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Distance Sensors

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vne147

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Hey everyone. I posted this question in the robotics forum but didn't get too much activity on it. I'm hoping that here I might get more visibilty and ultimatley, help. So here's the deal.

What I'm trying to do:

I’m working on a project where I need to measure distance with an accuracy of ± 1mm (~ .04") at the most. Better accuracy is obviously preferred if possible. The distances I will be measuring will be in the range 150mm - 750mm (~ 6" - 30").

Solutions considered:

I have worked with several of the Sharp IR distance sensors before but I recently learned that they have a built in 8bit DAC that provides the analog output. Unfortunately, 8 bit resolution would not provide the accuracy I require.

I have also thought about laser range finders but I'm on a budget and not sure I'm skilled enough to pull it off. I did find this old thread. There is an interesting idea in post #14 that I'd like to get people's thoughts on and maybe some help implementing.

There are also of course ultrasonic sensors. I haven't used one before and after doing some searching on the web, I didn't have much luck finding any pre-made ultrasonic sensors with greater that ±1cm accuracy.

I think a sensor that might work is the PING from Parallax. The data sheet says that it outputs a pulse of duration equal to the round trip travel time of the distance being measured. I could easily feed that into a PIC and measure the duration of the pulse. If I clock the PIC at 20 MHz and I can measure the pulse with and accuracy of ± 2 - 3 µs, that would give me the accuracy I need.

My questions:

  1. Does anyone have experience using a distance sensor to obtain this level of accuracy?
  2. Is there anything inherent in the design of the PING sensor that would limit the accuracy I could obtain?
  3. Does my idea seem feasible?
  4. If you were doing the project, how would you do it?

I hope my ideas and questions are clear. As always many thanks for the help.
 
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