There are highly reliable switches used to control crossing gates. Why not use that which already exists? Getting the signal from the sensing point to the application point is then a trivial exercise. On Thu, Jul 18, 2013 at 6:34 AM, Isaac Marino Bavaresco < isaacbavaresco@yahoo.com.br> wrote: > A moving train shall induce some voltage across the two tracks as it > crosses the Earth's magnetic field lines. > Perhaps you can detect that IF the tracks are not shorted together at > some point between the train and the detector AND if the signal is > strong enough AND it is not buried in noise, etc., etc > > > Isaac > > > Em 18/07/2013 08:16, Ravi escreveu: > > Russell, > > > > If I had to write the whole story covering all the points mentioned by > > you, then I would not know how many would have had the patience to go > > through the story :-D. > > > > Yes, you have covered lot of points to be noted. > > > > Ravi > > > > > >> > Ok, I am in India. The tracks run through tunnels. When the train i= s > >> 2 KMs away from the tunnel, we need to switch on the light to 100% > >> brightness and when the train passes away by 2 Kms, need to dim the > >> light to 20%.Yigit, your idea of using the timetable is ok if the trai= ns > >> run on time. Well, here it is not so. Moreover if the time table is > >> changed, then all the detectors needs to be reprogrammed in the field > >> that is nearly not possible. > >> > Hope I have answered the questions. > >> > >> Nope :-). > >> > >> > >> > >> LASER <- A fixed LASER can EASILY cover 2 km in most conditions. > >> RADAR > >> LIDAR > >> Distinctive whistle > >> Radio > >> Light beam interruption. > >> Wires - electrical > >> Wires - mechanical > >> Telephone. > >> Employ somebody cheap to watch. > >> Really really really really sensitive magnetometer. > >> Smell / Odor (actually a(n unlikely) possibility!) > >> Thin pipe (air / water / vacuum) (See Gus) > >> > >> ______________________________________________ > >> > >> OK. Death of 990 cuts commences. > >> ie a FEW questions have been answered, but a full description of the > >> problem would help. > >> > >> We are the Indian Railways department / subcontractors /... > >> We are Cornish Pirates [tm] attempting to divert the train to its doom > >> on the coast so we can salvage its goods. > >> We ... > >> > >> The lights mentioned are > >> - the lighting inside the tunnel. <- presumably > >> The signalling lights at the tunnel entrance > >> - a carnival we run for train passengers > >> - advertising signs that ... > >> > >> The lights are needed because > >> - The train has no lights of its own > >> - people camp in the tunnel and the driver likes to know this. > >> - Animals may enter the tunnel > >> - Rockslides happen > >> - Terrorists happen > >> - All of these > >> - None of these, but ... > >> > >> We need to do it when the train is 2 miles way because > >> - it travels at C and that gives us 1/93,000 th of a second for the > >> lights to come on. > >> - The lights are fluorescent / CFL / beeswax tapers / oil lamps and it > >> takes several minutes for the output level to stabilise. > >> - It gives the train time to stop if the lights do not work. > >> > >> We are brighting the lights up only when the train comes because > >> - Any money we save we get to keep > >> - it increases lightbulb lifetimes. > >> - energy costs money and the department has a fixed budget > >> - none of your business*. > >> > >> We do not replace the xxx lights with LEDs that last far longer and us= e > >> far less power because ... . > >> > >> We can use radio > >> We cannot use radio because ... > >> > >> We can use wires > >> We cannot uses wires because ... > >> > >> There is good line of sight from X% of the track at about 2 km away. > >> We can't see nothin nohow. > >> > >> The train always blows a very distinctive whistle > >> The train COULD blow a distinctive whistle > >> Whistles are forbidden ... > >> > >> The train could shine a LASER > >> The train could interrupt a LASER beam. > >> The trains could trigger a LASER beam. > >> We import our atmosphere from mainland China and a LASER beam would no= t > >> reach 2 km. > >> We don't want no stinking LASERS. > >> > >> The lights need to be brighter because .... > >> We dim the lights because .... > >> > >> Why should we care? > >> > >> Other things that would be useful to know are: ... > >> > >> There are ....... other useful things that I should tell you that woul= d > >> help the solution greatly but which I will not tell you until after yo= u > >> ask ..... more questions. > >> > >> * This answer may be used elsewhere as required. > >> > >> > >> > >> Russell > >> > >> > >> > >> > >> > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .