Sound Pressure Level (SPL) Meter
the king-sized model
Published in issue 314, October 2002
The measuring instrument described here distinguishes itself in one respect from all the others in its species. The display has been implemented in such a way that is – without exaggeration – not easily overlooked. This opens up entirely new possibilities for its application.The most salient feature of this circuit is that the display consists of a panel made from 10 incandescent lamps. This immediately catches the eye, and at the same time it is obvious that we’re dealing with a novel kind of measuring instrument. A typical sound pressure or VU meter makes use of a much more modest LED or moving coil indicator.
Resistors:
R1,R9 = 10kΩ
R2 = 220Ω
R3 = 27kΩ
R4,R7 = 100kΩ
R5 = 3kΩ9
R6 = 3kΩ3
R8 = 39kΩ
R10 = 5kΩ6
R11 = 220kΩ
R12,R13,R14 = 10kΩ0
R15,R16 = 20kΩ0
R17 = 47kΩ
R18 = 1kΩ00
R19 = 30kΩ9
R20,R21 = 820Ω
R22-R31,R34 = 100Ω
R32 = 1kΩ2
R33 = 470Ω
R35 = 4Ω7
R36 = 2kΩ7
P1 = 500kΩ preset
P2 = 500Ω preset
Capacitors:
C1,C2 = 22µF 40V radial
C3,C14 = 470µF 16V radial
C4 = 15pF
C5 = 56nF, lead pitch 5mm
C6 = 2n7, lead pitch 5mm
C7 = 4n7, lead pitch 5mm
C8 = 8n2, lead pitch 5mm
C9 = 10 n, lead pitch 5mm
C10,C11 = 2µF2 63V radial
C12 = 100nF
C13 = 100nF, lead pitch 5mm
C15 = 1000µF 6V3 radial
C16 = 470µF 10V radial
C17 = 10µF 63V radial
C18 = 470µF 25V radial
Semiconductors:
D1-D10 = LED, red (no highefficiency type)
D11 = 1N4148
D12 = BAT85
D13 = LED, green (high-efficiency)
IC1 = TLC274
IC2 = TLC272
IC3,IC4 = LM3915
IC5...IC14 = S202S02 (Sharp)
IC15 = 7808
Miscellaneous:
JP1 = 2-way pinheader w. jumper
JP2 = 3-way pinheader w. jumper
K1-K11 = 2-way PCB terminal block, lead pitch 7.5 mm
K12 = cinch socket, chassis mounting
Tr1 = 9V 4VA8 e.g., Gerth 421.09
B1 = B80C1500 in rectangular case (80V piv, 1.5A peak)
F1-F10 = fuse, 500mA, fast, with PCB mount holder
MIC1 = MCE2000 (Monacor/Monarch) or equivalent
F11 = fuse, 32 mA, slow, with PCB mount holder
PCB, order code 020122-1
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Click below to download a PDF copy of this article from Elektor magazine. Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.
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