LIDAR is an acronym for Light Detection and Ranging. Instead of Radio waves which are generated and reflected off of targets in RADAR, LIDAR uses Light waves for the same purpose. Light has a much higher frequency, and has the potential of generating much more accurate ranging measurements.
The light leaves the laser typically in a series of pulses. A very accurate and exceptionally fast clock is needed to count the time the light takes after it leaves the laser and is reflected back to a sensor. Since light travels at a whopping 299,792,458 meters per second, large scale distances don't require extremely fast clocks to measure. For example, if you had a large reflector on the moon, (about 400,000,000 meters from earth) it would take about 1.3 seconds for light to do the round trip back to your crude LIDAR unit. You might be able to use your stop watch, of course you would need a laser strong enough to get through the earths atmosphere twice and a sensor sensitive enough to pick it up. However, as the distances become smaller your clock will need to be more accurate. To have a LIDAR unit accurate enough to pick up resolution in meters it would be nice to have a clock which could stop on a billionth of a second. Good Luck.
Another form uses interferometry to determine range. Interferometry is the interference of light with itself. Many physics books show a simple experiment of light passing through a small slit. A series of light and dark bands appear on the other side of the slit. It turns out you can generate this interference pattern by splitting a laser then re-combining the beams together. If the distance one of the beams travels, changes, the pattern will change too. <<Michelson and Morley reference>>
My intention for this device would be to provide the distance measurements so a robot could reasonably map its surroundings. So a scale of centimeters would be nice. Since I don't have an extremely accurate clock or an unlimited budget, I created a LIDAR unit which used triangulation in order to produce accurate measurements.
First we are going to need to move the laser in a scan line or some other pattern. This will be necessary in order to derive range distance. In this example we are going to move the laser back and forth in a regular scan line. The motor we will be using is a common (although rare now) 5.25 floppy stepper motor. I just happened to have an old enough computer, which had one of these antique drives.
I removed the drive from the controller circuitry because I was interested in mounting it on a mobile platform (Loki).
Next, you will have to determine which lines will drive the motor. For 5.25 drive steppers, there are usually 5 lines. <<other methods - dc controller - nice thing about stepper is positioning>>
Mount the pen laser on the stepper motor. A little hot glue here (Martha Stewart would be proud).
Aug 16 2008 5:16 am
Thanks AlexM, I appreciate the great support. Best Regards, GroG
Aug 15 2008 11:59 pm
Your blog is interesting! Keep up the good work!