Subject:
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Re: flame sensor
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 23 Dec 2002 00:34:07 GMT
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Original-From:
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Steve Baker <sjbaker1@NOMORESPAMairmail.net>
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Viewed:
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809 times
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Vincent Grace wrote:
> I am trying to build a sensor to attach to the RCX that can sense a candle
> flame. I'll be attaching it to a robot that will use it to look for a
> candle, go to it and extinguish it.
> If any one has heard of such a sensor that's able to be interfaced with the
> RCX I'd be grateful if they could e-mail me about it.
Lego actually make an 'official' temperature sensor. I guess that in
combination with the light sensor, you'd be able to detect a candle flame.
The biggest problem may be how to get the temp sensor close enough to the
flame to unambiguously know it's a nearby candle flame and not (say) the
sun. If you get too close, you'll melt the plastic - but the temperature
of the air more than a few inches away from the flame isn't much higher
than ambient. Ideally, you'd want to place the detector above the flame
and gradually lower it until either you detect a nice high temperature or
you have lowered it far enough to block the light from the light sensor.
Be prepared to retract the sensor quickly if the temperature gets dangerously
high.
But how do you know that you are close enough? I guess you could use
two light sensors - one pointing forwards and the other angled inwards
to produce a crude stereo image. If the robot located the light source
using the forward pointing sensor - then drove towards it until the other
light sensor also produced a bright output, then you'd have a good idea
where the light was. If you held the temp sensor on a long boom hanging
over the place where the line-of-sight of the two light sensors intersected
then at that point, you could just lower the temp sensor at that location
and get a temperature reading.
Presuming (Light+Heat == Candle Flame) - this would do the job.
You could probably use some of the Lego pneumatic components to make
a water gun. One blue pneumatic tank filled with water should be
plenty to put out a candle.
Unfortunately, you probably need more than one RCX to do this, aside from
the three sensors (two light, one heat), you'd need one motor to drive with,
one to steer with, one to lower the heat sensor and one to actuate the
pneumatic pump to squirt water. That's four motor outputs - and you only
have three. You'd probably be able to figure out some mechanical way to get
around that. eg: Driving the third motor with the steering hard to the left
lowers the boom and driving the third motor with the steering hard to the
right could squirt water. Since you don't need to drive *and* squirt or
lower the sensor - this could work.
So, I think this is a challenging problem - but not impossible, even with
standard Lego parts.
> I think it could sense the ultra-voilet or infra-red light coming off the
> flame.
The standard light sensor is quite sensitive to infra-red light, which a candle
flame produces in abundance. I doubt that a candle produces much UV
light - which is just as well because there is no way to detect it using
Lego parts.
> It would have to be very responsive and fast at reacting. Also, it
> would only have to be able to see the flame from a foot away max.
How easily you could do that with the light sensor depends crucially on
the amount of other light in the room. If the room is in bright daylight
with the sun visible through one or more windows, I think this would be
almost impossible. If it's a completely dark room, I think detecting a
candle at a foot would be really easy. Somewhere between those extremes
will be your test environment.
When you say "fast at reacting" - how fast is fast? Ten seconds? One second?
How sensitive are you to 'false positives' - how bad would it be to squirt
water at the Sun (say) by accident?
> Once again
> if anyone has heard of something that could do this, I'd be grateful if they
> could contact me ASAP.
The only thing I can recall that even used the heat sensor was the
boiling milk detector in the Ferrari brothers book...I don't think
thats very relevent to your problem though.
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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 | | flame sensor
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| I am trying to build a sensor to attach to the RCX that can sense a candle flame. I'll be attaching it to a robot that will use it to look for a candle, go to it and extinguish it. If any one has heard of such a sensor that's able to be interfaced (...) (22 years ago, 22-Dec-02, to lugnet.robotics)
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