Sensor Board Installation

The PurpleHat board is available in two version, one for flat mount and one for vertical mount. The two boards are identical except for the placement of the hall sensor on the board. The flat mount version has the sensor in the middle of the board, so that it can be installed along the centerline of the car and the sensor will be above the middle of the axle. The vertical mount version has the sensor to the side, so that if it is installed vertically, the sensor is as close as possible to the base plate of the car, and therefore the distanced to the axle is minimized.

Sensor position flat mount Sensor placement for vertical mount

The vertical mount version is intended for smaller scales, i.e. N scale, where the width of the sensor, including IoTT Stick is more than the width of the car. In order to fit the sensor inside the car, it needs to be turned 90 degrees. If there is more space available, flat mount is probably the preferred method of installation as it lowers the center of gravity of the car. However, the HO kit is available in both versions, so that it is possible to have the sensor upright and cut the sidewall of the car open to allow the display to be seen as the car travels by.

Flat installation

Place the sensor board on the base plate of the car so that the 3D hall sensor chip is directly above the magnet equipped axle. If it is not possible to place it directly above the axle, place it as close as possible. The 3D hall sensor is rather tolerant, so if it is a few millimeters to any direction, it should still work.

If there is metal ballast between the magnet and the sensor, it should be removed as it is weakening the strength of the magnetic field. There is no need to remove the entire ballast, it is sufficient to just cut an opening of about half an inch around the location of the hall sensor.  

To secure the PCB in place, use two pieces of double sides tape to stick it to the base plate. it is best to place the tape strips close to the ends of the sensor PCB in a location where it sits firmly on the base plate of the car. If there are any plastic parts sticking out from the base plate, you may want to file them down.

PurpleHat in flat position on freight car

If the base plate is of conductive material, or if the sensor PCB sits on a steel ballast or other conductive material, you should place some electrical tape or another insulating layer between the PCB and the base plate to make sure that no solder eyes of the sensor PCB create an electrical contact with the base plate. 

Vertical installation

Use the vertical mounting brackets that come with the kit to vertically install the sensor PCB. Identify the correct location of the brackets and use some double sided tape to stick them to the base plate. Once installed, use some glue to secure the sensor PCB in the correct location.

PurpleHat in vertical position on HO freight car

For N scale installations it is an option to cut the sensor PCB in two parts and use a pin header to adjust the location of the IoTT Stick to the center line of the car. Cut the PCB carefully between the first and second row of soldering eyes. Then place the two halves as needed and use pins or short wire pieces to reconnect the two pieces.

N scale split installationN scale split installationN scale split installation

Support Battery Installation

If there is enough room in your car, you can optionally install an additional battery to the sensor PCB. Any 3.7V LiIon battery will work. Electrically, it is connected in parallel to the internal IoTT Stick battery and it is charged and protected by the built-in BMS of the IoTT Stick.

Battery installationBattery installation

Solder the 2-pin pin header to the sensor PCB, on either of the connection points labeled + and - based on what fits best to the location of the battery. Then connect the battery to the pin header.

Warning: Before connecting, make sure the  additional battery is charged to about the same voltage like the built-in battery of the IoTT Stick to avoid high initial currents when connecting the additional battery. Also make sure the polarity is correct!

Axle Magnet Installation

The PurpleHat sensor chip needs a magnetic field that is radial to the axle, so that it changes from full north to south with every half revolution of the axle. This can easily be provided by installing two round magnets, one on each side of the axle. The magnets need to be small enough to not touch anything around the axle, so that the axle can rotate freely all the time.

Smaller scales (N, HO)

Recommended magnet sizes for smaller scales are 3 x 2 mm for HO and 2 x 1 mm for N scale. To install them on the axle, it is best to use a file to make a flat spot on each side of the axle and then just place one magnet on each side of the axle. The opposing poles of the magnets will make sure that both magnets are pulled towards the axle, while the flat spot ensures that they can't bounce to the side. In most cases, this setup will work without further fixation of the magnets, however, in order to secure them it might be a good idea to add a drop of glue on the flat spot.

HO scale axle with magnetsMagnets on N scale axle

Watch this video for a demonstration of the installation of the magnets

Large scale

Recommended magnet size for G scale: 12 x 3 mm. To install the large magnets on the axle, the G scale kit comes with two magnet holders, one for each side of the axle. Simply clip the two holders on the axle, and that's it, at least if your car is equipped with a 6mm axle. If your car has an axle with a lower diameter, you may add a few layers of scotch tape to make sure the holders sit firmly on the axle.

12mm magnets mounted on G scale axleMagnets installed on G scale axle with mounting brackets

Also for G scale, it might be a good idea to secure the holders with some hot glue to prevent magnets from getting lost somewhere on the layout.


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