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laser distance module - 40meter (120')


I am looking for a low cost module to detect fill levels in silos. Red lasers seems to be the best/cheapest solution. (You can buy red laser distance meters at 50 - 100,-USD).

I need a good module for this ... anybody knows where to get it?

Thank You

Peer Hansen


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Comment by Joe Watson on December 6, 2013 at 3:23pm

Although I am sure a laser measuring system could probably work for you, I thought I would pass along a little story about something I did about 30 years ago that seems related.

I was preparing to dramatically increase the load on a water well on my property. The well was drilled more than 120 feet deep. I had no idea what the water level was in the well when there was no demand for water and I had no idea how much the water level would be pulled down when the water in the well was being pumped out at a rate of 18 gallons per minute for extended periods of time. I needed both values.

I did not want to pay a professional service to come perform this test so I determined my own way to measure the distance from the top of the well down to the water. Whenever I removed the cap on the top of the well, I was struck by the time delay in the echo of my own voice down the well. I made a cap with a speaker and a microphone in it. I added a circuit to make a short beep about once per second and drove that into the speaker. In my case, I simply used an oscilloscope to observe the delay time for the beep to travel down to the water and then return to the microphone at the top. Knowing the speed of sound in air (about 1100 feet per second) allowed me to translate the time delay to distance. Of course, now they sell very inexpensive ultrasonic devices to perform this very task although the distance that they typically reach might not be sufficient for your needs. Still, if you are a creative experimenter, I suspect this approach could be made to work for you by adding some appropriate audio frequency filters, amplification, and interface electronics.

Comment by Geoffrey L. Barrows on December 10, 2013 at 1:06am

The ultrasound device method might work, but we've found that they tend to work best against a flat surface perpendicular to the sound direction of travel. The water well is a perfect example (I remember clapping my hand above wells in medieval villages when I lived in Germany as a kid). But the grain in the silo might not work as well.

There should be plenty of options for laser modules on the internet. (I cannot recall what I used but it was pretty generic.) I'd start with a basic laser pointer, see what type of range that can get, and then use the square law. e.g. if 5mW gets you 10m, then you need 20mW (four times as much) for 20m.


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