Hall Effect Switch - Turnout Position Detector

  This circuit uses a small magnet and a Hall Effect switch to detect the position of a turnout's throwbar. The detector can be used monitor turnouts that have manual throws but need to control LEDs on a track diagram or have an input to an interlocking or CTC system.

  The circuit uses a magnetically sensitive Hall Effect switch. In this circuit, when the magnet is in close proximity to IC 1, D1 will turn off and D2 will turn on.

  An Allegro MicroSystems - A1126 ( DigiKey part 620-1423-ND ) switch was used for this circuit. The A1126 is not magnetically polarity sensitive.

  There are many other hall effect switches available that can be used for this application. These devices are essentially solid state reed switches.

  The switched current capacity of the A1126 switch is 30 milliamps. Greater capacities can be had by adding an external transistor or other driver.

A1126 Case Dimensions (mm)

Terminal 1 - SUPPLY     Terminal 2 - GROUND     Terminal 3 - OUTPUT

The small square in the centre of the case is the position of the hall sensing element.

Test Installation

  The following is a users test mounting using a power operated, Kato Unitrack #6 turnout and a rare earth magnet. The hall-effect switch changes state at about half way through the throwbar travel. LEDs on a remote panel show the position of the turnout.

  The magnet has been attached with contact cement and painted black. The position of the hall switch allows the turnout to be thrown manualy without it being in the way.

Rare Earth Magnets

  Rare earth magnets are very strong and may be unsuitable for use on turnouts that have short throws. The throwbar travel of KATO turnout is long compared to other designs so this is not a problem.

Strip Magnets

  Sections of strip or fridge magnets can also be use with this circuit.

  Strip magnets are made up of many small magnets formed into strips or sheets. The strength of small sections will be weak but the throwbar travel of most turnouts is quite short so this should not be a problem.

  Testing will be needed to determine how to cut the strips to produce useable magnet sections. Their orientation in relation to the switch will also have to be tested if a polarity sensitive hall effect switch is used.

  The A1126 used in designing this circuit is not magnetically polarity sensitive.

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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06 November, 2016