Sound sensor¶

The KY-038 sound module (or similar LM393-based board) lets the ESP32 "hear" its surroundings: continuous level on the analog output, plus a digital comparator that fires when the sound crosses a tunable threshold. Great for clap detection, "clap-on" lamps, VU meters, or voice-activated triggers.

Description¶

On the module you'll find an electret condenser microphone — a small capsule whose diaphragm vibrates with sound pressure. An LM393 comparator amplifies the signal and compares it against a threshold set by the on-board pot.

The module exposes two signals:

• AO (Analog Out) — voltage proportional to sound intensity in real time. Useful for VU meters, level logging, proportional triggers.
• DO (Digital Out) — 0 when the sound crosses the threshold, 1 while quiet (active LOW). Useful for on/off alarm-style detection.

Components¶

Wiring¶

    ESP32                Sound sensor
    3.3V ──────────── VCC
    GND ───────────── GND
    GPIO 34 ◄────────── AO  (analog)
    GPIO 35 ◄────────── DO  (digital)

Code¶

from machine import Pin, ADC
import time

# --- Setup ---

ao = ADC(Pin(34))
ao.atten(ADC.ATTN_11DB)          # full 0-3.3 V range

do = Pin(35, Pin.IN)             # module's digital output

# Software threshold for AO (0-4095). Calibrate to your room's quiet level.
ANALOG_THRESHOLD = 2500


def read_sound():
    """Return (analog_level, noisy_flag)."""
    level = ao.read()
    # DO is active LOW: 0 = sound above the pot's threshold
    digital_noise = (do.value() == 0)
    return level, digital_noise


print("Sound sensor running. Ctrl+C to stop.\n")

while True:
    try:
        level, noisy = read_sound()
        analog_noise = level > ANALOG_THRESHOLD

        flag = ""
        if noisy or analog_noise:
            flag = "  [NOISE]"

        print(f"AO = {level:4d}   DO = {'LOW (sound)' if noisy else 'HIGH (quiet)'}{flag}")
        time.sleep_ms(50)
    except KeyboardInterrupt:
        print("\nStop.")
        break

Run the script¶

1. Assemble the circuit: VCC to 3.3V, GND to GND, AO to GPIO 34, DO to GPIO 35.
2. In Thonny, paste the code and press Run (F5).
3. Clap once — the console shows something like:

AO =  812   DO = HIGH (quiet)
AO =  834   DO = HIGH (quiet)
AO = 3902   DO = LOW (sound)  [NOISE]
AO = 4061   DO = LOW (sound)  [NOISE]
AO = 1284   DO = HIGH (quiet)

Calibration¶

Digital threshold (on-board pot)¶

Turn the blue pot on the module with a small screwdriver:

1. Make the room quiet.
2. Watch the second LED (DO / L1). In silence it should be off.
3. If it's on, rotate the pot (these are usually 10+ turn precision pots) until it goes dark.
4. Clap to test — the LED should blink with each sound.

Analog threshold (software)¶

Read AO with your room's background noise and set ANALOG_THRESHOLD to idle_value + 1500. Quick recipe:

# Average 50 readings during silence
samples = [ao.read() for _ in range(50)]
baseline = sum(samples) // len(samples)
print("Quiet:", baseline)
ANALOG_THRESHOLD = baseline + 1500

Example: blink LED on a clap¶

The onboard LED (GPIO 2) lights up for 1 second on every detected sound:

from machine import Pin, ADC
import time

ao = ADC(Pin(34)); ao.atten(ADC.ATTN_11DB)
do = Pin(35, Pin.IN)
led = Pin(2, Pin.OUT)

led_off_at = 0

while True:
    if do.value() == 0:                      # sound detected
        led.value(1)
        led_off_at = time.ticks_add(time.ticks_ms(), 1000)

    if led.value() == 1 and time.ticks_diff(led_off_at, time.ticks_ms()) <= 0:
        led.value(0)

    time.sleep_ms(20)

Example: clap-clap toggle¶

Toggle the LED only on two claps within a short window — the classic "clap-on" lamp:

from machine import Pin
import time

do = Pin(35, Pin.IN)
led = Pin(2, Pin.OUT)

last_clap = 0
state = False

while True:
    if do.value() == 0:                      # sound detected
        now = time.ticks_ms()
        if 100 < time.ticks_diff(now, last_clap) < 800:
            state = not state                # two claps in 0.1-0.8 s
            led.value(state)
        last_clap = now
        time.sleep_ms(200)                   # debounce — ignore echoes
    time.sleep_ms(10)

100 < dt < 800 rejects both close echoes (under 100 ms — the same sound firing twice) and long pauses (over 800 ms — uncorrelated claps).

Troubleshooting¶

Extension ideas¶

• Trigger a servo (Servo) on a clap — a lid that opens to sound.
• Drive an RGB LED color (RGB LED) by real-time sound level — green for quiet, red for loud.
• Web server with live level: extend the Temperature Web Server project, replacing the DHT22 read with an AO read.
• Remote clap detection: ship the events over ESP-NOW to a master board that counts claps across multiple rooms.

References¶

• MicroPython — machine.ADC reference
• LM393 datasheet (Texas Instruments)
• Random Nerd Tutorials — ESP32 Sound Sensor