Details of the Laser Range finder

So, i would guess that at least 20 individuals asked me how to make a laser range finder at the 2003 fire fighting contest. By Sunday i was getting pretty tired of answering the same question so i decided to make this web site. Since in my college it seems that every single project is done in groups i have become used to sharing just about everything i come up with, so you are in luck. I hope that whoever reads this overview will be inspired to make their own system for a fire fighting robot to advance the contest.

Parts

The following are the parts that i used to make the ranger. Substitutions are always possible.

• LIS-1024 Linear image sensor by Photon Vision Systems

• Green Laser Diode Module

• A lens assembly from miniature camera

• TLC0820 parallel 8 bit flash Analog to Digital converter

• 4047 oscillator, 74HCT00 quad NAND gate.. other little stuff.

The basic principle of this ranger is to measure distance through triangulation. A laser is used to illuminate the object you would like to measure to and a linear image sensor or other sensor is used to measure the angle to the spot. The laser and image sensor are mounted at a known distance apart pointed in the same direction.

Because the average hobbyist doesn't have access to a wide variety of lenses, lasers or image sensors, many calculations are irrelevant because you couldn't get parts to fit what you calculate. The parts that i used were what i could get but some things should still be kept in mind if a choice exists.

The more resolution your image sensor has the better the accuracy. The image sensor i have has 1024 pixels and provides decent resolution and accuracy. If you were to use something easy like a cheap camera that may have only 300 pixels in a line your resolution will be severely effected. More is better but be careful of the price. I am not very much into optics and i pretty much experimented with the lens to get it to work. I know it has to be about as wide as the active area of your sensor and with a focal length of about 1cm. Other than that you can just mess with the sensors position under the lens and the focus until you get something that works.

The microcontoller i used to drive the sensor had internal analog to digital converters but i chose to use an external IC. It seemed that the fastest i could configure the integrated ADC to run, it would take about 75 microseconds per sample, at low resolution. The TI part can make a conversion in about 5 microseconds allowing for at least 100 complete distance measurements per second.

I chose a green laser for 3 reasons. The trinity gym is very red, leaving the possibility open to put a filter on the sensor. Its really bright so the ranger can see pretty far without strange amplification. Its really cool. You could probably use cheaper red lasers just fine. You may have to amplify the video signal though if not enough light is reflected. In fact i would probably try amplifying the signal instead of using a green laser again, it is way too bright to use regularly.

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