Parts · Sensors

Ultrasonic sensor (HC-SR04)

HC-SR04, the classic one: 5 V only

Measures distance with a sound too high to hear: it times the echo.

Ultrasonic sensor (HC-SR04) — Picture: Electrokit ↗

2Use it

The back of the two boards side by side. HC-SR04 (5 V): three chips, a 16-pin MAX232 (or no name), a 14-pin LM324 and a small 8-pin microcontroller. HC-SR04P (3.3 V and 5 V): one or two RCWL chips (or a CS100A) and the small M1 and M2 pads. Both have the pins VCC, Trig, Echo and Gnd. — Our drawing

Pin or leg	What it is for
VCC	+ 5 V
Trig	from a pin: starts a measurement
Echo	to a pin: the answer, at 5 V (into a Micro:bit through the divider)
GND	GND

Class rule, for every HC-SR04 of both kinds: VCC to 5 V, and Echo through the divider (1 kΩ from Echo to the pin, 2 kΩ from the pin to GND) or a level converter. Then you never need to know which kind you have.
Trig can go straight from a Micro:bit pin: 3.3 V is enough for both kinds.
On an Arduino (5 V pins) Trig and Echo go straight to two pins.
Point it at something flat and hard: soft things like a pillow give odd numbers.

Good to know: The 3.3 V kind (HC-SR04P) looks the same from the front, and sellers often print "HC-SR04" on it too. The back tells them apart: see the picture. On 3.3 V a classic one gives short, odd or no numbers.

The idea behind it, step by step: Ultrasonic distance sensor

Used in

Parking assist Parking gate

3Facts

Power	5 V only, about 15 mA
Range	about 2-400 cm
Pins	VCC, Trig, Echo, GND
On the back	three chips: a 16-pin MAX232 (or no name), a 14-pin LM324 and a small 8-pin microcontroller
On the front	almost always a small silver crystal (an oval can marked 4.000) between the two eyes

Kinds you may find

HC-SR04P (often printed "HC-SR04")	works on 3.3 V and 5 V: an RCWL or CS100A chip on the back, no MAX232. See "Ultrasonic sensor for 3.3 V"
RCWL-1601	works on 3.3 V too
US-016	gives the distance as a voltage on one pin

Where to buy

Electrokit ↗