wirecraft

Smart Home · ESP32 DevKit

Fresh Air Sentinel

A ESP32 DevKit build with 4 components. Reads: Air sensor. Drives: OLED, LED, Buzzer. Warn with the buzzer when air quality drops past the threshold.

Open in the workbenchJump to code

4 parts · 11 connections · 9 steps

Wiring

Mini Map
power
ground
data
signal
analog

Parts

PartRefsQtyEst.
MQ-135 air quality sensorAirSensor1$2.20
SSD1306 OLED display (128×64, I²C)OLED1$3.20
LED (5 mm) + 220 Ω resistorLED1$0.15
Passive piezo buzzerBuzzer1$0.60
Plus: breadboard, jumper wires, USB cable≈ $6.15

Prices are rough hobby-market estimates. Click a part for wiring notes and specs.

Firmware

src/main.cpp
1// Air Quality Monitor
2// Generated by Wirecraft for the ESP32 DevKit (ESP32-WROOM-32)
3// Prompt: An air quality monitor with a gas sensor, OLED readout, warning LED and a buzzer for bad air
4//
5// Wiring, parts and step-by-step assembly live alongside this file.
6
7#include <Arduino.h>
8#include <Wire.h>
9#include <Adafruit_GFX.h>
10#include <Adafruit_SSD1306.h>
11
12#define AIRSENSOR_PIN 32
13#define LED_PIN 4
14#define BUZZER_PIN 5
15
16int airSensorAir = 0;
17Adafruit_SSD1306 oLED(128, 64, &Wire, -1);
18
19void setup() {
20  Serial.begin(115200);
21  if (!oLED.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { Serial.println(F("OLED not found")); }
22  oLED.clearDisplay();
23  oLED.setTextColor(SSD1306_WHITE);
24  oLED.setTextSize(1);
25  pinMode(LED_PIN, OUTPUT);
26  pinMode(BUZZER_PIN, OUTPUT);
27  Serial.println(F("Air Quality Monitor ready."));
28}
29
30void loop() {
31  // --- Read sensors ---
32  airSensorAir = analogRead(AIRSENSOR_PIN);
33
34  // --- React ---
35  // Warn with the buzzer when air quality drops past the threshold.
36  if (airSensorAir > 2200) {
37    tone(BUZZER_PIN, 880);
38  } else {
39    noTone(BUZZER_PIN);
40  }
41
42  // Refresh the display with live readings
43  oLED.clearDisplay();
44  oLED.setCursor(0, 0);
45  oLED.setCursor(0, 0);
46  oLED.print("Air sensor: "); oLED.println(airSensorAir);
47  oLED.display();
48
49  delay(50);
50}
51
platformio.ini
1; PlatformIO project for Air Quality Monitor
2[env:esp32dev]
3platform = espressif32
4board = esp32dev
5framework = arduino
6monitor_speed = 115200
7lib_deps =
8	adafruit/Adafruit SSD1306@^2.5.10
9	adafruit/Adafruit GFX Library@^1.11.9
10

Assembly

  1. 1

    Lay out your workbench

    Gather the ESP32 DevKit, a half-size breadboard, and a bundle of male-to-male jumper wires. Keep the parts list open — every component below gets its own spot on the breadboard. Don't plug in USB power until the last wire is placed.

  2. 2

    Seat the board and power rails

    Run a red jumper from the ESP32 DevKit's 3V3 (or VIN for 5 V parts) pin to the breadboard's + rail, and a black jumper from GND to the − rail. Every component's power and ground will tap these rails.

  3. 3

    Wire the Air sensor

    Place the MQ-135 air quality sensor on the breadboard. Power first: VCC → + rail, GND → − rail. Then signals: AOUT → GPIO32. Tip: Let it burn in for 24 h before trusting the numbers — the heater needs to settle.

  4. 4

    Wire the OLED

    Place the SSD1306 OLED display (128×64, I²C) on the breadboard. Power first: VCC → + rail, GND → − rail. Then signals: SDA → GPIO21, SCL → GPIO22. Tip: If nothing shows up, try I²C address 0x3D — some modules ship with it.

  5. 5

    Wire the LED

    Place the LED (5 mm) + 220 Ω resistor on the breadboard. Power first: CATHODE → − rail. Then signals: ANODE → GPIO4. Tip: The longer leg is the anode (+). The resistor can go on either leg.

  6. 6

    Wire the Buzzer

    Place the Passive piezo buzzer on the breadboard. Power first: GND → − rail. Then signals: SIG → GPIO5. Tip: Passive buzzers need tone(); active ones just want HIGH. This design assumes passive.

  7. 7

    Double-check before power

    Trace every wire against the diagram once more — 11 connections in total. The classic mistakes: swapped power and ground, and off-by-one rows on the breadboard. Thirty seconds of checking saves a component.

  8. 8

    Flash the firmware

    Open the exported folder in VS Code with the PlatformIO extension (free), plug in the ESP32 DevKit over USB, and hit Upload. PlatformIO fetches the libraries listed in platformio.ini automatically. Prefer the Arduino IDE? Copy src/main.cpp into a new sketch and install the same libraries from the Library Manager.

  9. 9

    Bring it to life

    Open the Serial Monitor at 115200 baud to watch live readings. Warn with the buzzer when air quality drops past the threshold. Adjust the thresholds at the top of the sketch to match your environment.