HS‑SR04 Ultrasonic

import sonar  # Controls the ultrasonic sensor
import time   # Controls pauses and timing

# Sets up the ultrasonic distance sensor
# pin26 to Trig corresponds to D2 on the Sensor Shield V5.0
# pin25 to Echo corresponds to D3 on the Sensor Shield V5.0

while True:  # Measure forever
    dist = sonar.Sonar(26, 25).checkdist()  # Fire the sound pulse and get the distance in cm
    print("Distance:", dist, "cm")  # Report the measurement to the PC
    time.sleep(1)  # One reading per second

Serial Monitor (move your hand toward the sensor bit by bit): 

Distance: 87.3 cm 

Distance: 42.1 cm 

Distance: 15.6 cm 

Distance: 7.9 cm 

💡 Note: the block builds the sensor fresh on every line like borrowing a brand-new measuring tape for each reading. Slightly wasteful, perfectly clear. Two physical limits to discover by experiment: wave your hand closer than 2 cm and the readings go crazy (the echo returns before the sensor is ready to listen!), and beyond 4 meters the echo is too weak. Every sensor has a comfort zone yours is 2 cm to 400 cm.

import sonar  # Controls the ultrasonic sensor
import time   # Controls pauses and timing

# Sets up the ultrasonic distance sensor
# pin26 to Trig corresponds to D2 on the Sensor Shield V5.0
# pin25 to Echo corresponds to D3 on the Sensor Shield V5.0

while True:  # Measure forever
    dist = sonar.Sonar(26, 25).checkdist()  # Measure the distance in cm
    print("Distance:", dist, "cm")  # Always show the raw number first
    if dist < 20:  # Closer than 20 cm?
        print("Zone: CLOSE almost touching!")  # Danger zone
    elif dist < 50:  # Between 20 and 50 cm?
        print("Zone: MEDIUM comfortable range")  # Warning zone
    else:  # Farther than 50 cm
        print("Zone: FAR all clear")  # Safe zone
    time.sleep(1)  # One reading per second

Serial Monitor: 

Distance: 71.2 cm 

Zone: FAR all clear 

Distance: 33.8 cm 

Zone: MEDIUM comfortable range 

Distance: 9.4 cm 

Zone: CLOSE almost touching! 

💡 Note: your zone funnel (12.2, 13.2, 16.2) now classifies distance and notice you chose the thresholds yourself. Why 20 and 50? Because zones should match a purpose: 20 cm is where a real robot must brake, 50 cm is where it should slow down. Thresholds are engineering decisions, not magic numbers change your mission, change your fences.

import sonar  # Controls the ultrasonic sensor
import time   # Controls pauses and timing

# Sets up the ultrasonic distance sensor
# pin26 to Trig corresponds to D2 on the Sensor Shield V5.0
# pin25 to Echo corresponds to D3 on the Sensor Shield V5.0

prev = 0  # Remembers: was the object close a moment ago? (0 = no)

while True:  # Watch forever
    dist = sonar.Sonar(26, 25).checkdist()  # Measure the distance
    now = 0  # Assume the object is NOT close right now
    if dist < 20:  # Is it inside the close zone?
        now = 1  # Then it IS close at this instant
    if now == 1 and prev == 0:  # Just ENTERED the zone!
        print(">>> ALERT: object detected!")  # The entry alarm
    if now == 0 and prev == 1:  # Just LEFT the zone
        print(">>> Object moved away. Clear.")  # The recovery message
    prev = now  # Save this state for the next comparison
    time.sleep_ms(200)  # Check 5 times per second

Serial Monitor (approach, hold, retreat, approach again): 

>>> ALERT: object detected! 

(nothing while you stay close...) 

>>> Object moved away. Clear. 

>>> ALERT: object detected! 

