Subject:
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Re: IR concept
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 30 Mar 1997 10:55:35 GMT
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Original-From:
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Adam <adam@STOPSPAMring.zenox.com>
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Viewed:
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3994 times
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Chuck,
If you have the scematics for the IR sensor that uses the 555 and opamp,
Iw oudl be interested in looking them over. I understand your theory, but
the scematics would save me some time in ironing out the nitty gritty stuff.
Thanks.
On Fri, 28 Mar 1997, Chuck McManis wrote:
> Adam wrote:
> > An alternate IR system....
>
> [Digitize the output from an IR LED with and without
> a signal present to achieve some common mode noise
> rejection.]
>
> This type of system is susceptible to being 'blinded' by
> high intensity IR sources (try it outside :-) I used a
> similar technique on a Sumo robot to detect the white
> rim of the Arena, only the real contest was held under a
> skylight and I discovered this weakness the hard way :-)
>
> > I've been scanning through some of the IR stuff to see if
> > I can't pick out a good solid system for collision avoidance
> > on a short range (approx. 6-10cm) scale, but everything seems
> > like alot of trouble.
>
> If you're maximum detection range is 10 cm, (< 4 inches) then I
> strongly recommend that you consider a high compliance whisker.
> Put a piece of #80 piano wire (spring steel wire) with a ball
> on the end (a glob of hot glue works well) and mount it in a
> deflection detection chamber (ie a piece of brass tubing.)
>
> Write if you want manufacturing details (the hot glue gun is
> your friend :-)
>
> > I'm curious to know what others have to say about this approach.
>
> As in all sensor designs it has its strong points and its weak
> points. Easily implemented in hardware, susceptible to some common
> interference sources.
>
> Another common way to implement this sensor is to hook the LED
> up to a modulating source (such as a square wave from a 555),
> then feed that input, and the output of a detector into an
> opamp. Since one input is inverting, and the other non-inverting,
> if you have the same signal on both pins (the detector is following
> the transmitter) the opamp will produce zero output, when the
> signal on the detector fades, the output of the opamp will increase.
> You can rectify the output and put it through a level detector to
> get a binary output. This sensor gets even more interesting if you
> put a variable feedback stage into the opamp so that the gain of
> the detector input is programmatically controlled. If you can
> recover the signal by increasing the gain then the input to the
> gain control gives you a rough approximation of the distance to the
> target (remember that light intensity is 1/d^2 so the output curve is
> exponential!) At that point you've pretty much built one of the
> Hammatsu sensors by hand. You can increase selectivity by putting
> a bandpass filter on the output of the IR detector.
>
> The bottom line on sensors is that if you can get three different
> kinds of sensors that can all detect the same thing, then you
> have a very reliable way of detecting it. So the more the merrier.
>
> --Chuck
> --
> cmcmanis@netcom.com http://www.professionals.com/~cmcmanis
> All opinions in the non-included text above are the sole opinions of
> the author.
>
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Message is in Reply To:
 | | Re: IR concept
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| (...) [Digitize the output from an IR LED with and without a signal present to achieve some common mode noise rejection.] This type of system is susceptible to being 'blinded' by high intensity IR sources (try it outside :-) I used a similar (...) (30 years ago, 29-Mar-97, to lugnet.robotics.handyboard)
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