Measuring distance between 2 sensors


Say I have 2 robots and i'm interested in measuring the distance between the two of them (minimal detection range as possible and maximal range of at least 3 meters)

What can i use to achive this?

I have looked at ultrasonic sensors but from what I can tell they are only used to measure distance between themselves and solid objects, and i need something that can measure between 2 sensors. (360 degrees)

If this is not possible, then can i use a simpler approach of creating a "link" between 2 sensors, and once that link breaks (say at a distance of 3 meters) then both robots will know it?


This comes up every few months. There are many solutions but no satisfactory ones have been reported.

You can use two ultrasonic range finders where one has the receiver removed and one has the sender removed. You need a radio link to trigger them simultaneously. The one with the receiver can then time how long the sound takes to arrive. Since you have the radio link the receiver side can then tell the sender side the results so they both know.

But it is not 360 degrees is it?

Think thunder and lightning. The receiver starts a clock when is sees the lighting from the sender and stops the clock when it hears the thunder.

Grumpy_Mike: But it is not 360 degrees is it?

It could be if you face the sensor upward and put a conical reflector above it. It may take a more sensitive device than the typical $2 rangefinder but it should be possible to get 360° and 3 meter range. At least the sound doesn't have to travel round-trip and rely on the quality of a reflecting surface.

Thanks for the suggestion.

I'll be sure to test that out.