Ultrasonic distance sensor (HC-SR04) in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the HC-SR04 ultrasonic distance sensor?

The HC-SR04 sensor measures the distance to an object by sending ultrasonic sound waves and calculating the time it takes for the echo to return.

beginner

Which two pins on the HC-SR04 sensor are used to trigger and receive the ultrasonic pulse?

The 'Trig' pin sends the ultrasonic pulse, and the 'Echo' pin receives the reflected pulse to measure distance.

intermediate

How do you calculate distance from the duration of the echo pulse in Arduino code?

Distance (cm) = (duration of echo pulse in microseconds) / 58. This formula converts the time into centimeters.

beginner

What Arduino function is used to measure the duration of the echo pulse?

The function 'pulseIn()' measures the time in microseconds that the echo pin stays HIGH, representing the echo duration.

intermediate

Why do we need to set the Trig pin LOW before sending a HIGH pulse?

Setting the Trig pin LOW first ensures a clean HIGH pulse of 10 microseconds, which triggers the sensor correctly without noise.

What is the typical duration of the HIGH pulse sent to the Trig pin to start a measurement?

A 10 microseconds

B 1 millisecond

C 100 microseconds

D 1 second

The HC-SR04 sensor requires a 10 microsecond HIGH pulse on the Trig pin to start the ultrasonic burst.

Which Arduino function reads the time the Echo pin stays HIGH?

A pulseIn()

B digitalRead()

C analogRead()

D delay()

pulseIn() measures the length of a pulse on a pin in microseconds, perfect for reading the Echo pin duration.

If the echo duration is 1160 microseconds, what is the approximate distance in centimeters?

A 100 cm

B 58 cm

C 10 cm

D 20 cm

Distance = duration / 58, so 1160 / 58 = 20 cm approximately.

What does the Echo pin output when no object is detected within range?

A Constant HIGH

B Random HIGH and LOW

C Constant LOW

D Pulses at 1 kHz

If no echo is received, the Echo pin stays LOW because no reflected pulse returns.

Why is it important to wait some milliseconds between measurements?

A To avoid sensor overheating

B To allow the echo pulse to finish and avoid interference

C To save battery power

D To reset the Arduino

Waiting ensures the previous echo pulse is complete and prevents overlapping signals that cause wrong readings.

Explain how the HC-SR04 sensor measures distance step-by-step.

Think about sending a sound wave and timing its return.

Describe how you would connect and program the HC-SR04 sensor with an Arduino to measure distance.

Focus on wiring and the main code steps.