A diagram showing an aphid feeding on a diseased plant and then moving to a healthy one
Generate stunning AI images like this one with Luraivin
![make the circuit diagram according to this Component Connected To ESP32 PinMultiplexer SIGA0 (Analog pin)MUX S0D0MUX S1D5MUX S2D6MUX S3D8MQ-2MUX Channel 0MQ-135MUX Channel 1LDRMUX Channel 2Sharp Dust Sensor OutputA3 (or D34)Sharp LED ControlD6 (you used it earlier)DHT11D7OLED I2C SDAD21OLED I2C SCLD22Power linesVIN → 5V, GND → GND +-------------------+ +----------------+ +-----------------+
| | | | | |
| MQ135 Sensor |----->| | | |
| (CO₂, VOCs) | | | | |
+-------------------+ | | | |
| | | |
+-------------------+ | | | |
| | | | | |
| MQ2 Sensor |----->| ESP32 |----->| OLED Display |
| (Smoke, LPG) | | (Microcontroller) | (128x64 I2C) |
+-------------------+ | | | |
| | | |
+-------------------+ | | | |
| |----->| | | |
| DHT11 Sensor | | | | |
| (Temp, Humidity) | +----------------+ +-----------------+
+-------------------+ # ESP32 Air Quality Monitor — Circuit Diagram & Detailed Wiring
**Project:** ESP32 Air Quality Monitor (MQ-2, MQ-135, Sharp dust, DHT11, LDR, OLED, 16‑ch MUX)
**Goal:** Clear, school-fair–ready circuit diagram and step‑by‑step wiring instructions so you can build the circuit reliably.
---
## 1) Summary of connections (as you requested)
| Component | Connected to ESP32 pin (D-label) |
| ----------------------------------- | ------------------------------------------------------: |
| Multiplexer SIG | A0 (Analog input) |
| MUX S0 | D0 |
| MUX S1 | D5 |
| MUX S2 | D6 |
| MUX S3 | D8 |
| MQ-2 | MUX channel 0 (SIG via channel 0) |
| MQ-135 | MUX channel 1 |
| LDR | MUX channel 2 |
| Sharp Dust Sensor analog output | A3 (or D34) |
| Sharp LED control (dust sensor LED) | **DO NOT USE D6** — see note below; use **D14** instead |
| DHT11 data | D7 |
| OLED SDA | D21 |
| OLED SCL | D22 |
| Power | VIN → 5V, GND → GND |
> **Important note:** You listed `MUX S2 -> D6` and also `Sharp LED control -> D6` which is a pin conflict. I have moved the Sharp LED control to **D14** in the detailed wiring so the MUX select lines are exclusive. If you want a different pin for the LED, you can change it later but **do not** leave both on the same pin.
---
## 2) Components & extra parts you will need
* ESP32 development board (DevKitC or similar)
* CD74HC4067 or 74HC4067 (16-channel analog multiplexer) **or** 4051 (8-channel) — wiring below assumes a 16‑channel device with S0..S3
* MQ-2 gas sensor module (module with analog output)
* MQ-135 gas sensor module (module with analog output)
* Sharp optical dust sensor (GP2Y1010AU0F or similar)
* DHT11 temperature & humidity sensor
* LDR (photoresistor) + 10k resistor for divider
* 2 × resistors for analog voltage dividers (10k + 20k recommended) for each 5V sensor analog output (see section 5)
* Jumper wires, breadboard, small perf board (optional)
* 0.1 µF decoupling caps (helpful) and a 10 µF capacitor for MQ modules (optional)
* USB cable and 5V supply / power bank (or power from VIN)
---
## 3) High-level Block Diagram (text/ASCII)
```
[MQ-135] --+
[MQ-2 ] --+--> [MUX channel inputs] -- SIG --> A0 (ESP32)
[LDR ] --+
[Sharp Dust Sensor] --> A3 (D34 on ESP32)
Sharp LED control --> D14 (ESP32)
[DHT11] --> D7 (ESP32)
[OLED 128x64 I2C] --> SDA:D21 SCL:D22
[MUX S0..S3] --> D0, D5, D6, D8 (ESP32)
Power: VIN->5V, GND->GND (common ground)
(All analog outputs that can reach 5V must be scaled to 0-3.3V before entering ESP32 ADC pins.)
