Detecting Horizontal Movement

[Atom058]

Hello - I have an application where I wish to detect my movement over ground (asphalt, dirt, grass, snow, etc.). I need non-contact measurement from about 3 feet off the ground. I am not concerned with speed or distance, just the fact that I am moving. I thought of an accelerometer, but I need it to continuously output a signal the entire time I am moving and stop when I stop - similar to what an optical mouse does when you move it over a surface. I've thought of using ultrasonic sensors or even PIRs, but I don't think they will give me the results I want. Possibly a laser pointer aimed at the ground, but what would I use to sense the scattering when I move? I don't think a vibration sensor would work as there are too many things that could trigger it falsely. Anyone have any suggestions? Thanks!

[Darrel Taylor]

You can do that with a simple accelerometer.

By "integrating" the signal, it can tell you when it's moving.
Integration is just a subtraction of a "Base" reading from the accel. reading, and adding the difference to an accumulator variable.

Compensation for "Drift" is also needed, but can just be a new "Base" reading when the object is not moving.

[Atom058]

Darrel - Thanks for your response, but don't accelerometers just detect changes in speed? I would think that once speed was constant, there would be no signal until the speed changed again (sped up or slowed down). Jeff

[rsocor01]

Darrel - Thanks for your response, but don't accelerometers just detect changes in speed? I would think that once speed was constant, there would be no signal until the speed changed again (sped up or slowed down). Jeff

Yes, you are right. The acceleration of any object is defined as dv/dt, which is a change in velocity divided by a given amount of time. If the velocity doesn't change then the acceleration is zero. However, if you want to detect your own movement, running or walking, chances are that you won't be able to maintain a constant speed. There would be small fluctuations in your body speed that the accelerometer would be able to detect.

Robert

[Ioannis]

May be a gps module can help if the speed is over its lower detecting limit.

Ioannis

[mackrackit]

Add a compass and you have everything a "smartphone " has. They work very well for tracking movement.