PAGE 098 OF 150 · DISPLAYS & INDICATORS
VU Meter with LEDs
Audio level is shown as a moving bar.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Measuring sound level
A VU meter style display shows how loud audio is. The audio signal is rectified and smoothed into a changing voltage, which then drives a bar of LEDs.
Key points
- Use fast attack and slow decay in the smoothing circuit so peaks are visible.
- The LM3915 lights LEDs in steps of 3 dB, covering about 30 dB, which matches how we hear loudness.
- Colour the lowest LEDs green, the next yellow and the top red.
Line-level audio is around 1 V peak, so a small amplifier or divider may be needed to match your driver's input range.
REMEMBER
Loudness is logarithmic, so use a log-step driver for music.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.