hall effect switch

Posted on Feb 5, 2014

For the limit switches on a custom 3D printer I`m designing, I want to try out some contactless sensors. I have chosen to use hall effect sensors, which are sensitive to a magnetic field. There are three different types of these sensors available. First, there`s the omnipolar hall sensor, which turns on when a magnet comes in its vicinity. Next is

hall effect switch
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the unipolar one, which turns on as long as a specific magnetic pole is close enough, which pole depends on the sensor. Finally, there`s the bipolar hall effect sensor, which latches on when one pole comes close and only turns off when it senses the other pole. The sensors that I am using for my circuit is an Allegro A3144, an unipolar sensor. These are no longer manufactured, however eBay is chock full of them and they can be had for less than ‚¬0. 20 each. They come in a miniature TO-92-like package, as seen in the picture below. As a visual indication of the sensor`s status, I want two LEDs, one each for the triggered and off state. Since the A3144 has an open collector output, driving a LED from the output is only possible when the sensor is triggered. In order to drive both LEDs either a buffer or an inverter is required. One option is to use an N-channel MOSFET for the off LED and connect the triggeredLED straight to the A3144`s output. Apart from the MOSFET, this would also require a resistor to the MOSFET`s gate. A alternative which uses less parts is the versatile 74LVC1G58. This is a configurable logic chip with 3 inputs, which has ±24 mA output drive and comes in a tiny SOT23-6 package. Best of all: when configured as an inverter, the pins are grouped together such that the chip can be soldered on a standard breadboard. You can find the schematic for my simple hall effect switch below. I used SMD components for...

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