HC-SR04 Ultrasonic Sensor Library
This library can be used to read data from the HC-SR04 ultrasonic sensor.
I am in the process of releasing a version 2.0 of this library. The accuracy has been greatly improved. And now has an additional method to connect it to a temperature sensor. I am also toying with the idea of making it work in an interrupt instead of being polled. I would like to get this into the code before version 2.0 is released. Version 2.0 will NOT be downwards compatible with the currently released version.
Features
There are five methods in the Ultrasonic class.
Ultrasonic::CM and Ultrasonic::IN are static const class member objects on the Ultrasonic class.
long timing() This method reads data from the sensor. The return value is used for the microsec argument to the next method described below.
long convert(long microsec, int metric) This method converts the microsecond output of timing() passed to microsec to either centimeters or inches. The metric argument can be either of the two member object discribed in number one above.
void setDivisor(float value, int metric) This method permits the changing of the cm and in divisor so the accuracy of the sensor can be adjusted for distance. The value argument is taken from the table below and the metric argument is either of the two member objects from number one above.
bool sampleCreate(size_t size, ...) This method sets up the buffer(s) needed to derive the standard deviation. The size argument is the number of buffers that you will need. For each buffer, you need to pass an additional argument indicating the length of that buffer. ex. bool success = sampleCreate(3, 10, 15, 8) This indicates that there will be three buffers each with lengths of 10, 15, 8 respectively. You should check the return value for true before proceeding with calling the two following methods.
void sampleClear() This method resets all the buffers to zero.
float unbiasedStdDev(long value, size_t bufNum) This method generates the standard deviation. The value argument can be the return value of either timing() or convert(). The bufNum argument is the ordinal number of the buffer meaning 0 - n. If you have defined three buffers the numbers would be 0, 1, 2.
Divisor Chart
Inches
Distance |
Divisor |
Default |
6.25 |
68.3333 |
|
18.25 |
70.1633 |
|
36.25 |
71.6152 |
|
54.25 |
72.3182 |
|
72.25 |
72.5384 |
|
90.25 |
72.6277 |
|
108.25 |
72.9473 |
|
Centimeters
Distance |
Divisor |
Default |
15.875 |
26.9029 |
|
46.355 |
27.6233 |
|
92.075 |
28.1949 |
|
137.795 |
28.4717 |
|
183.515 |
28.5584 |
|
229.235 |
28.5936 |
|
274.955 |
28.7194 |
|
Notes:
Python Serial Terminal
Also available is a serial terminal specifically written for gathering data for this project. It is a read only terminal and can create CSV files of the incoming data. It could be used with the standard deviation example sketch.
Usage: readSerial.py [h] -d <device> -c <CSV File> -s <Raw data dump file>
Options:
-h, --help show this help message and exit
-d DEVICE, --device=DEVICE
Serial device
-c CSVFILE, --csv=CSVFILE
CSV output filename
-s STREAM, --stream=STREAM
Raw stream filenameThe script can be found below:
Download
NOTE: The latest version supports changing the cm and in divisor. Changing these divisors will make the distance more accurate between different distances from the sensor. The documented divisor 29 for cm and 74 for in seem to work well only at the maximum range of the sensors, 15 feet. Where the current default of 27.6233 for cm and 70.1633 for in work better at the 46/18 cm/in distances.
SVN Repository This is off site and may not be accessible at all times.
Latest Version: 1.1.2
WARNING: If you downloaded any of these packages before 1:00 PM EST on Sep 17, 2011 there was a very big bug in the UltrasonicDemo.pde. Please download the latest package.