Analog Microphone

What it is

A microphone capsule, a transistor, and seven resistors and capacitors. The capsule is an electret microphone: a charged membrane with a tiny transistor of its own inside the can. The board's S8050 transistor amplifies what it hears, about 40 to 130 times from 5V depending on the part, and its output is SIGNAL.

Three things about it decide how a sketch should treat it. SIGNAL rests at a level set by the transistor's gain, anywhere from about 1.6 to 4.0 V from 5V, and sound makes it swing above and below that level, so a single reading means little: read the highest minus the lowest over 50 ms. Three 100 nF capacitors limit it to a band of roughly 75 Hz to 1 kHz, so it hears claps, knocks and loud voices, not quiet speech and not music. And a loud sound can take SIGNAL right up to VCC.

The page this replaces described an op-amp, an output centred at half the supply, and a level that rises with loudness. The board has no op-amp, its resting level is not half the supply, and a single reading does not rise with loudness.

Resting level and swing

The resting levels are worked out for the S8050's datasheet range, not measured. The swings are rough sizes from a comparable capsule's sensitivity, because this capsule's own is not published. Your numbers will differ; the gap between talking and a clap will not.

Which pin is which

Parts up, header at the bottom, reading left to right:

The back prints TK27 ANALOG MIC SENSOR instead of pin names. Turned over, the square pad is on the right, and it is still GND. There is no LED: test it by clapping and watching the swing.

Wiring, in three lines

1. GND to your board's GND.
2. VCC to 5V on an Uno, 3V3 on an ESP32, ESP32-S3 or Pico.
3. SIGNAL to an analog pin: A0 on an Uno, GPIO 34 on an ESP32, GPIO 4 on an ESP32-S3, GP26 on a Pico. On an ESP32, use an ADC1 pin so Wi-Fi does not stop the reading.

Leave NC unconnected.

Example

// The analog pin SIGNAL is wired to.
// Uno: A0. ESP32: 34. ESP32-S3: 4. Pico: 26.
const int MIC_PIN = A0;

void setup() {
  Serial.begin(115200);
}

void loop() {
  // Highest minus lowest over 50 ms: the swing, which grows with
  // loudness. The resting level cancels out of it.
  int lo = 32767;
  int hi = -1;
  unsigned long start = millis();
  while (millis() - start < 50) {
    int r = analogRead(MIC_PIN);
    if (r < lo) lo = r;
    if (r > hi) hi = r;
  }
  Serial.println(hi - lo);
}

import sys
import time
from machine import ADC, Pin

# The GPIO number SIGNAL is wired to. ESP32: 34. ESP32-S3: 4. Pico: 26.
adc = ADC(Pin(4))
if sys.platform == "esp32":
    adc.atten(ADC.ATTN_11DB)      # the full range, to about 3.1 V

while True:
    lo = 65535
    hi = 0
    start = time.ticks_ms()
    while time.ticks_diff(time.ticks_ms(), start) < 50:
        r = adc.read_u16()
        lo = min(lo, r)
        hi = max(hi, r)
    print(hi - lo)                # the swing: louder, bigger

Where to start

The handbook below is ten short articles, each with a working figure. The first reading is the whole build in three wires and a few lines, and resting level and swing turns it into one number that means something.

For something that reacts to a clap, a clap switch is the project. If the resting level puzzles you, the resting level works it out; if talking does nothing, three filters says why.