Distance sensor module (3.3 V safe)

The distance module is an HC-SR04 ultrasonic ranger with the 1 kΩ and 2 kΩ resistors that form the ECHO voltage divider already fitted, so the sensor's 5 V echo arrives at about 3.3 V. It costs $5.50 and is for distance sense: parking, level detection, presence, a robot's eyes. Wire vcc to 5 V, trig and echo to GPIOs and gnd to ground.

What's inside

Part	Qty	Price each
HC-SR04 distance sensor	1	$3
Resistor	2	$0.25
Total	3	$3.50

The HC-SR04 pings at 40 kHz and reports the round-trip echo time; it needs a 5 V supply and outputs a 5 V echo.
The 1 kΩ resistor is the top of the divider from ECHO, and the 2 kΩ resistor the bottom to ground — together they scale 5 V down to 3.33 V, a safe level for a GPIO.

Exposed pin	Inside the kit
vcc	`sonar:VCC`
trig	`sonar:TRIG`
echo	`r1:2`
gnd	`sonar:GND`

echo is the junction between the two resistors, not the raw ECHO pin, which is what makes the module 3.3 V safe. vcc must be 5 V; trig is a plain 3.3 V input. The kit has no chain ends.

Wiring it in circuit.py

circuit.py

from wiring import *

pi = Pi()
sonar = kits.DistanceModule()

pi.V5 >> sonar.vcc        # the HC-SR04 is a 5 V part
pi.GPIO23 >> sonar.trig
pi.GPIO24 >> sonar.echo   # divided to 3.3 V inside the kit
sonar.gnd >> pi.GND

Driving it in main.py

main.py

from gpiozero import DistanceSensor
from time import sleep

sonar = DistanceSensor(echo=24, trigger=23, max_distance=4)

while True:
    print(f"{sonar.distance * 100:.0f} cm")
    sleep(0.5)

Why buy the kit

Loose parts cost $3 + 2 × $0.25 = $3.50, against $5.50 — $2.00 for the divider fitted. That $2.00 is cheap insurance: feeding the raw 5 V echo into a GPIO is the HC-SR04's classic way to damage a Pi, and the module's divider ratio is already right. Building it by hand means choosing the two resistor values and remembering which one is the top half.

Simulator vs real hardware

gpiozero.DistanceSensor works unmodified: the simulator times the echo with the clock readings of the edges, so distances come out right even though the simulation advances in steps.
The speed of sound follows the zone temperature (~1.8 % faster at 30 °C than at 0 °C), and a ping that finds nothing in range gives a 38 ms echo, which the sensor reports as its maximum distance; leave at least 60 ms between pings, which sleep(0.5) comfortably does.
The datafeed's "missed echo" knob and the object's distance simulate angled and soft surfaces; the divider itself is exact, so there is no 5 V on the GPIO to detect.