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I was asked to build a circuit that will measure the distance travelled of a small vehicle, like a lawn mower.

There's a requirement that it would measure distance travelled in cm/sec. GPS is too inaccurate, and the starting point is unknown. I'm unable to put anything in the ground.

Any ideas? I can use whatever IC I want. I thought of using a camera pointing down, like a mouse, but it seems too complicated to process outside of home.

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    \$\begingroup\$ If it has wheels that make reliable contact with the ground a quadrature encoder would work, is that the case so you really just need to measure how far the wheels rotate? \$\endgroup\$ – PeterJ Jul 18 '15 at 14:43
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    \$\begingroup\$ A lot of companies would like to come up with the answer to that question. \$\endgroup\$ – Chu Jul 18 '15 at 15:00
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    \$\begingroup\$ I suggest that you review Dead reckoning. The use of accelerometer (speed measurement), and magnetometers (direction) might mostly do the job for you. Looks like your system has a wheel. So a wheel speed sensor can also assisting acquiring additional infomation make your system accurate. Also look at irobot The hardware to the most part is open source. This should help you with some ideas \$\endgroup\$ – Mahendra Gunawardena Jul 18 '15 at 16:02
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    \$\begingroup\$ "measure distance travelled in cm/sec"?? distance can be in cm, cm/sec is speed, not distance. Try to be more precise in the formulation fo your question. \$\endgroup\$ – Wouter van Ooijen Jul 18 '15 at 17:19
  • \$\begingroup\$ Have a look at the DARPA vehicle challenge; some entries successfully used the "optical mouse" technique. \$\endgroup\$ – pjc50 Jul 18 '15 at 19:26
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Since the small vehicle is like a lawn mower I am assuming the small vehicle has wheels. You have many options to choose from based on your requirements.

  • As PeterJ suggested you can use a quadrature encoder.
  • Another option is use and Hall effect sensor. This type of application is used frequently in automotive applications.
  • The use of an accelerometer will enable speed measurements. Consider a three axis accelerometer, thus this will infomation as as to if the vehicle going up an incline or down an incline. I create a simple accelerometer demo using Beaglebone black, Embedded QT and ADXL345 which can be found here. The source is available to public on github. I also did similar demo using TIVA ARM Cortex M4 + ADXL345. I can make the source code pubic if interested.
  • The use of a magnetometers will help determine direction in XY direction

Also take a look at the Dead reckoning concept. Dead reckoning doesn't use GPS, and is widely used in automotive navigation applications when GPS is not present, such as driving through a tunnel.

Another interesting application is irobot create. As I understand the both hardware and software is open sourced. This will give some good ideas for your project. Below is picture of guts of iRobot command module.

enter image description here

Another option would to use myRio from NI. Although the hardware is not open source myRio allows you the connect to LabView to help develop algorithms.

References:

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