lego magnetic presence detector

[XG BC]

As promised in my winter ski resort layout topic over on the town forum 

here is a detailed look at my magnetic lego train sensor. the construction looks fairly stealthy:

it really only needs two wires but the other wires are for powering the 9v track. the actual sensor is underneath the brown plate.

the sensor consists of stripped wires that are stuck inbetween the plate and the rail sleeper. the two wires are normally insulated from each other.

 

the other plates are to prevent the magnet from sliding out of the sensor part. the magnet is a small round neodynium magnet. if a train runs over it it pulls that magnet up thus completing the cirquit. resetting is done via the magnet falling back down.

the trains buffer magnet isnt really strong enough to pull the magnet up so i just stuck another one to the bottom that helps attract the rail magnet (this is just stuck on there magnetically no glue used).

 

how it looks with a wagon there. the sensor isnt silent. it makes a klack sound as the magnet rises up and sticks to the top plate.

a small cirquit diagram to see all the components of that system

hope this helps someone!

[zephyr1934]

Nice! You've essentially made your own reed switch

[XG BC]

thanks. it is essentially a reed switch just different true .

[GoHabsGo]

Good idea!

[JopieK]

Works really well, I also do it like this. B.t.w. if you experiment a little with it you find out that to detect motors you don't need additional magnets, but of course it depends on what you want to detect.

[XG BC]

i want to detect the ends of the train. i think the buffer magnet alone works too but not shure. on one side of it would be a bad time if the sensor fails as the table ends there. may need to build a bumper that can take the impact should this ever happen.

[Toastie]

1 hour ago, XG BC said:

may need to build a bumper that can take the impact should this ever happen.

I am using some liftage to accomplish that - the train slides onto some sloped elevation until the wheels run free. Only works on the engine of course; in case there are carriages at the end, these need to have clearance ... so maybe not that good of an option.

Best,
Thorsten

[XG BC]

the side that has the carridge runs into the wall if anything happens anyways but the other side needs a bumper for shure. there isnt too much inertia as the loco is fairly small and the wagon is relatively light.

[Paperinik77pk]

Nice solution!!! It's good to see some experiments like this one!!! 

 

Ciao!

Davide

[zephyr1934]

19 hours ago, XG BC said:

the side that has the carridge runs into the wall if anything happens anyways but the other side needs a bumper for shure. there isnt too much inertia as the loco is fairly small and the wagon is relatively light.

Toastie's solution is a nice failsafe, but you could also do a hidden failsafe using a bit of tape in the rail connection to isolate the last bit of track (either direction) and a diode to make the track beyond "one way" power. That's one of the nice features of 9v

[XG BC]

1 hour ago, zephyr1934 said:

Toastie's solution is a nice failsafe, but you could also do a hidden failsafe using a bit of tape in the rail connection to isolate the last bit of track (either direction) and a diode to make the track beyond "one way" power. That's one of the nice features of 9v

could do that aswell true. but i have already made a bumper (was required anyways so why not make it sturdy enough to stop the train). that thing should never occur anyways as the system has one moving part and is releiable.

[ThePhatController]

17 hours ago, zephyr1934 said:

Toastie's solution is a nice failsafe, but you could also do a hidden failsafe using a bit of tape in the rail connection to isolate the last bit of track (either direction) and a diode to make the track beyond "one way" power. That's one of the nice features of 9v

Very clever! I might use this trick on my 12v layout.