This Instructable demonstrates a method of increasing the measuring range of the popular HC-SR04 ultrasonic distance sensor.
The enhancement in range is based on reducing the 'field of view' (FOV) of the basic sensor by using it as a feed element for a parabolic dish.
No changes have been made in the electronics of the basic HC-SR04 sensor. However, a blanking circuit has been added externally so as to ignore the first reflection/distance from the feed element to the parabolic dish.
The HC-SR04 is connected to an Arduino uno which displays the measured distance on a standard PC1602 16X2 LCD display. The distance is also sent on the serial link through the USB connector.
For outdoor experiments the system was powered through the USB connector using mobile power bank.
A maximum distance of 9.24 meters was achieved in the experimentation as compared to the 4 meters specified for the basic sensor.
I wish to acknowledge useful inputs from Emil's Project Blog where he has provided an excellent tear-down of the HC-SR04 ultrasonic distance sensor:
The specifications of the HC-SR04 ultrasonic sensor indicate a measuring angle of 15 deg. When used as feed element for a parabolic dish, so that the dish is fully illuminated it needs to be placed at a sufficient distance from the dish. A shallow dish is required so that the focal length matches this requirement.
An old frying pan with a diameter of 250 mm and a depth of 16 mm is chosen as the parabolic dish. Standard calculations for sound in air at 40 kHz indicate a focal length of 24.4 cm and a FOV/ beam width of 2.31 deg.
The reduction in measurement angle/FOV from 15 deg to ~ 2.3 deg will be used to provide the increased measurement range.
The pan handle-arrangement is modified and a aluminum tube suitably bent is taped to the handle bracket to form the feed support beam. The HC-SR04 sensor is fixed along the center line of the parabolic dish at a distance of ~ 24 cm.