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I'm looking for a simple way to measure the distance between 2 devices, basically 1 device will be placed in each leg and one of them will measure the leg stride, at any moment, by calculating the distance between both mechanisms. I've read you could measure distance with an ultrasound sensor and an ultrasound transmitter or a magnetic sensor, but are they accurate between 0 and 1 meters, in any direction?
If such a solution is feasible could someone point me to some documentation or a project already made?

The specs are roughly the follow:

  • distance: 0 to 1m
  • accuracy: about +/-5cm
  • type of range: omnidirectional (or at least with a good angle)
  • size: small enough to fit on someone's heel
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  • \$\begingroup\$ Any distance sensor is highly directional, so I'm not sure what you mean by "in any direction." \$\endgroup\$ – coder543 Dec 14 '14 at 3:05
  • \$\begingroup\$ Ultrasound will probably work, if this is kind of a lab project or science project type of thing. If it has to be super reliable, it is going to be kind of challenging. \$\endgroup\$ – mkeith Dec 14 '14 at 5:56
  • \$\begingroup\$ If you know what accuracy you need, why not include it as part of your question? For that matter, why not include as much information as you can about what you want to do and help to cut down on all this useless chatter? \$\endgroup\$ – EM Fields Dec 14 '14 at 8:51
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Laser rulers are widely available at hardware stores.

http://www.homedepot.com/p/Bosch-50-ft-Compact-Laser-Measure-GLM-15/205387213

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It is only an idea, because I do not know if such device exists commercially. I think an elastic band connecting the two legs, and on the band, a load cell. The deformation of the cell can be associated with the deformation of the band, and tape deformation, the separation between the legs, in either direction.

Of course, the deformation of the elastic band should meet a fairly linear relationship with the separation of the legs, at least within the range of application.

Personally, I have used a similar method for measuring respiratory rate. On an elastic band that encircles the patient's chest, I placed a permanent magnet and a Hall effect sensor. The variation of the magnetic flux gives me chest deflection relationship with each respiratory cycle.

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