60-dB LED VU Meter

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eric

Posted: Sun Aug 27, 2006 10:19 am Post subject: 60-dB LED VU Meter

Site Admin Joined: 01 Jan 1970 Posts: 311

Rikard Lalic
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.
The LM3915 IC from National Semiconductor
senses voltage levels and drives 10 LEDs, providing a
logarithmic 3 dB/step analogue display, and so covering
a 30 dB range. LED current drive is programmable
and regulated. The IC contains adjustable voltage reference
source and an accurate 10-step 22-kΩ voltage
divider array. A ground referenced, ±35V-proof input
buffer amplifier, capable of sensing down to ground,
is driving 10 comparators referenced to the voltage
divider. Applying an additional

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