic boundaries. This VU Meter was designed to be used as a desktop instrument with home audio appliances, so it has its own power supply. Driven by an AC musical signal taken directly from low impedance loudspeaker connectors, i.e. in parallel with loudspeakers, and having linear frequency response, it covers 60 dB dynamic range in 3 dB steps using 20 LEDs in a bargraph. Low component count and simplicity enable the circuit to be housed in a small box or behind a transparent shield like a small acrylic desktop photo holder.
Materials
Gerber file
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PCB
Extra info / Update
Due to a scaling error, the lower part of the circuit diagram is not visible. Components C5 and R7 should be connected to ground. The connections for S1 and S3 are on 3-way headers. The pole connection is at pin 3, not 2 as expected. Junction D21-C6-IC3 is erroneously labelled ‘+5V’. A suggested label is ‘V+’.
Component list
Resistors:
R1 = 2kOhm 7 (see text)
R2 = 10kOhm
R3 = 680Ohm
R4 = 22kOhm
R5 = 820Ohm
R6 = 2kOhm 2
R7 = 22Ohm
P1 = 100Ohm
Capacitors:
C1 = 1µ F 63V (MKS, MKC)
C2,C6 = 10µ F 16V radial
C4 = 2nF2 (see text)
C3,C7,C9 = 100nF
C5 = 22nF
Semiconductors:
IC1, IC2 = LM3915N
IC3 = LM7805
D1-D20 = LED
R1 = 2kOhm 7 (see text)
R2 = 10kOhm
R3 = 680Ohm
R4 = 22kOhm
R5 = 820Ohm
R6 = 2kOhm 2
R7 = 22Ohm
P1 = 100Ohm
Capacitors:
C1 = 1µ F 63V (MKS, MKC)
C2,C6 = 10µ F 16V radial
C4 = 2nF2 (see text)
C3,C7,C9 = 100nF
C5 = 22nF
Semiconductors:
IC1, IC2 = LM3915N
IC3 = LM7805
D1-D20 = LED
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