Simple Volume Unit meter (VUmeter)
This is by far the simplest VUmeter you can build. It is
based on a single chip. A volume unit (VU) meter or
standard volume indicator is a device for displaying the level
of any voltage signal source (which is usually a sound signal).
the module to the output of any amplifier (or preamplifier)
and set the trimmer where all LEDs are lighting, when the volume
of the amp is at maximum (or at least at that point, where
you want all LEDs to light).
LM3915 is a very powerful and easy to find chip. It's a
monolithic integrated circuit that senses analog voltage levels
providing a logarithmic 3 dB/step analog display. With it, you
can drive LEDs, LCDs or even VFDs (Vacuum Fluorescent
In this circuit we use it as a VUmeter, driving 10
LEDs. Each time a new LED is lighting when the input voltage is
1.41 times the voltage, where the previous LED started to light.
This is exactly the point where the voltage is 3dB higher than
the previous one.
- One LM3915 chip.
- Ten 220Ù resistors (1/4 Watt).
- One 1.2KÙ resistor (1/4 Watt).
- One 10KÙ trimmer.
- One 100nF capacitor.
- (Optional) One 16ìF electrolytic
capacitor (16 Volts). Use it only if leads to the LED power
supply are 15cm o longer.
- One DC10SRWA LED Display by
(or ten separate red LEDs). You may use
different colors for the LEDs (e.g. green for lower and red for
- One 18pin socket for the chip.
- (Optional) A 20pin socket for the LED bar.
- One single row male pin header with 3 pins (If you have a
header with more pins, just cut it).
- A small piece of a Veroboard
- Wire for connections
- Solder and soldering iron
Also you will need a stabilized 12V external power supply. You
can power the VUmeter directly from the power source of the
amplifier (or preamp) providing the input signal (meaning
if the amp is also using a 12V supply).
Here is the schematic diagram of the simple VUmeter.
Note: The schematic is upside down, meaning the first
LED (that flashes at lower dBs) is the one connected to
pin 1 of LM3915.
Attention: Make sure you solder the 100nF capacitor as
close to LM3915 power supply pins as possible. The optional
electrolytic capacitor is required only if leads to the LED
supply are 15cm (about 6 inches) or longer. All 220Ù
resistors are used to limit LM3915 power dissipation and
Don't worry when the input voltage (signal) becomes negative.
LM3915 can handle negative (and positive) voltages up to
35V without damaging the chip.
You can use a precision full-wave
rectification circuit at the input, if you want a more accurate
In the following
pictures you see the circuit built on a piece of Veroboard.
And in this picture you see the simple VUmeter in action.