Better library: NewPing
The example below is a simple implementation that is easy to understand and great for simple testing. However, it is slow, is not meant to be run from interrupt code, and does not bound the pulseIn call by adding ", 38000" or whatever the appropriate maximum timeout (in microseconds) is for your sensor. In other words this code can introduce up to a 1 second delay as the worst case timeout to pulseIn.
If you need more efficient code that can be run from interrupts and can be used to talk to multiple sensors at the same time, look at NewPing from http://code.google.com/p/arduino-new-ping/
Simple example to play with
// * Copyleft 2007 Jason Ch
This code returns the distance in Inches...
I think it's more accurate than other code I have seen online and returns more usable results. Remove the *.39 to return cm instead of inches.
You could make float ultrasoundValue = 0; but then you can't print it unless you transfer it into another type, but it could be used for further calculations.
unsigned long echo = 0;
int ultraSoundSignal = 9; // Ultrasound signal pin
unsigned long ultrasoundValue = 0;
unsigned long ping()
pinMode(ultraSoundSignal, OUTPUT); // Switch signalpin to output
digitalWrite(ultraSoundSignal, LOW); // Send low pulse
delayMicroseconds(2); // Wait for 2 microseconds
digitalWrite(ultraSoundSignal, HIGH); // Send high pulse
delayMicroseconds(5); // Wait for 5 microseconds
digitalWrite(ultraSoundSignal, LOW); // Holdoff
pinMode(ultraSoundSignal, INPUT); // Switch signalpin to input
digitalWrite(ultraSoundSignal, HIGH); // Turn on pullup resistor
// please note that pulseIn has a 1sec timeout, which may
// not be desirable. Depending on your sensor specs, you
// can likely bound the time like this -- marcmerlin
// echo = pulseIn(ultraSoundSignal, HIGH, 38000)
echo = pulseIn(ultraSoundSignal, HIGH); //Listen for echo
ultrasoundValue = (echo / 58.138) * .39; //convert to CM then to inches
int x = 0;
x = ping();
delay(250); //delay 1/4 seconds.