```
---
## 4) Multiplexer wiring details
Wire the multiplexer as follows (example using CD74HC4067):
* VCC -> 5V (power the sensor side at 5V if modules need 5V)
* GND -> GND (common ground with ESP32)
* SIG (COM) -> **A0** (ESP32 analog pin)
* S0 -> D0 (ESP32)
* S1 -> D5 (ESP32)
* S2 -> D6 (ESP32)
* S3 -> D8 (ESP32)
* INH (enable/inhibit) -> GND (active low; tie low to enable)
**Channel mapping (example):**
* Channel 0 (S3..S0 = 0000) -> MQ-2 analog output
* Channel 1 (0001) -> MQ-135 analog output
* Channel 2 (0010) -> LDR analog divider output
* (Reserve other channels for future sensors)
Use the `selectMuxChannel(int channel)` function in your code to set S0..S3.
---
## 5) Protecting ESP32 ADC from 5V outputs (voltage divider)
Many gas sensor modules and the Sharp dust analog output can produce voltages close to 5V. ESP32 ADC input max is ~3.3V. Use a simple voltage divider for **each** analog sensor line that may reach 5V.
**Suggested divider (maps 0-5V to ≈0-3.33V):**
* Rtop = 10 kΩ
* Rbottom = 20 kΩ
Connection:
```
Sensor analog out ---- Rtop (10k) ----+----> ESP32 ADC pin
|
Rbottom (20k)
|
GND
```
This gives Vout = Vin * (20/(10+20)) = Vin * 0.666 → 5V -> 3.33V safe.
Use this divider on:
* MQ-2 analog out (before the MUX input)
* MQ-135 analog out
* Sharp dust analog out (if it can reach 5V)
> If your sensor modules are already 3.3V modules, you can skip the divider. Always measure with a multimeter first.
---
## 6) Sharp dust sensor special timing (LED pulse)
For Sharp GP2Y1010AU0F:
* Use the LED control pin from ESP32 (we assigned **D14**) to pulse the sensor LED.
* Typical timing (from datasheet):
1. Drive LED LOW (or HIGH depending on wiring) — follow your sensor’s module convention. In your existing code you used `digitalWrite(LED, LOW); delayMicroseconds(280); readAnalog(); delayMicroseconds(40); digitalWrite(LED, HIGH);` — this approach is OK if verified against your module.
2. Read analog value on A3 (D34) after the 280 µs delay.
***Important:*** Verify whether your sensor module expects active LOW or HIGH to turn on the internal IR LED. Test once with the datasheet and a brief code test.
---
## 7) DHT11 wiring
* VCC -> 3.3V or 5V (module supports both; if powering other sensors at 5V, you may use 5V)
* GND -> GND
* Data -> D7 (ESP32)
* If your DHT module has a pull-up resistor installed, you don’t need to add one. If not, add a 5k–10k pull-up between Data and VCC.
---
## 8) OLED wiring (I2C)
* VCC -> 3.3V (recommended for OLED I2C modules) or 5V per module docs
* GND -> GND
* SDA -> D21
* SCL -> D22
If the OLED is 5V-tolerant and you power it from 5V, ensure the SDA/SCL voltage levels are safe; otherwise power it from 3.3V and share ground.
---
## 9) Full wiring table (final)
| From | To | Notes |
| --------------------- | --------------------------------------------------------------------- | ---------------------------------------------------------------------- |
| MQ-2 analog out | MUX input pin for channel 0 (module side) — then SIG → A0 via divider | Use 10k/20k divider on the line feeding MUX if module outputs up to 5V |
| MQ-135 analog out | MUX channel 1 (same divider) | |
| LDR (voltage divider) | MUX channel 2 (read via SIG → A0) | LDR + 10k to form divider; output ~0-3.3V safe |
| MUX SIG (COM) | A0 (ESP32) | ADC input reads selected channel |
| MUX S0 | D0 | |
| MUX S1 | D5 | |
| MUX S2 | D6 | |
| MUX S3 | D8 | |
| Sharp dust analog | A3 (D34) via divider if needed | |
| Sharp LED control | D14 (ESP32) | Pulse according to datasheet timing |
| DHT11 data | D7 | |
| OLED SDA | D21 | |
| OLED SCL | D22 | |
| VCC for sensors & mux | VIN → 5V supply (or separate 5V regulator) | Common GND required |
| ESP32 GND | GND | Common ground for all modules |
---
## 10) Step-by-step breadboard build instructions
1. **Place ESP32** on the breadboard so pins are accessible.
