Lesson 5 of 5

Distance with an HC-SR04

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// Measure distance and light LD2 when something is near const int TRIG_PIN = 7; // D7 = PA8 const int ECHO_PIN = 8; // D8 = PA9, 5 V tolerant, so ECHO goes in directly const long NEAR_CM = 20; // closer than this lights LD2 void setup() { pinMode(TRIG_PIN, OUTPUT); pinMode(ECHO_PIN, INPUT); pinMode(LED_BUILTIN, OUTPUT); Serial.begin(115200); } void loop() { digitalWrite(TRIG_PIN, HIGH); // a 10 µs pulse sends the burst delayMicroseconds(10); digitalWrite(TRIG_PIN, LOW); // ECHO stays HIGH for the round trip: 58 µs per cm long cm = pulseIn(ECHO_PIN, HIGH, 30000) / 58; bool near = cm > 0 && cm < NEAR_CM; digitalWrite(LED_BUILTIN, near ? HIGH : LOW); Serial.print(cm); Serial.println(near ? " cm NEAR" : " cm"); delay(100); }

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Measure distance with an ultrasonic sensor and light LD2 when something comes close. The sensor runs at 5 V, and its ECHO pin goes straight into D8, one of the Nucleo's 5 V tolerant pins.

Drag the object in the figure
ECHO goes to a digital pin: an ADC input in analog mode takes 4.0 V at most
Change the near distance and watch LD2

Pin	Connects to	What it does
`5V`	The sensor's VCC	The HC-SR04 needs 5 V.
`D7`	TRIG	Output: a 10 µs, 3.3 V pulse starts a measurement.
`D8`	ECHO	Input: a 5 V pulse, fine on this 5 V tolerant pin.
`GND`	The sensor's GND	Common ground.

Wire it in

Sensors and actuators this board drives, with the real connections.

HC-SR04 ultrasonic sensorSupply 5 V
VCC on 5V, TRIG on D7, ECHO on D8. D8 (PA9) is 5 V tolerant, so the 5 V echo needs no divider here.
Part pin Board pin
VCC 5VWire colour red
TRIG D7Wire colour yellow
ECHO D8Wire colour green
GND GNDWire colour black
Careful
Take ECHO to a digital pin, never to an input you read with analogRead(): in analog mode a pin takes 4.0 V at most.

All 8 parts on the STM32 Nucleo-F401RE page

Connects to

What it does

5V

The sensor's VCC

The HC-SR04 needs 5 V.

D7

TRIG

Output: a 10 µs, 3.3 V pulse starts a measurement.

D8

ECHO

Input: a 5 V pulse, fine on this 5 V tolerant pin.

GND

The sensor's GND

Common ground.

Wire it in

Sensors and actuators this board drives, with the real connections.

HC-SR04 ultrasonic sensorSupply 5 V

VCC on 5V, TRIG on D7, ECHO on D8. D8 (PA9) is 5 V tolerant, so the 5 V echo needs no divider here.

Part pin	Board pin
VCC	5VWire colour red
TRIG	D7Wire colour yellow
ECHO	D8Wire colour green
GND	GNDWire colour black

Careful

Take ECHO to a digital pin, never to an input you read with analogRead(): in analog mode a pin takes 4.0 V at most.

All 8 parts on the STM32 Nucleo-F401RE page

Distance with an HC-SR04

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Distance with an HC-SR04

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in