Easiest way is to run one ultrasonic at at a time. Fire one, wait for a pre-defined timeout, then fire the other. Your timeout should be based on the maximum range of your ultrasonic sensors.
Another technique that can be used in combination with the above is to mount the sensors at 45 degrees, so that they cross-fire. This lets you detect objects in front or to the side, but reduces the amount of echo one sensor will see from the other.
Thank you for your reply sir Andrew. the first technique is wonderful, i.e. triggering by means of differ in time.
But in my project, i need exact solution.
my project is
That's an ambitious project. Anything related to safety, and dealing with automobiles that travel very quickly is serious business.
I'm afraid I cannot provide you with an 'exact solution'. If you are not ready to tackle a project of this magnitude, you might want to start with something simpler and build up the skills you need over time.
Can you use two different (non-harmonic) frequencies with a notch filter front end for each receiver? Just a thought. The reflected wave frequency sould be the same as the transmitted frequency for each transmitter/receiver pair, correct?
I have to agree with Andrew, this project is ambitious, but if you want to get your hands dirty, might try to look at infrared proximity sensors, at least IR has a bit further reach than PING sonars, and previous experience says that most likely less interference at relatively high speeds as well. as added bonus you can try polarizing source and detector and use 2 or even more sensors at the same time.
I must be missing something; why can't each transceiver use a different band? I remember a (Popular Mechanics?) project from the '60s that put a number of ultrasonic emitter/detector pairs on a rear bumper, and used the returning signal to set the brightness of a line of light bulbs on the dash. It was meant for parking, but the idea is the same.
Theoretically, that is true.
Practically speaking there are inexpensive and easily available ultrasonic modules from companies like Devantech and Maxbotics. Here's a selection available at RobotShop.com.
RadioShack and other places also carry the Parallax Ping sensor, which is another common example.
Or search for ultrasonic HC-SR04, and you will find super cheap knock-offs available on eBay.
I assumed KK would be working with something like one of the above, which would limit him to the same frequency and modulation for both sensors.
Thank you every one for quick response.
Another way to accomplish this is to send out signed pulses that are unique to each transmitter. In a way this is the same problem as how to differentiate between GPS satellites. Each ping is coded and then each receiver listens for its assigned signature. In the case of collision wait random and resend.
Mitre Corp had a similar reflection problem with there Over The Horizon radar. Not sure how or if they solve it 100%.
Wow, I just shut down due to the storm but came back to add. I could be in left field here. But Mitre was using heat and there reflection was like a picture of trees reflected off of water. In fact it was my photo used as a example to that reflection. There the reflected image was 180 inverted. Not sure that helps but if it does you can have it. Me'e