Ultrasonic Sensor (HC-SR04)

• VCC: 5 V
• GND: Ground
• TRIG: Input — 10 µs HIGH to start a burst
• ECHO: Output — HIGH for echo time (µs)

Tip: Keep sensors away from soft/angled surfaces and from each other to avoid cross-talk.

Basic hookup to a microcontroller or Raspberry Pi (with divider on ECHO for 3.3 V logic).

Direct Timing (no library)

// HC-SR04 — direct timing
const int TRIG=9, ECHO=8;
void setup(){
  Serial.begin(115200);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
}
long readUS(){
  digitalWrite(TRIG, LOW); delayMicroseconds(3);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  return pulseIn(ECHO, HIGH, 30000UL); // timeout 30 ms (~5 m)
}
void loop(){
  long us = readUS();
  if(us==0){ Serial.println("No echo"); }
  else{
    float cm = us / 58.0;      // cm ≈ us/58
    float inches = us / 148.0; // in ≈ us/148
    Serial.print(cm,1); Serial.println(" cm");
  }
  delay(200);
}

Median Filter (smoother readings)

// Take N samples and return median (reduces outliers)
const int N=7;
long samples[N];
long medianUS(){
  for(int i=0;i<N;i++){
    samples[i]=pulseIn(8, HIGH, 30000UL); // after a trigger as above
  }
  // simple insertion sort
  for(int i=1;i<N;i++){ long k=samples[i]; int j=i-1; while(j>=0 && samples[j]>k){ samples[j+1]=samples[j]; j--; } samples[j+1]=k; }
  return samples[N/2];
}

Tip: For multiple sensors, trigger them sequentially with a small delay to avoid cross-interference.

Use a voltage divider on ECHO (e.g., 1 kΩ : 2 kΩ) to bring 5 V down to 3.3 V.

RPi.GPIO: Measure Distance

# sudo apt install python3-rpi.gpio
import time, RPi.GPIO as GPIO
TRIG, ECHO = 23, 24   # BCM pins
GPIO.setmode(GPIO.BCM)
GPIO.setup(TRIG, GPIO.OUT)
GPIO.setup(ECHO, GPIO.IN)

def ping_us():
    GPIO.output(TRIG, False); time.sleep(0.000003)
    GPIO.output(TRIG, True);  time.sleep(0.000010)
    GPIO.output(TRIG, False)
    t0 = time.time()
    while GPIO.input(ECHO)==0:
        if time.time()-t0>0.03: return 0
    start = time.time()
    while GPIO.input(ECHO)==1:
        if time.time()-start>0.03: return 0
    end = time.time()
    return (end-start)*1e6

try:
    while True:
        us = ping_us()
        if us==0: print("No echo")
        else: print(f"{us/58.0:.1f} cm")
        time.sleep(0.2)
finally:
    GPIO.cleanup()

pigpio (more precise timing)

# sudo apt install pigpio python3-pigpio
# sudo systemctl start pigpiod
import time, pigpio
TRIG, ECHO = 23, 24
pi = pigpio.pi()
pi.set_mode(TRIG, pigpio.OUTPUT)
pi.set_mode(ECHO, pigpio.INPUT)

def ping_us():
    pi.gpio_trigger(TRIG, 10, 1)  # 10 µs HIGH
    t0 = time.time()
    while pi.read(ECHO)==0:
        if time.time()-t0>0.03: return 0
    start = time.time()
    while pi.read(ECHO)==1:
        if time.time()-start>0.03: return 0
    end = time.time()
    return (end-start)*1e6

try:
    while True:
        us = ping_us()
        print("No echo" if us==0 else f"{us/58.0:.1f} cm")
        time.sleep(0.2)
finally:
    pi.stop()

ESP32/ESP8266 (Arduino core): TRIG can be 3.3 V. ECHO outputs 5 V — use a divider (e.g., 1 kΩ to GND, 2 kΩ to ECHO) or a logic shifter before connecting to the ESP pin.

ESP32: Read Distance

#include <Arduino.h>
const int TRIG=5, ECHO=18;  // ECHO must be level-shifted to 3.3V

long pingUS(){
  digitalWrite(TRIG, LOW); delayMicroseconds(3);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  return pulseIn(ECHO, HIGH, 30000UL); // ~5 m timeout
}
void setup(){
  Serial.begin(115200);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
}
void loop(){
  long us = pingUS();
  if(us==0) Serial.println("No echo");
  else      Serial.printf("%.1f cm\n", us/58.0);
  delay(200);
}

ESP8266: Read Distance

#include <Arduino.h>
const int TRIG=D5, ECHO=D6; // Level-shift ECHO to 3.3V

long pingUS(){
  digitalWrite(TRIG, LOW); delayMicroseconds(3);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  return pulseIn(ECHO, HIGH, 30000UL);
}
void setup(){
  Serial.begin(115200);
  pinMode(TRIG, OUTPUT); pinMode(ECHO, INPUT);
}
void loop(){
  long us = pingUS();
  Serial.println(us ? String(us/58.0,1) + " cm" : "No echo");
  delay(200);
}

ESP-IDF: Use gpio + rmt (receive) or a high-resolution timer to timestamp edges on ECHO; trigger using a 10 µs pulse on TRIG.

The HC-SR04 itself needs no drivers. If you use a USB-serial adapter for logging/control, you may need:

• CH341 Driver (GitHub)

Arduino

• Arduino Project Hub
• Arduino Playground
• Arduino IDE Download
• Install Arduino Libraries

Raspberry Pi

• Raspberry Pi Projects
• GPIO Zero Docs
• Raspberry Pi Docs
• Raspberry Pi Software
• Pi Getting Started

Espressif

• ESP-IDF Programming Guide (Official)
• Espressif Technical Docs / Datasheets
• ESP-IDF GitHub Repository
• PlatformIO + ESP-IDF
• Arduino Core for ESP32 (GitHub)

Drivers / Other

• CH341 Driver (GitHub)

Note: Environmental factors (temperature, airflow, surface angle/material) affect readings.

Important Notice For educational, prototype, experimental, laboratory and R&D use only. (non-RoHS)

WEEE

Not subject to WEEE marking; obligations apply to final equipment.

Manufacturer

Little Muffins Things Limited
166 River Heights, 90 High Street
London E15 2GQ
littlemuffinsthings.com

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