Sensors

A critical component in train automation is sensors.  Lots is written about sensors, and I did some experiments to work out what was going to work best for me.

I tried:

• RFID.   Clearly wasn't going to work.  Takes too long to read the unique ID number.  The tags are too big, or the small ones have an even smaller range.  Too expensive.  Too unreliable.
• Infra-Red Beam Break.  This seems to work well, but it's ugly - you need the beam and the detector sticking up from the baseboard.  Its also going to take a lot of install work.
• Hall effect sensors.  I messed around with these and struggled to reliably convert the analog signal into a reliable digital on/off that was needed for the arduino's digital pins.  Until I discovered 'hall effect switches'......

The final decision.  The hall effect switch.  

Also known as "A3144" or "44E"

These are really very simple to use - 5v and ground goes in, and signal comes out.  The signal is grounded whenever a magnet passes over the switch.

The trains all need a magnet or two gluing under them.  I'm using Neodymium magnets.  These can comfortably pass over the switch 5-10mm above and make a very positive and reliable connection.  I've tested all my locomotives at full speed and it is very reliable.

Here's how they look installed on the track:

And this is how a couple of locos look with their magnets installed