#682 Electret Sound Detection Module

Reverse-engineering a commercial electret sound detection module intended for use with an Arduino/microcontroller as a sound level trigger (not audio pre-amp).

Build

Notes

I bought a Sound Detection Sensor Module some time back. Similar modules are available from many sellers on the usual marketplaces (aliexpress, ebay, taobao).

I don’t think I’d be the first to think I was buying an electret audio pre-amp module, only to discover they are actually configured as binary sound level triggers.

Basically, this means that when the sound level goes above a configurable threshold, the input will go from LOW to HIGH.

The input would usually be connected to a microcontroller GPIO and be used for sound-activated trigger event.

NB: see LEAP#681 for coverage of a legit Electret Audio Pre-amplifier.

Module Specs

As given by one of the sellers:

Features:

100% Brand new and high quality
Signal output indication
Single channel signal output
The output effective signal is low level
When there is sound, output low level and the signal lights
Can be used for Acoustic control light; give sound and light alarm working with Photosensitive sensor

Specifications:

Size: approx.32mm17mm15mm(lengthwidthheight)
Main Chip: LM393, Electret condenser microphone
Working Voltage: DC 4-6V
Color: Blue
Net Weight: 3g
Note: The Maximum induction distance is 0.5M

module

Circuit Design

Here’s my redrawing of the circuit. It basically comprises:

electret input ac-coupled to S9014 common emitter amplifier
amplified output (normally HIGH) is fed to inverting input of the LM393 comparator
10kΩ pot is used to set the comparator threshold (non-inverting input)
the signal output is pulled HIGH by default R6, but is normally LOW when insufficient sound to trigger
when the output is LOW, the green LED indicator will light
a red LED is power indicator

schematic

Behaviour

The output is a rail-rail digital signal, suitable for connection toe a GPIO pin of a microcontroller.

The threshold level would be set so that any sound over a certain volume would cause the output to toggle. It is possible to adjust for both output orientations:

adjust so normally output is high. Loud sound will cause the output to toggle high
adjust so normally output is low. Loud sound will cause the output to toggle high

The trace below captures the module output when exposed to a pure 1kHz sine wave input sound. With the threshold set at just the right level, and given the input is a pure sine wave, the output is a square wave oscillating at the same frequency for each phase of the sound wave that exceeds the threshold

scope

Credits and References