How to Use Sensors with Arduino and ESP32: Temperature, Distance, Load, Current, and Hall Effect

Introduction

Sensors are how microcontrollers perceive the physical world. From measuring room temperature with a $2 chip to weighing objects with a load cell, sensors turn physical quantities into electrical signals that Arduino and ESP32 can read, process, and act upon. This guide covers the five most useful sensor categories for maker projects: temperature and humidity, distance (ultrasonic), force and weight (load cells), current sensing, and magnetic field detection (Hall effect). For each sensor, you will learn the working principle, wiring, code, calibration, and practical applications.

What You Need

Arduino Uno/Nano or ESP32
Sensors: DHT22, HC-SR04, HX711 + load cell, ACS712, A3144/A1324 Hall sensor
Jumper wires and breadboard
Resistors, capacitors for signal conditioning as needed

Part 1: Temperature and Humidity (DHT22 / DHT11 / SHT30)

The DHT22 (AM2302) is the most popular combined temperature and humidity sensor for hobby projects. It provides digital output over a single wire, eliminating the need for analog calibration.

DHT22 Specifications

Temperature range: -40 to 80°C, ±0.5°C accuracy
Humidity range: 0-100% RH, ±2-5% accuracy
Sample rate: 0.5Hz (one reading every 2 seconds max)
Voltage: 3.3V to 6V

Wiring

VCC → 3.3V or 5V
GND → GND
DATA → Digital pin (with 10kΩ pull-up resistor between DATA and VCC)

Arduino Code

#include "DHT.h" #define DHTPIN 2 #define DHTTYPE DHT22 DHT dht(DHTPIN, DHTTYPE); void setup() { Serial.begin(9600); dht.begin(); } void loop() { delay(2000); // DHT22 needs 2 seconds between readings float h = dht.readHumidity(); float t = dht.readTemperature(); if (isnan(h) || isnan(t)) { Serial.println("Failed to read from DHT sensor!"); return; } Serial.print("Humidity: "); Serial.print(h); Serial.print("% "); Serial.print("Temperature: "); Serial.print(t); Serial.println("°C"); }

SHT30 (I2C Alternative)

The SHT30 is more accurate (±0.3°C, ±2% RH) and uses I2C, making it easier to wire and faster to read.

#include #include "SHTSensor.h" SHTSensor sht; void setup() { Wire.begin(); sht.init(); } void loop() { sht.readSample(); Serial.print(sht.getTemperature()); Serial.print("°C "); Serial.print(sht.getHumidity()); Serial.println("%"); delay(1000); }

Part 2: Distance Sensing (HC-SR04 Ultrasonic)

The HC-SR04 measures distance using ultrasonic pulses. It emits a 40kHz sound burst and measures the time until the echo returns.

Specifications

Range: 2cm to 400cm (claimed), realistically 2-300cm
Accuracy: ±3mm
Angle: 15° cone
Voltage: 5V (3.3V versions available as RCW-0001)

Wiring

VCC → 5V
GND → GND
Trig → Digital pin (output — triggers measurement)
Echo → Digital pin (input — receives echo timing)

Working Principle

Send 10μs HIGH pulse to Trig pin
Sensor emits 8 ultrasonic pulses at 40kHz
Echo pin goes HIGH when pulses are emitted
Echo pin goes LOW when echo is received
Duration of HIGH = round-trip time
Distance (cm) = (duration × 0.034) / 2

Arduino Code

const int trigPin = 9; const int echoPin = 10; void setup() { Serial.begin(9600); pinMode(trigPin, OUTPUT); pinMode(echoPin, INPUT); } void loop() { digitalWrite(trigPin, LOW); delayMicroseconds(2); digitalWrite(trigPin, HIGH); delayMicroseconds(10); digitalWrite(trigPin, LOW); long duration = pulseIn(echoPin, HIGH); float distance = duration * 0.034 / 2; Serial.print("Distance: "); Serial.print(distance); Serial.println(" cm"); delay(500); }

Pro Tips

Soft materials (fabric, foam) absorb sound — unreliable readings
Angles >15° cause missed echoes
Multiple sensors need staggered triggering to avoid cross-talk
Temperature compensation improves accuracy: speed of sound varies with temperature

Part 3: Force and Weight (HX711 + Load Cell)

Load cells measure force (and thus weight) by detecting tiny deformations in a metal beam using strain gauges. The HX711 is a 24-bit ADC amplifier designed specifically for load cells.

