Introduction: Arduino RMS Meter Module

About: Design of classic audio test equipment.

This is a small Arduino module for measuring TrueRMS voltage. The meter displays the rms voltage in mV with digits and an analog level scale.

The module is intended as a "build in" module for monitoring a signal.

Step 1: Specifications and Parts


  • Bar-graph / Digital readout.
  • Specifications: Vrms: 50mV -> 1000mV
  • Freq: 20Hz – 20kHz
  • Input Impedance: 50 kohm

Dimension: 30x30x30 mm – display frame 3D printed

Arduino sketch: 3794b / 46% - 141b / 28%

Main parts:

  • ATtiny85 (DIL)
  • TLE2071 (OpAmp)

Step 2: Circuit Diagram

The design is build with an input circuit for correct signal level for the Arduino.

This is designed by a virtual ground level of 2V5. This is needed for the analog input and correct signal measurement.

The op-amp also improve the input impedance. The overall gain is 0dB.

Step 3: Arduino Code