Ultrasonic STEM Component Pack

• Ultrasonic Sensor Module (HC-SR04)
• SG90 9g Micro-Servo + assorted servo horns
• Mounting hardware (standoffs/screws) + cable tie
• 2.54 mm jumper wires (multi-colour)
• Instruction Booklet (PDF + print)

• HC-SR04: VCC→5V, GND→GND, TRIG→D6, ECHO→D5 (Arduino example)
• SG90: Red→5–6V, Brown/Black→GND, Orange/Yellow→D9 (signal)
• Raspberry Pi: Level-shift or divide ECHO down to 3.3 V

Route wires to avoid fouling the servo horn; pause ~150–200 ms after each move before pinging.

Mount HC-SR04 to the bracket, attach the bracket to the SG90 horn, and connect as shown.

Scan + Distance (SG90 + HC-SR04)

#include <Servo.h>
Servo pan;
const int SERVO_PIN=9, TRIG=6, ECHO=5;

long pingUS(){
  digitalWrite(TRIG, LOW); delayMicroseconds(3);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  return pulseIn(ECHO, HIGH, 30000UL); // 30 ms timeout
}

void setup(){
  Serial.begin(115200);
  pinMode(TRIG, OUTPUT); pinMode(ECHO, INPUT);
  pan.attach(SERVO_PIN); pan.write(90); delay(500);
}

void loop(){
  for(int a=30; a<=150; a+=5){
    pan.write(a); delay(180);
    long us = pingUS();
    float cm = us ? us/58.0 : -1;
    Serial.print("A:");Serial.print(a); Serial.print("  cm:");Serial.println(cm,1);
  }
  for(int a=150; a>=30; a-=5){
    pan.write(a); delay(180);
    long us = pingUS();
    float cm = us ? us/58.0 : -1;
    Serial.print("A:");Serial.print(a); Serial.print("  cm:");Serial.println(cm,1);
  }
}

HC-SR04: Minimal Test

// TRIG→D6, ECHO→D5
void setup(){ Serial.begin(115200); pinMode(6,OUTPUT); pinMode(5,INPUT); }
void loop(){
  digitalWrite(6,LOW); delayMicroseconds(3);
  digitalWrite(6,HIGH); delayMicroseconds(10); digitalWrite(6,LOW);
  long us=pulseIn(5,HIGH,30000UL);
  if(us){ Serial.print(us/58.0); Serial.println(" cm"); } else { Serial.println("No echo"); }
  delay(200);
}

Use a divider/level shifter on ECHO. pigpio recommended for precise timing and servo pulses.

pigpio: Scan + Distance

# sudo apt install pigpio python3-pigpio
# sudo systemctl start pigpiod
import time, pigpio
PIN_SERVO=18; TRIG=23; ECHO=24
pi = pigpio.pi()
pi.set_mode(TRIG, pigpio.OUTPUT); pi.set_mode(ECHO, pigpio.INPUT)
def set_servo_deg(deg): pi.set_servo_pulsewidth(PIN_SERVO, int(500 + (max(0,min(180,deg))/180.0)*2000))
def ping_us():
    pi.gpio_trigger(TRIG, 10, 1)
    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
    return (time.time()-start)*1e6
try:
    for a in list(range(30,151,5))+list(range(150,29,-5)):
        set_servo_deg(a); time.sleep(0.18)
        us=ping_us(); print(f"A:{a}  cm:{(us/58.0):.1f}" if us else f"A:{a}  No echo")
finally:
    pi.set_servo_pulsewidth(PIN_SERVO,0); pi.stop()

• Voltage: ESP uses 3.3 V logic. Keep ECHO ≤3.3 V (divider/level shifter) if HC-SR04 is at 5 V.
• Servo power: Drive SG90 from 5–6 V with shared GND. Prefer ESP32 ledc PWM for smooth motion.

ESP32 (Arduino Core): HC-SR04 + Servo Scan

#include <Servo.h>
Servo pan;
const int SERVO_PIN=18, TRIG=22, ECHO=23; // adjust pins

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);
  pan.attach(SERVO_PIN); pan.write(90); delay(500);
}

void loop(){
  for(int a=30; a<=150; a+=5){
    pan.write(a); delay(180);
    long us = pingUS(); float cm = us ? us/58.0 : -1;
    Serial.printf("A:%d cm:%.1f\n", a, cm);
  }
  for(int a=150; a>=30; a-=5){
    pan.write(a); delay(180);
    long us = pingUS(); float cm = us ? us/58.0 : -1;
    Serial.printf("A:%d cm:%.1f\n", a, cm);
  }
}

ESP8266 (Arduino Core): Minimal HC-SR04

// TRIG->D6, ECHO->D5 (with divider to 3.3V)
void setup(){ Serial.begin(115200); pinMode(D6,OUTPUT); pinMode(D5,INPUT); }
void loop(){
  digitalWrite(D6,LOW); delayMicroseconds(3);
  digitalWrite(D6,HIGH); delayMicroseconds(10); digitalWrite(D6,LOW);
  long us=pulseIn(D5,HIGH,30000UL);
  if(us){ Serial.printf("%.1f cm\n", us/58.0); } else { Serial.println("No echo"); }
  delay(200);
}

ESP32: ledc PWM for SG90 (snippet)

// Use hardware PWM for stable servo pulses
const int SERVO_PIN=18, CH=0, FREQ=50, RES=16;
void setup(){
  ledcSetup(CH, FREQ, RES);
  ledcAttachPin(SERVO_PIN, CH);
}
void writeDeg(int deg){
  deg = constrain(deg, 0, 180);
  int us = 500 + (deg * 2000) / 180;      // 500–2500 µs
  int duty = map(us, 0, 20000, 0, 65535); // 20ms period -> 65535 @ 16-bit
  ledcWrite(CH, duty);
}

Notes: Keep cables clear of the servo sweep. Average multiple pings per angle if you need a smoother scan.

No PC drivers needed for the sensors/servo. If you use a USB-serial bridge during development:

• 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

Drivers / Other

• CH341 Driver (GitHub)

Note: Exact hardware mix may vary slightly by batch.

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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