Basically, I want to detect an ultrasonic beacon in a radius around the robot. The beacon would have a separate ultrasonic emitter while the robot would have the spinning receiver.

Are there any existing ultrasonic sensors that would meet this use case or am I stuck hacking one together myself?

Is ultrasonic even the best choice? I was hoping that the beacon would be kept in a pocket, so I figured optical sensors were out.

Edit: The beacon and robot will both be mobile so fixed base stations are not an option.

  • $\begingroup$ Do you need to measure the distance to the beacon, or simply detect the heading? $\endgroup$ Dec 1, 2013 at 13:34
  • $\begingroup$ Yes distance and top-down relative location are what I am trying to get from this. I also added that both the beacon and the robot will be mobile so, fixed base stations are not an option. $\endgroup$
    – cmgriffing
    Dec 1, 2013 at 21:31
  • $\begingroup$ Another option would be a 2.4GHz transmitter, and a little Yaggi antenna on the robot. $\endgroup$ Dec 2, 2013 at 10:29

2 Answers 2


If you were to place 3 ultrasonic microphones/sensors in a triangle layout you should be able to determine the direction of the beacon based on the time difference the ping arrives at each sensor with some straightforward trigonometry. They'd all have to be facing in the same direction (probably upwards) and you may have to find some way to make them omnidirectional. The further apart you can space the sensors, the more accurate the calculation will be.

  • $\begingroup$ Here's a 3D model for an omnidirectionalizer (hehe): thingiverse.com/thing:29775 $\endgroup$ Dec 3, 2013 at 1:28
  • $\begingroup$ That receiver antenna you linked is great. Longshot question but do you know of an omnidirectional ultrasonic transmitter sensor/antenna? If I had more rep I would upvote this answer, but I don't know if it is the answer yet. $\endgroup$
    – cmgriffing
    Dec 4, 2013 at 11:19
  • $\begingroup$ I don't know of any, but that's the point of the antenna I think. I saw some in my googling but I think they were for talking to dolphins or something. They cost a lot of money. $\endgroup$ Dec 6, 2013 at 22:23
  • $\begingroup$ In an open-air environment there would be no guarantee that a directional transmitter would find an omnidirectional receiver. In an enclosed area the bounce would probably be effective enough, though the travel distance of the signal would no longer be accurate and you would have to rely on some type of signal encoding. $\endgroup$
    – cmgriffing
    Dec 7, 2013 at 0:48
  • $\begingroup$ I'm beginning to think that RF will be more suitable for my use-case. Even then, I think a receiver that scans in a circle (like sonar screens) would be most effective. My initial plan was to rig a directional sensor to a slow-spinning(slow as in 100-400 rpm) motor. Maybe even as fast as 800rpm if possible. The faster the better for scanning fidelity. Now I'm thinking it could be a series of sensors/antennae setup cylindrically and polled at the needed rate. I still don't know the proper keywords to search for something like that, does either version exist or am I stuck hacking it together? $\endgroup$
    – cmgriffing
    Dec 7, 2013 at 0:59

I'm not going to mark this as the answer unless others agree it is the answer, but I found an omnidriectional ultrasonic transmitter/receiver: http://www.metrolog.net/ultra40k.php?lang=en

I haven't used it or tested it yet, but it seems promising.

  • $\begingroup$ The link is dead. $\endgroup$
    – Mehdi
    Nov 19, 2015 at 16:01
  • $\begingroup$ I just updated the comment with the new address since the supplier updated their website and url structure. Thanks for letting me know the link was dead so that I could update it. $\endgroup$
    – cmgriffing
    Jun 17, 2016 at 16:33
  • $\begingroup$ The link has died again :'( $\endgroup$ Jun 27, 2018 at 20:43

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