💡 Note: the entry/recovery pair your sixth deployment of the edge pattern, now guarding space instead of pins. Feel the difference from 19.2: the zone version repeats CLOSE forever; this version speaks once per event. A robot doesn't want to hear "wall! wall! wall!" every 200 milliseconds it wants one alarm per arrival so it can decide what to do without noise drowning its thoughts.

import sonar  # Controls the ultrasonic sensor
import time   # Controls pauses and timing

# Sets up the ultrasonic distance sensor
# pin26 to Trig corresponds to D2 on the Sensor Shield V5.0
# pin25 to Echo corresponds to D3 on the Sensor Shield V5.0

print("Get ready 5 readings in 5 seconds")  # Instructions
best = 999  # Starts impossibly FAR (lower = closer)
worst = 0   # Starts impossibly CLOSE (higher = farther)
total = 0   # The accumulator for the average

for i in range(1, 6, 1):  # Five readings: i counts 1..5
    dist = sonar.Sonar(26, 25).checkdist()  # One measurement
    print("Reading", i, ":", dist, "cm")  # Show each raw reading
    total += dist  # Add it to the running total
    if dist < best:  # Closer than anything so far?
        best = dist  # New closest record
    if dist > worst:  # Farther than anything so far?
        worst = dist  # New farthest record
    time.sleep(1)  # One second between readings

average = total / 5  # Normal division: decimals are welcome here
print("CLOSEST reading:", best, "cm")  # The min
print("FARTHEST reading:", worst, "cm")  # The max
print("AVERAGE distance:", average, "cm")  # The mean

Serial Monitor (wave your hand around during the 5 seconds): 

Get ready 5 readings in 5 seconds 

Reading 1 : 95.1 cm 

Reading 2 : 60.4 cm 

Reading 3 : 34.9 cm 

Reading 4 : 41.2 cm

 Reading 5 : 52.0 cm 

CLOSEST reading: 34.9 cm 

FARTHEST reading: 95.1 cm 

AVERAGE distance: 56.72 cm 

💡 Note: the best-so-far pattern worked twice at once closest (< against a huge start) and farthest (> against a zero start). Same skeleton, mirrored direction: that's what it means to own a pattern. And one tiny math upgrade: this program divides with / instead of //. The single slash keeps the decimals (56.72), the double slash would have thrown them away (56). Rulers need decimals; counters don't now you choose per mission.

import sonar  # Controls the ultrasonic sensor
import time   # Controls pauses and timing
# Sets up the ultrasonic distance sensor
# pin26 to Trig corresponds to D2 on the Sensor Shield V5.0
# pin25 to Echo corresponds to D3 on the Sensor Shield V5.0
sensor = sonar.Sonar(26, 25)

print("=== PARKING SENSOR ===")  # Mission title
print("Approach the wall slowly...")  # Instructions
while True:  # Park forever
    dist = sonar.Sonar(26, 25).checkdist()  # Measure the distance to the obstacle
    print("Distance:", dist, "cm")  # Always show the exact number
    if dist < 10:  # Danger zone: almost touching!
        print("########## STOP!!!")  # Full bar + alarm
    elif dist < 25:  # Getting close
        print("#######  CAREFUL")  # Long warning bar
    elif dist < 50:  # Medium distance
        print("####   approaching")  # Short bar
    else:  # Far away
        print("#      all clear")  # Tiny bar = safe
    time.sleep_ms(300)  # Refresh 3 times per second

Serial Monitor (the beeping you can SEE): 

Distance: 96.0 cm 

# all clear 

Distance: 44.2 cm 

#### approaching 

Distance: 21.7 cm 

####### CAREFUL 

Distance: 6.3 cm 

########## STOP!!! 

💡 Note: park an invisible object (a chair) and have a classmate find it using ONLY your screen if they can, your instrument works. Every element is old knowledge: zones (19.2), bars (12.5), fast refresh. New was only the design: four zones, four bars, one ladder. Notice the bar lengths are hand-drawn, not calculated fixed strings are simpler and just as convincing. In Level 2 this exact program gains a real buzzer whose beeps speed up as you approach... just like a real car.