Introduction: 2 Minute Ultrasonic Alarm

The ultrasonic sensor works by sending out sound waves and counting how long it takes for them to come back ( having been reflected from the nearest object.

In this circuit the ultrasonic sensor HC-SR04 plugs straight in to the Arduin, with pins 7 and 4 being used and GND and Vcc. The distance is calculated and every time the distance is less than a given threshold an alarm is raised, thus turning on an LED and a buzzer


•Arduino Uno

•5mm LED

•Piezo Buzzer

•Ultrasonic Sensor HC-SR04


chetancc (author)2014-11-12

Hi Robotix_au, I like ur instuctable very much. I programmed exactly d way u showed but my LED remains on after few seconds and serial monitor shows 0 cm continuously. Can u help me plz?

Robotix_au (author)chetancc2014-11-12

Unfortunately the HC-SR04 has horrible quality control. I throw away fully a quarter of the ones I buy. This is why the code has a safety feature of connecting GND first then VCC.

To test your sensor, I suggest you copy the code I have in the video below at around 6 minutes:

If it still shows 0, your sensor is busted :(

chetancc (author)Robotix_au2014-11-15

Many thx for the help and guidance Robotix_au Thx for ur time :)

MsSweetSatisfaction (author)2014-10-19

Neat little build! Thanks for sharing!

About This Instructable




Bio: I am robotics engineer and a teacher whose passion in life is breaking down the maths and academic jargon of programming and robotics into something ... More »
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