Garden Railway Sensors

Posted on Feb 7, 2014

A sensor in garden railway applications. Hall Effect sensors are the electronic equivalent of a reed switch. You can think of them as a cross between a reed switch and a transistor. They are frequently used to determine the rotational speed of a spinning device, such as the platter of a hard drive or the drive shaft of an automobile. A small magnet is attached to the spinning object so that it goes

Garden Railway Sensors
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past the Hall sensor as it rotates. The sensor sends one pulse to a counting circuit each time the magnet passes. I have also seen computer keyboards that have a magnet under each key that comes close to a Hall sensor on each key press. A nice system as there are no mechanical switches to wear out! This photo shows the bottom side of a computer`s floppy disk drive. The rotational speed of the platter is measured by the small Hall Effect sensor that you can see at the 7:00 position. Just to its right you can see the small magnet that is attached to the platter. By measuring the time needed for each rotation the speed can be measured and adjusted by the electronics on the drive. In garden railway applications Hall Effect sensors can be used in most places where a reed switch would be employed. Their main advantage is their small size and lack of mechanical parts that are prone to failure. On the down side you must run three wire cable to them and it can take a bit more circuitry to connect them to another device. In addition most Hall Effect sensors, such as the one used in this article, respond to only one of a magnet`s poles. This forces us to be a bit more careful when mounting magnets that will stimulate a Hall Effect sensor. The device I am working with here is Panasonic part number DN6848-ND. It is available from Digi-Key ( ) for a little more than $1. 00 each in small quantities. The open collector output of this...

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