DPRG mailing list archives: [DPRG]Wall-E -> 1GHZ computers laser rangefinding

Thu Jul 10 16:33:13 CDT 2008

Hello guys, I have another question.  Since I'm changing the photodiode I'm
using o a very fast response one, I will need to use a 650nm laser/detector.
But the 850nm one only outputs 4.23mW of light and the one I was planning to
use originally outputs 5mW of light.  Will that affect my range?  Also, I
need some help in building the receiver which means using op-amps (I'm not
very experienced in that area), or could I use a pre-amplifier then use a AD
converter?  

______________
Ray Xu
rayxu at tx.rr.com

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
Of John Swindle
Sent: Wednesday, July 09, 2008 9:46 PM
To: dprglist at dprg.org
Subject: Re: [DPRG]Wall-E -> 1GHZ computers laser rangefinding

Folks:

I think we all like the idea of direct time-of-flight measurement 
of light because it seems so straightforward and cool, but as you 
probably already know, the laser rangefinders do it with the 
phase of the light, not the flight time. Indeed, it can be done 
with cheap parts at about 25MHz, not 1GHz. When I was playing 
around with rangefinder ideas, I found the plans for the circuit, 
but I discarded the link. It didn't take much searching.

When I was in college, I thought I could directly measure the 
speed of light using a strobe, a photodetector, and a fast 
digitizing oscilloscope. It is considerably harder than it would 
seem. I only got a C on that project. Ouch!

Back to my passive sonar stuff now.

John Swindle

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