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Just a follow up to this topic now that I have an RCX of my own (thanks
Santa...and my wife)
I found that using the Radio Shack light sensors for detecting on coming
trains to the crossing works great. No special wiring needed at all, I
basicly unhooked the sensors from my existing Crestron control system and
added a LEGO wire connector and then plugged it to the RCX. By monitoring
the levels from the sensor I'm able to get a very acturate response from the
trains passing over the sensor. Actually since I can control the threshold
of the sentivity of the sensor it works better than with my old system.
I will post some more detailed pictures of my sensor soon. Basicly it's a
Radio Shack sensor mounted in the middle hole of a 2x4 technic plate facing
up. I snap this between the track before and one after the crossing. The
logic of the code is if either sensor is covered lower the crossing arms (if
they already aren't). Once both sensors are no longer covered for more than
4 seconds then raise the arms. The 4 second wait eliminates the problem with
sensing the graps between the passing train cars.
Of course after I figure this all out I find that Michael Gasperi already
covers using the this type of sensor on his web site at:
http://www.plazaearth.com/usr/gasperi/cds.htm
jt
-------
James J. Trobaugh
North Georgia LEGO Train Club
http://www.ngltc.org
In lugnet.trains, James Trobaugh writes:
> At this point I don't have the sensor hooked to an RCX due to the fact that
> Santa hasn't brought me one yet (hint hint Santa). I currently have the
> sensor hooked into a Crestron Control system (http://www.crestron.com). The
> sensor is hooked to a digital I/O port that monitors either a open or closed
> event on the sensor. From what I've been able to find out, this would also
> work for an RCX. After this December I will be trying this out and find out
> for a fact if I am correct.
>
> jt
>
> In lugnet.trains, Steven Barile writes:
> > James,
> > Are they directly wired to the RCX or is there a resister in series. BTW
> > where is the web page on the electrical specs of the RCX and home brew
> > sensors? I can't remember.
> > SteveB
> >
> > In lugnet.trains, James Trobaugh writes:
> > > Chris,
> > >
> > > Another great little sensor for train detection, via Radio Shack, is the
> > > little photo sensors they sell. I put them inside of a 2x4 technic plate and
> > > then snap them face up on the track. This way they use the omni light from
> > > the room as the light source, when the train crosses over the sensor the
> > > light source is removed and the train's arrival is detected. By placing one
> > > on both sides of the crossing you can tell if the train is still in the area
> > > of the crossing. The basic logic is if either sensor is triggered lower the
> > > gates, once both sensors are clear raise the arms back up.
> > >
> > > The only problem I had with this was at some of the shows I've done they
> > > don't turn on the main lights till the show starts (i'm sure to save money),
> > > and sometimes the sensors wouldn't work till the lights were all turned on.
> > > Not a big deal, just that I couldn't test the sensors till show time. I did
> > > start carrying a flash light for testing reasons though.
> > >
> > > Here are a few pictures of the sensors I've built:
> > >
> > > http://www.ngltc.org/novgats/image50.htm
> > > http://www.brickshelf.com/cgi-bin/gallery.cgi?i=20391
> > >
> > >
> > > In lugnet.trains, Chris Phillips writes:
> > > > As has already been reported by others, I built an automated railroad
> > > > crossing for the NELUG train display at last weekend's Greenberg show. I
> > > > wanted to take a moment to describe the "homebrew" sensor that I used to
> > > > detect an approaching train so that others might benefit in their own layouts.
> > > >
> > > > I originally tried several techniques to detect the presence of a train,
> > > > including the touch sensor, the light sensor opposite a light source, and
> > > > the good old infrared "radar" technique that has been well-documented on the
> > > > robotics forum in the past. I also considered using Vision Command, but I
> > > > didn't want to have a PC in the loop if I could avoid it. None of these
> > > > techniques was very reliable: I couldn't find a good way to trip a touch
> > > > sensor without derailing the train, and the other techniques required a lot
> > > > of highly visible and unsightly "plumbing" somewhere along the track. I had
> > > > pretty much abandoned the idea of using an RCX to detect a train before I
> > > > remembered an idea that I had awhile back but never tried, due to my
> > > > semi-irrational aversion to non-LEGO solutions.
> > > >
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