ESP32-S3 board
The brain that runs your uploaded sketch.
01 First, know the pieces
What you need
Six things, nothing more. Tap Define on any part you haven't met — the answer opens as a field note you can read and dismiss without losing your place.
GPIO extension board
Spreads the pins into rows you can reach and label.
HC-SR04 sensor
The distance sensor with two round transducers.
4 jumper wires
Temporary, solder-free connections.
Arduino IDE
Uploads code and opens Serial Monitor.
Official sketch
Sketch_19.1_Ultrasonic_Ranging.ino
02 Make the physical circuit
Chart the circuit
The official Freenove diagram is your chart. Click it to enlarge. Each connection below tells you where the wire goes and why it's there — hover a row to light it up.
VCC
→5V
Powers the ultrasonic sensor.
Trig
→GPIO 13
The board sends a short "start" pulse here.
Echo
→GPIO 14
The sensor returns a timed pulse here.
GND
→GND
Gives board and sensor the same zero point.
Check before power. Keep the sensor pins in the order printed on the module — VCC, Trig, Echo, GND — and unplug USB before you move any wire.
03 One action at a time
Build it
This is the main path — you can finish the day without opening a single field note. Tap each step as you go to keep your place.
0 / 7 done
Place the HC-SR04 so the two round transducers face outward, away from loose wires.
Connect
VCC → 5V,Trig → GPIO 13,Echo → GPIO 14, andGND → GND.Pause and compare your wiring to the chart before powering or uploading.
Open
Sketch_19.1_Ultrasonic_Ranging.inoin Arduino IDE.Upload the sketch to the ESP32-S3.
Open Serial Monitor and set the baud rate to
115200.Hold a flat object 10–30 cm in front of the sensor and move it slowly closer and farther.
04 Read just enough code
Read the code
You don't need the whole sketch today — just four lines that do the real work. Switch to MicroPython if you'd rather see the same idea in Python; the wiring never changes.
#define trigPin 13
#define echoPin 14
pingTime = pulseIn(echoPin, HIGH, timeOut);
distance = (float)pingTime * soundVelocity / 2 / 10000;#define trigPin 13Names GPIO 13 trigPin so the rest of the sketch reads plainly. pulseIn(echoPin, HIGH, timeOut)Times how long Echo stays HIGH — that's the raw measurement. … / 2 / 10000Sound goes out and back, so halve it; the / 10000 just lands the answer in centimetres. Optional side path · same circuit
trigPin = Pin(13, Pin.OUT, 0)
echoPin = Pin(14, Pin.IN, 0)Pin(13, Pin.OUT, 0)Sets GPIO 13 as the trigger output — the board's side of the ping.Pin(14, Pin.IN, 0)Sets GPIO 14 as the echo input — where the return pulse arrives.Same pins, same behaviour. Run it in Thonny and compare the printed distance with the Arduino version. If MicroPython isn't set up yet, skip this — it should never block the Arduino-first day.
05 Understand, don't memorise
Physics of a ping
The whole day is one loop, running many times a second. It's the same idea as counting the seconds between lightning and thunder.
Trig fires
Trig tells the sensor to emit a short pulse above human hearing.
It bounces
The pulse hits an object and some of it returns.
Echo holds HIGH
Echo stays HIGH for exactly the round-trip time.
Time → distance
Time × speed of sound gives how far the pulse travelled.
Useful model
distance = speed of sound × echo time ÷ 2
Why readings wobble
Real sensors react to object shape, angle, movement, and air. A little wobble is normal — watch the trend, not one number.
Why flat targets help
Flat objects bounce more sound straight back. Curved or soft ones scatter it, so the echo gets weaker.
06 Know it worked
Test & debug
Success and recovery sit side by side, so you never have to go hunting when something looks off.
What you should see
Distance: 24.31cmDistance: 23.92cmDistance: 24.08cm
A good reading changes when you move the object. Small wobble is fine.
If it doesn't
- 0 cm or frozen? Check Trig, Echo, GND, and the target's shape.
- Blank monitor? Confirm 115200 baud, then the board and port.
- Upload fails? Swap in a data-capable USB cable.
- Readings jump? Aim straight at a flat object.
07 Make the idea yours
Try this: a mini range log
Same working setup, one new skill: turning a measurement into a judgement. It fits inside today's 30 minutes.
Measure three targets
A book, a wall, and one object you pick. Note the expected distance, the reading, and anything odd.
Choose a threshold
Pick a "too close" distance — say 15 cm. Later that line can become a beep or a warning.
Logbook
08 Learn it with a hand on the tiller
Coach me through it
Every lesson ships with a code and a machine-readable packet, so an agent can guide you with full context.
Lesson code
TSK-DAY26-ULTRASONIC
Context packet
How the agent should behave: guide one physical step at a time, wait for you to confirm, explain terms on request, and always check wiring, board, port, and USB before changing code.