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

Thu Jul 10 19:30:30 CDT 2008

Ray,

The difference between 4.23 mW and 5 mW will only make a very small difference 
in the range.  Having a properly matched emitter and detector pair will make a 
big improvement in the performance of the circuit.

An analog-to-digital converter would be much, much too slow to give any sort of 
meaningful result in this application.  You will need to build a very fast 
amplifier that introduces a minimum of delay into the detector circuit.

Thanks,

Dale Wheat

(972) 486-1317
(877) DALE WHEAT
http://dalewheat.com

ray xu wrote:
> 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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