2. **Place the multiplexer** (CD74HC4067) on the breadboard.
3. **Wire power rails**: connect 5V supply to VIN rail, connect ESP32 GND to ground rail.
4. **Connect MUX VCC/GND**: VCC→5V, GND→GND, INH→GND.
5. **Connect MUX SIG to A0** on ESP32 (SIG = COM pin).
6. **Wire MUX select pins**: S0→D0, S1→D5, S2→D6, S3→D8.
7. **Connect MQ-2**: module VCC→5V, GND→GND, Analog out→MUX channel 0 input pin (e.g., pin 0 on MUX). Add voltage divider between module analog out and MUX input if needed.
8. **Connect MQ-135** similarly to MUX channel 1.
9. **Connect LDR**: build an LDR divider (LDR + 10k) and connect its output to MUX channel 2.
10. **Connect Sharp Dust Sensor**: AO → A3 (D34) through divider; LED control → D14.
11. **Connect DHT11**: Data → D7, VCC→3.3V/5V, GND→GND. Add pull-up if needed.
12. **Connect OLED**: SDA→D21, SCL→D22, VCC→3.3V, GND→GND.
13. **Double-check all connections**, ensure no pins are shorted.
14. **Power up** the 5V supply and connect USB to ESP32.
---
## 11) Example MUX select function (code snippet)
```cpp
void selectMuxChannel(int channel) {
digitalWrite(MUX_S0, channel & 1);
digitalWrite(MUX_S1, (channel >> 1) & 1);
digitalWrite(MUX_S2, (channel >> 2) & 1);
digitalWrite(MUX_S3, (channel >> 3) & 1);
delayMicroseconds(5); // let signals settle
}
```
Call `selectMuxChannel(CH_MQ2)` then `analogRead(MUX_SIG_PIN)` to read that sensor.
---
## 12) Calibration & Testing tips
* **MQ sensors**: require a warm-up time (several minutes) and calibration in clean air. Use known concentrations if possible to map raw ADC to ppm.
* **Sharp dust**: map measured voltage to dust concentration using datasheet equation or module guide. Use the pulse-timing carefully.
* **LDR**: test in bright and dark light and record ADC ranges; you can normalize values in code.
* **ADC nonlinearities**: ESP32 ADC is non-linear and noisy. Use averaging (sample many times and average) and optionally apply calibration curves.
---
## 13) Safety & practical notes
* Do **not** feed >3.3V to ESP32 ADC pins. Use voltage dividers or level-shifting.
* Use a **common ground** for all modules and ESP32.
* Keep MQ modules ventilated during testing; they have heating elements.
* Use proper power supply rated for the current (MQ heaters draw current).
---
## 14) Troubleshooting checklist
* If a sensor reads 0 or constant: check wiring, confirm the MUX channel selection, measure the sensor analog out with multimeter.
* If readings are very noisy: sample multiple times and average, add small RC filters (0.1uF + resistor).
* If OLED shows garbage: check I2C address and wiring (SDA/SCL swapped?) and ensure correct voltage.
* If the ESP32 resets: check power supply current and VIN wiring.
---
## 15) What I couldn't draw here
I did a full textual electrical diagram and wiring table. If you want an actual image-style schematic (PNG/PDF) that you can print on chart paper or include in your science fair poster, tell me and I will generate a printable PDF schematic showing all wires laid out on a breadboard (I can produce a downloadable PDF next).
---
If you want the **exact printable schematic** (visual image or PDF), reply: **"Make printable schematic PDF"** and I will produce a downloadable file with the breadboard picture and clear labelled wires.](/_next/image?url=https%3A%2F%2Fluraivin-generated-images.s3.us-east-1.amazonaws.com%2Fimages%2F7939d984-4d7e-4141-9b18-252eefd1034d.jpg&w=3840&q=75)
