PurpleHat Trainside Sensor Introduction



The PurpleHat for the IoTT Stick is a trainside sensor that reports the distance a car is traveling. The measurement is performed by a 3D hall effect sensor that measures the magnetic field strength of a magnet that rotates with the axle. Based on the measurement, the sensor can continuously determine the rotation angle of the axis with a resolution of less than one degree. Based on the angle difference between two measurements, the time between two measurements and the wheel diameter, travel distance, direction and speed can be calculated and reported.

One of the main advantages compared to other solutions, e.g. products using optical encoders, the PurpleHat sensor is much easier to install as there is no need to run wires running underneath the car's baseboard. 

Buy it on Tindie:  N Scale  -  HO Scale Flat  -  HO Scale Vertical  -  G Scale

Example: N Scale sensor kit for vertical installation, including mounting brackets (Note: IoTT Stick is not included in kit)

N scale sensor kit

Watch these videos for more information:

How to use a 3D hall sensor to measure rotation angle

Analyzing the precision of the PurpleHat measuring cell

Using the PurpleHat for speed matching

The PurpleHat also has an interface for adding an Inertial Measurement Unit, which allows to measure yaw, pitch and roll of the car. With a known starting position, the PurpleHat therefore can report the train position or even be used to analyze the geometry of the track it is traveling on.

At this time, the IMU code is not officially released, but the idea has been demonstrated in these videos:

Layout GPS demonstration

Layout GPS technical explanations