Track Sensor

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The track sensors are simply Hall Effect sensors that detect magnetic fields.  In order for them to work, you'll need to attach magnets to the bottom of your engines.  Some of my magnets are 2 mm thick and some are only 1 mm thick.  It just depends on what vehicle you're attaching the magnets to as to what size you'll need.  The A3144 sensors can detect a magnetic field about 1/2 inch away in plain air, but when placed under track, that distance is lowered, so you'll need to get them as close to the underside of the track as possible.   

Basic Instructions:

It may also be helpful to have the mcp23017 pintout handy [clik here]