Sound Level Meter

This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This circuit can also be integrated into audio amp projects.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 2.2uF 25V Electrolytic Capacitor C2, C3 1 0.1uF Ceramic Disc Capacitor R1, R3 2 1K 1/4W Resistor R2 1 10K 1/4W Resistor R4 1 100K 1/4W Resistor R5 1 1M 1/4W Resistor D1 1 1N914 Silicon Diode Q1 1 2N3906 PNP Transistor LED1-LED10 10 Standard LED or LED Array U1 1 LM3915 Audio Level IC MISC 1 Board, Wire, Socket For U1

Notes

1. V+ can be anywhere from 3V to 20V.
2. The input is designed for standard audio line voltage (1V P-P) and has a maximum input voltage of 1.3V.
3. Pin 9 can be disconnected from +V to make the circuit use a moving dot display instead of a bar graph display.
4. Thanks to help from the forum, this circuit has been improved from the original version to include a peak detector for a more stable and viewable output. This page has been updated with the new circuit.