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Circuit Diagrams

Visual wiring reference for all five ESP32 sensor connections — passive component values, bus topology, and pull-up resistor placement.

DocumentDOC-01
MCUESP32-S3
BusI2C + Digital + ADC
Sensors6 covered
StatusAvailable
Wire Legend
3.3V GND SDA SCL Digital Analog Resistor Capacitor

MPU6050 — Gyroscope / Accelerometer

I2C · 0x68 · 3.3V · AD0 → GND sets address · Shared bus

I2C 0x68
ESP32 WROOM-32 3V3 GND GPIO 21 GPIO 22 MPU6050 VCC GND AD0 SDA SCL INT 3.3V RAIL GND RAIL AD0→GND = 0x68 4.7k 4.7k 100nF not connected
Using a breakout module? The blue PCB already includes the 4.7 kΩ pull-up resistors and 100 nF cap. You only need 4 wires: VCC, GND, SDA, SCL.

MAX30100 / MAX30102 — SpO₂ + Heart Rate

I2C · 0x57 · 3.3V · LED current spikes require a 10 µF bulk capacitor

I2C ⚠ 10µF
ESP32 WROOM-32 3V3 GND GPIO 21 GPIO 22 MAX30100/102 VIN/VCC VLED+ GND SDA SCL INT 3.3V RAIL VLED+ (30102) GND RAIL 4.7k 4.7k 100nF 10µF ⚠ not connected
⚠ 10 µF capacitor is critical. The IR and Red LEDs draw burst currents — without this cap, the 3.3V rail dips causing resets or corrupt readings. Place it as close to VCC as possible.

MLX90614 / HW-691 — IR Thermal Sensor

I2C · 0x5A · 3.3V · HW-691 breakout includes built-in pull-up resistors

I2C Pull-ups built-in
ESP32 WROOM-32 3V3 GND GPIO 21 GPIO 22 MLX90614 HW-691 Module VCC GND SDA SCL 4.7kΩ×2 built-in ✓ 3.3V RAIL GND RAIL 100nF
HW-691 module users: Only 4 wires needed — VCC, GND, SDA, SCL. For the bare TO-39 IC, add external 4.7 kΩ pull-ups. TO-39 pin order (flat up, anti-clockwise): Pin 1 = SCL, Pin 2 = GND, Pin 3 = SDA, Pin 4 = VDD.

Generic IR Sensor Module

Digital OUT · FC-51 / TCRT5000 / KY-032 · Verify supply voltage before wiring

Digital Check voltage!
ESP32 WROOM-32 3V3 GND GPIO 34 A) 3.3V MODULE — direct connection IR MODULE (3.3V type) VCC GND OUT OUT → GPIO34 direct B) 5V MODULE — voltage divider on signal wire IR MODULE (5V type) VCC (5V) GND OUT (5V!) 10kΩ 20k ≈3.3V → GPIO34
Identify 5V vs 3.3V: Check PCB silkscreen for voltage label. Modules with an LM393 comparator are usually 5V. A 5V signal direct to an ESP32 GPIO will damage the MCU over time.

LDR — Light Dependent Resistor

Analog ADC · GPIO35 · 10 kΩ voltage divider mandatory · No polarity

ADC · GPIO35 10kΩ divider
ESP32 WROOM-32 3V3 GND GPIO 35 3.3V RAIL LDR ☀ JUNCTION → GPIO35 10k GND RAIL 100nF (opt.)
The 10 kΩ resistor is mandatory. Without it GPIO35 floats and returns random ADC values. The LDR and 10 kΩ form a voltage divider — more light = lower LDR resistance = higher junction voltage = higher ADC reading.

A3144 — Hall Effect Sensor

Digital GPIO · GPIO25 · 5V supply · Open-collector output · Pull-up required

Digital · GPIO25 10kΩ pull-up 5V
ESP32 WROOM-32 5V / VIN GND GPIO 25 3V3 A3144 Hall Effect VCC (5V) GND OUT N S Magnet 5V RAIL GND RAIL 10k 3.3V pull-up OUTPUT → GPIO25 100nF
Open-collector output: A3144 OUT is active-LOW — it pulls to GND when a magnetic field is detected. The 10 kΩ pull-up to 3.3V ensures a defined HIGH state when no field is present. The sensor itself runs on 5V, but the 10 kΩ pull-up to 3.3V means the ESP32 GPIO reads 3.3V logic safely. Add a 100 nF decoupling cap between VCC and GND close to the sensor.