Load Cell Types

Single-point (platform scale): 1kg, 5kg, 10kg, 50kg — one cell supports the entire platform
S-type (hanging scale): Tension and compression, 50kg-5 ton
Button/pancake: Compression only, compact

Wiring

Load cell red → HX711 E+
Load cell black → HX711 E-
Load cell white → HX711 A+
Load cell green → HX711 A-
HX711 VCC → 5V (or 3.3V for 3.3V HX711 module)
HX711 GND → GND
HX711 DT → Digital pin
HX711 SCK → Digital pin

Arduino Code

#include "HX711.h" #define DT 3 #define SCK 2 HX711 scale; void setup() { Serial.begin(9600); scale.begin(DT, SCK); scale.set_scale(); // Calibrate later scale.tare(); // Zero with no load } void loop() { Serial.print("Reading: "); Serial.print(scale.get_units(), 1); // One decimal place Serial.println(" g"); delay(500); }

Calibration

Upload code with scale.set_scale() only (no calibration factor)
Tare (zero) with no load: scale.tare()
Place a known weight (e.g., 500g)
Note the raw reading
Calibration factor = raw_reading / known_weight
Update code: scale.set_scale(calibration_factor)
Verify with multiple known weights

Part 4: Current Sensing (ACS712 / INA219)

Current sensors let you monitor power consumption, detect motor stall, or implement overcurrent protection.

ACS712 Hall-Effect Current Sensor

Non-invasive: sensor sits in series with the load
Outputs analog voltage proportional to current
Versions: 5A (185mV/A), 20A (100mV/A), 30A (66mV/A)
Isolation: 2.1kV dielectric strength

Wiring

IP+ and IP- → Inline with the wire carrying current to measure
VCC → 5V
GND → GND
VOUT → Analog pin

Arduino Code (ACS712-5A)

const int sensorPin = A0; const float sensitivity = 0.185; // 185mV per A for 5A version void setup() { Serial.begin(9600); } void loop() { int raw = analogRead(sensorPin); float voltage = raw * (5.0 / 1023.0); float current = (voltage - 2.5) / sensitivity; // 2.5V = zero point Serial.print("Current: "); Serial.print(current, 2); Serial.println(" A"); delay(500); }

INA219 (I2C Current/Voltage/Power)

The INA219 is a digital current monitor with I2C output. It measures both bus voltage and shunt voltage, calculating current and power internally.

#include #include Adafruit_INA219 ina219; void setup() { ina219.begin(); } void loop() { float current_mA = ina219.getCurrent_mA(); float power_mW = ina219.getPower_mW(); Serial.print("Current: "); Serial.print(current_mA); Serial.print(" mA "); Serial.print("Power: "); Serial.print(power_mW); Serial.println(" mW"); delay(1000); }

Part 5: Hall Effect Sensors (A3144 / A1324 / DRV5053)

Hall effect sensors detect magnetic fields. They are used for position sensing, speed detection, current sensing, and brushless motor commutation.

Types

Digital (switch): A3144, 3144E — output HIGH/LOW when field exceeds threshold
Linear (analog): A1324, DRV5053 — output voltage proportional to field strength
Current transducer: Integrated with current path (ACS712 is a Hall current sensor)

A3144 Digital Hall Sensor

Used for endstops, door sensors, RPM counting, and magnetic switches.

Wiring

VCC → 5V
GND → GND
OUT → Digital pin (with 10kΩ pull-up to VCC)

Arduino Code

const int hallPin = 2; void setup() { pinMode(hallPin, INPUT_PULLUP); Serial.begin(9600); } void loop() { int state = digitalRead(hallPin); Serial.println(state == LOW ? "Magnet detected" : "No magnet"); delay(100); }

A1324 Linear Hall Sensor

Measures magnetic field strength for position sensing and joystick-like control.

const int hallPin = A0; void setup() { Serial.begin(9600); } void loop() { int raw = analogRead(hallPin); float voltage = raw * 5.0 / 1023.0; // Quiescent output is ~2.5V, sensitivity ~5mV/Gauss float field = (voltage - 2.5) / 0.005; Serial.print("Field: "); Serial.print(field); Serial.println(" Gauss"); delay(100); }

Sensor Selection Guide

ApplicationRecommended SensorInterfaceCost Room temp/humidityDHT22 or SHT301-Wire / I2C$3-5 Distance / levelHC-SR04Digital pulse$1-2 Weight / forceHX711 + 5kg load cellDigital$3-5 DC currentACS712-5A or INA219Analog / I2C$2-4 Magnetic switchA3144Digital$0.50 Magnetic field strengthA1324 or DRV5053Analog$1-3

Pro Tips

Averaging: Take 10-50 samples and average for noisy analog sensors
Shielding: Current sensors and Hall sensors are affected by nearby magnetic fields — keep away from motors and transformers
Decoupling: Add 100nF ceramic capacitor across sensor VCC/GND near the sensor for stable readings
Cable length: Keep sensor cables short; for long runs use shielded cable or digital sensors (I2C)
Calibration: Always calibrate load cells and current sensors with known references
Timing: DHT22 needs 2 seconds between readings; querying faster gives garbage data
Temperature compensation: Ultrasonic sensors and load cells drift with temperature — add a temperature sensor and compensate in software

Conclusion

Sensors transform physical phenomena into data your microcontroller can act upon. Temperature sensors monitor environments, ultrasonic sensors measure distance without contact, load cells weigh objects with precision, current sensors protect circuits and measure power, and Hall sensors detect magnets for position and speed. The common thread is proper wiring, appropriate libraries, calibration against known standards, and software filtering to handle real-world noise. With these five sensor types, you can build weather stations, automated scales, collision-avoiding robots, battery monitors, and magnetic position encoders.

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