KY-038 on OLED: Sound Level Meter
Overview & Wiring
What it is: The KY-038 (and near-identical KY-037) is a microphone module with an amplifier. Its analog output tracks sound level, so you can build a clap detector, noise meter, or sound-reactive light.
How it works: The electret mic feeds an op-amp; AO gives an audio-frequency signal riding on a mid-rail offset. To get a "loudness" number you sample AO quickly and measure the peak-to-peak swing over a short window. This sketch maps that swing to 0–100 %.
Wiring:
KY-038 AO -> GPIO0 (analog)
KY-038 VCC -> 3V3 (use "+" ; the module runs on 3.3–5V)
KY-038 GND -> GND
OLED VCC=3V3, GND=GND, SDA=GPIO4, SCL=GPIO5
Libraries: only "Adafruit SSD1306" and "Adafruit GFX Library".
On screen / Serial: a 0–100 sound level with a bar. Clap or talk near the mic.
Gotchas: Turn the onboard trimmer to set the amplifier gain — too high and it clips (stuck at 100), too low and it never moves. AO is an audio signal, not a steady voltage, so you must sample the peak-to-peak (as done here), not read it once.
Circuit Diagram
Parts You Need
Source Code (Arduino / ESP32)
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
#define MIC 0 // AO on GPIO0 (ADC)
void setup() {
Serial.begin(115200);
Wire.begin(4, 5);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
}
void loop() {
int hi = 0, lo = 4095;
unsigned long start = millis();
while (millis() - start < 40) { // 40 ms sampling window
int v = analogRead(MIC);
if (v > hi) hi = v;
if (v < lo) lo = v;
}
int pp = hi - lo; // peak-to-peak swing
int level = map(constrain(pp, 0, 3000), 0, 3000, 0, 100);
display.clearDisplay();
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.println("KY-038 Sound");
display.setTextSize(3);
display.setCursor(0, 18);
display.printf("%d", level);
display.drawRect(0, 54, 128, 8, SSD1306_WHITE);
display.fillRect(0, 54, map(level, 0, 100, 0, 128), 8, SSD1306_WHITE);
display.display();
Serial.printf("Sound: %d (pp %d)\n", level, pp);
}