Ultrasonic proximity indicator (3 transistors)
This circuit along with ultrasonic sensor module HC-SR04 detects an object in front of it and gives a linear indication of the distance between the object and the sensor using output LED and a speaker. The speaker starts to make a sound when the object is 1m apart from the sensor as the object approaches nearer and nearer to the sensor the sound gets louder. This indicates that the intensity of sound is proportional to the distance between the object and the sensor. How HC-SR04 ultrasonic module works? The HC-SR04 sensor has one transmitter and one receiver. The transmitter produces ultrasound which has a frequency of 40KHz and therefore it's inaudible to human ears. The receiver is tuned to pick up ultrasound, as most of the objects reflect sound, the sound reflected back by the object in front of the sensor is detected by the receiver circuit. A signal proportional to the time it takes for sound to reach the object and then back to the receiver is generated by the echo pin...