Thinking... Instead of measuring the time of a reflection returned from an object. What if we had 2 devices synchronized by GPS or an accurate clock. One sending the ping, the other receiving it. If we can measure the delay within 1-2us that would be accurate. Roughly 0.01". Obviously that is not possible because of the physics of a sound wave.
What is the theoretical limit using the frequency of the ultrasonic sensors in this configuration?
It's the same as the normal method.
Let's use 100khz as an example. Each cycle is 10us. So 1/10"? Certainly <1/2". Averaging multiple readings.
Wouldn't this greatly increase the range compared to using only 1 device?
You could send a ping every 2ms once you know the rough distance.
Then you'd have 500 measurements to average in only 1 sec, regardless of the distance.
Obviously the limitation would not be the accuracy of the PPS clock, since GPS is +-10ns.
10ns is about 10ft at the speed of LIGHT!
We'll leave that for another LightPing Library...
How can I use this method with the receiver in a Quadcopter?
The problem is the sound from the motors and blades.
The obvious answer is to put the transmitter in the air,
the receiver on the ground where you want to land, then Xbee to send the data.
This works much better, with a huge increase in range, compared to reflecting from the ground when it's grass.
Thoughts?