gunrunnerjohn posted:That is very cool Stan! How close did you have to get the magnets to the reed switches? One concern I have is an old PW car with the shoe clipping the magnet block.
The face of the disc magnet is about 2.5mm from the edge of the reed's glass body. The disc magnets are essentially flush with the bottom of the acrylic sheet that holds them. The bottom of the acrylic sheet is about 1mm above the top of the rail(s). So there's another 1.5mm of clearance from the top of a rail to the top (highest point) of the glass body.
The nice thing about these axial magnets is you can simply stack them to make a stronger magnet. So two 3mm discs, each 1.5mm thick, snap together to make a 3mm thick disc also of 3mm diameter of course. Turned out I didn't need to do this.
Of course both magnets and reed switches (and Hall sensors) come in different grades of sensitivity. But this is a different ball game with Gauss, Tesla, etc. instead of Vots, Amps, etc.. The experiment I showed was with the parts described!
And to your point, I'm sure there are a variety of O gauge anomalies or whatever you want to call them in terms of clearance, spacing, etc.. Then there's different variants of steel rails and how that might affect magnetic fields. Another would be is Magne-traction...I wonder what kind of havoc that might wreak on trackbed magnetic sensors? 
