Ultrasonic Distance Sensor

This project measures the travel time of an ultrasonic pulse and converts it to distance. It introduces digital timing, sensor protocols, 5 V-to-3.3 V level protection, and filtering unstable readings.

Last updated July 15, 2026

Build Time: 50-75 minutes
Estimated Cost: $12-$20
Skill Level: Intermediate

Raspberry Pi PicoRaspberry Pi PicoUltrasonicSensorsTiming

Project illustration

A visual reference for this build. Use the parts, wiring, and instruction sections below for exact assembly details.

Recommended for

Middle School
High School
Adult Beginners
Homeschool

Skills

What You'll Learn

Trigger and time a digital sensor pulse
Convert pulse duration into distance
Protect a 3.3 V input with a voltage divider
Diagnose noisy or out-of-range measurements

Preparation

Required Parts

Gather these components before starting the build.

QuantityPartNotes

Qty: 1Raspberry Pi PicoMicroPython installed
Qty: 1HC-SR04 ultrasonic module5 V module
Qty: 11 kohm resistorEcho voltage divider
Qty: 12 kohm resistorEcho voltage divider
Qty: 1BreadboardHalf-size or larger
Qty: 6Jumper wiresMale-to-male

Wiring

Circuit Diagram

TRIG connects to GP3. ECHO reaches GP2 through a 1 kohm and 2 kohm divider so the 5 V echo signal is reduced for the Pico input.

Circuit overview

Pico ultrasonic sensor circuit. Follow the written connection notes and numbered build steps for exact wiring.

Build

Step-by-Step Instructions

Work through each stage in order and disconnect power before changing the wiring.

1. Power the sensor

Connect HC-SR04 VCC to 5 V, GND to Pico GND, and TRIG to GP3. Keep the system unpowered while building the echo divider.

2. Protect the echo input

Connect ECHO through 1 kohm to a junction connected to GP2. Connect 2 kohm from that junction to ground. Verify the divider before powering the circuit.

3. Run the measurement code

Point the sensor toward a flat object 10 to 50 cm away and run the program. Stable centimeter readings should appear four times per second.

4. Test the useful range

Move the target closer and farther away. Note where readings become unstable so your future project can reject unreliable values.

Programming

Project Code

Upload distance.py after completing the circuit.

distance.pypython

from machine import Pin, time_pulse_us
from time import sleep_us, sleep

trigger = Pin(3, Pin.OUT)
echo = Pin(2, Pin.IN)

def distance_cm():
    trigger.low()
    sleep_us(2)
    trigger.high()
    sleep_us(10)
    trigger.low()
    duration = time_pulse_us(echo, 1, 30000)
    return duration / 58.0

while True:
    try:
        print("{:.1f} cm".format(distance_cm()))
    except OSError:
        print("Out of range")
    sleep(0.25)