SparkFun Forums

[cheesy]

I'm looking for a relatively cheap laser range finder that could be hacked to hook up to a microcontroller. I have a couple ideas for uses...

I didn't realize how accurate these had become, apparently within a centimeter of accuracy. Wikipedia mentions the Bosch DLE 50 and Stanley Works TLM 100 as being fairly cheap (~$100) but I couldn't find any information interfacing with them.

Thoughts?

[wiml]

Wow, I had no idea they'd gotten so cheap. Are those true time-of-flight rangefinders?

I googled a little but the rangefinders with serial outputs were all in the expected $2k-and-up range.

[NleahciM]

Wow, I had no idea they'd gotten so cheap. Are those true time-of-flight rangefinders?

I googled a little but the rangefinders with serial outputs were all in the expected $2k-and-up range.

I believe most laser rangefinders that you'll find actually look at phase difference in a modulated signal, instead of time of flight. Measuring time of flight for something moving at the speed of light is pretty nasty if you want good resolution.

I've been thinking this summer I might try to build such a device though. Time of flight measurement could be done with one of Acam's TDC chips, such as the TDC-GP2 (http://www.acam.de/index.php?id=105) which has 50ps resolution. The laser pulse could be generated with a laser driver chip that is designed for high speed digital operation. My only hold up is choosing the laser and the receiver. Most photodiodes that I've seen have response times in the microseconds at best, and I think most laser diodes are similar. I'm not entirely sure how to get around such a problem.

[SOI_Sentinel]

Actually, hunting rangefinders are time of flight, but you only get +/- 1m or 2m accuracy out of them. Timing this hardware is possible due to the low resolution.

I'd love to hack into the laser rangefinders (heck, I thought those units were in the $250US+ range), but they get people to pay BIG MONEY to get a computer connection going. It's also rather slow update rate.

One laser rangefinder system(I've done extensive looking around about a year ago) I like is the closed loop phase rangefinder. This one might be easy enough to build yourself. It is patented IIRC. Take a frensel lens and put your laser at the center on the open side. Put your photodetector at the infinity focal point of the lens. Use a circuit to invert the signal from the photodetector to control the power of the laser pointer (detect = laser off, no detect = laser on). What we're setting up here is an oscillator. If you can get a good read on the reflection, the oscillation will be equivalent to twice the distance plus a fixed offset. The problem with this system is that you get really REALLY high frequencies at short ranges. Direct measurement is difficult, yes, but if you use one of the flexible TI clock controls you can divide this down on the fly, arbitrarily to get something readable by a microcontroller.