This is a stereo volume unit (VU) meter for audio equipment. It is a very useful device (basically in sound recording equipment) but you will love it because it also looks great!
The electronic circuit is based on the well known LM3915 IC which senses analog voltage levels and drives ten LEDs on a bar-graph, providing a logarithmic 3 dB/step analog display.
In our VU meter, we use 2 x LM3915 ICs, one for the Right (R) and another one for the Left (L) audio channel. We also use the MCP6022 – dual operational amplifier IC as a Precision Half-Wave Rectifier and Preamplifier.
The VU meter has two independent inputs, one for the Right (R) and another one for the Left (L) audio channel and there is one level adjust potentiometer in every input. The level-adjust potentiometer in every input enables the independent adjustment of the audio level in each audio channel. The circuit is able to accept any signal level and the minimum full-scale voltage level can be as low as 150mV. The input impedance in every channel is more than 33K.
The VU meter operates from a single supply as low as 3V or as high as 6V. The maximum supply current at full scale is about 350mΑ.
C3, R4, R5 and C5, R9, R11 adjust the rise and fall time for the L and R audio channel, respectively, acting as integrators. The VU-meter intentionally "slows" measurement, averaging out peaks and troughs of short duration. The “speed” of measurement is preset according to author’s preferences but can be easily set to another value. By replacing C3, R4, R5 and C5, R9 and R11 and after some trial and error you will be able to find the ideal values according to your preferences. Once a time, there were some standards for VU meters response but I think they mostly concern the case of old passive electromechanical devices.
The last thing I want to mention is to remember not to apply more than 6V in the power supply. The LM3915 withstands voltage up to 25V but the MCP6022 can not. If you forget this rule you will see your “unhappy” MCP6022 IC to start “smoking”…
Download the Stereo VU meter electronic schematic.
Download the PCB Artwork files for a small fee.