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DPRG: Re: Ranging data with Sharp module

Subject: DPRG: Re: Ranging data with Sharp module
From: Gary Croll gary.croll at ucr.edu
Date: Tue Sep 21 03:06:22 CDT 1999

Robert, thanks for the renewed interest in the project. I have not done
much with it since this post, except, to determine that the Sony IR modules
are NOT the same as the Sharps. This could account for the unusually good
results I received. One difference I noted is DON'T USE A PULLUP ON THE
OUTPUT. It ruines the module, why, I don't know. I've also replaced the
2N2222 transistor with a power MOSFET and lowered the value of the limiting
resistor.

I do want to get back to it soon. A member of our Yahoo club works for an
LED manufacturer and sent me some samples to play with. They are super high
output with very narrow beamwidths that should make the project even more
robust. 

Your letter might just be the kick in the pants I need to get back in the
shop and finish this thing. Heck, the yard work can wait!


At 06:49 PM 09/20/1999 -0500, you wrote:
>Gary,
>Did you ever get this project working reasonably well? Did you publish it
on your
>website?
>Care to share it or sell me a newsletter subscription so I can use it hear
at the
>DPRG?
>I'd like to build it into a PCB for beginner robot builders.
>What do you think?
>Regards
>Robert Jordan
>DPRG Sec 1999
>
>Gary Croll wrote:
>
>> Scott,
>>       I don't have the final design worked out yet. It is still partially
>> prototyped on my bench.
>>
>> The transmitter consists of a generic 555 oscillator circuit running at
>> 40Khz with a 50/50 duty cycle. I'm using 40Khz because that is the center
>> frequency of the particular IR receiver module I'm using. The output of the
>> 555 feeds a 2N2222 transistor through a 1K resistor. Ground the emitter and
>> put a Radio Shack high output IR led in the collector circuit. Use a 150
>> ohm resistor for current limiting to the 5 volt source. Pin 5 of the first
>> 555 gets modulated by a second 555 running at 500 hz with a 50/50 duty
cycle.
>>
>> The receiver consists of a generic IR receiver module like the one at Radio
>> Shack. The ones I'm using happen to be Sonys but only because I got a lot
>> of them at a very good price. The output from the module is a demodulated
>> signal consisting of a variable pulse width based on distance to target.
>>
>> At zero range, the pulse width is 50% and decreases to 1% at maximum range.
>> You can use this data in several ways and this is the part I am fine
tuning.
>>
>> A cheap and dirty way to go if you only need relative distance is to use a
>> small capacitor to integrate the pulse into an average DC voltage who's
>> amplitude is based on pulse width. For example, at zero range,(50%), the DC
>> level might be 2.5VDC. At maximum range, the voltage might be a few tenths
>> of a volt. This could be measured by several comparitors set for a min/max
>> distance
>> window.
>>
>> Another way to go would be to use the pulse to enable an oscillator. Then
>> you could count the pulses. Choosing the correct frequency and inverting
>> the result could give you a direct distance measurment.
>>
>> In my tests so far, reliable range was about 4 feet for fairly flat
>> surfaces. I was able to detect my hand reliably at 3 1/2 feet. In a typical
>> maze or wall following scenerio you are only concerned with a couple feet
>> at most and this should work very well.
Gary Croll (KE6GHS)
University of Ca.
B-221 Sproul Hall
voice (909) 787-3041
fax (909) 787-7282
video (909) 787-8813

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