Hall End Stop

I wanted to create a non-contact hall effect end stop for my various CNC machines and 3d printers. It seemed weird that no one had tried to us a hall effect sensors with built-in temperature compensation. So I decide to build my own!

Research

I searched, read and watched the following, and found this info useful:

  1. Hall effect sensor tutorial - 3D printer end stops
  2. Op-Amps - Using Operational Amplifiers
  3. Creltek Limit Sensor 343RT

Design Plan

It seemed like the way to go was to use a temperature compensated hall effect sensor. I have upgraded my TX16S radio controller to gimbals with hall effect sensors with temperature compensation, and they completely eliminate drift compared to the original hall sensors. However, the radio control sticks use linear, bipolar hall effect sensors that sense both North and South poles of a magnet. We need a hall sensor that detects only one pole. I think that means we need unipolar linear hall sensors.

DRV5055 Hall Sensor

The TI DRV5055A3EDBZRQ1 (base name DRV5055) seemed like a good choice. This sensor is an Automotive, ratiometric linear Hall-effect sensor with analog output. Here is the data sheet

Breaking out the TI DRV5055A3EDBZRQ1 part number:

DRV5055: Base name A3: 25mV/mT, ±85mT Range E: Eco RoHS & Green? DBZ: SOT-23 Package and drawing R: Level-3-260C-168 HR MSL Peak Temp Q1: ? Automotive quality level?

Datasheet for DRV5055-Q1 Automotive Ratiometric Linear Hall Effect Sensor

Magnet orientation

Page 18 of the data sheet was very useful to determine the best orientation of the magnet and the hall effect sensor itself. This led to a determination that two boards would be needed. A sensor board could be positioned optimally for correct sensing of the magnet. A second board with adjustment potentiometer could be placed in an orientation that allowed easy access to adjust the sensing distance.

Carvey Mill

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The first machine to use this board would be a Carvey CNC mill, for the Z axis end stop. The original switch was a button style that gets crushed if the gantry over travels in the +Z direction.

KiCad

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Board milling

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Traces look good, a bit too thin maybe, used 0.38mm dia taper-stub-end mill.
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3 sets milled! That should be enough to make one or two prototype boards. Used 0.28mm dia taper-stub-end mill on two top board sets and traces were a bit wider. alt text
After filing off tabs.
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I like the RPA computer, very nice!
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No breaks in the traces that I can see. But trace continuity check will verify.

Stuffing

Not for turkeys

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Interactive BOM

I used the BOM below to handpick and place my components.

Above: Click image to access the HTML Interactive BOM (iBOM) generated by KiCad.

Comparator vs Op Amp

The TI [TLV3601DBVR(https://www.digikey.com/en/products/detail/texas-instruments/TLV3601DBVR/16669317)] might work for a faster response that an operational amplifier. But I need to verify the repeatability of my initial design above before trying a comparator.

Version 2

After testing the two board version of the Hall End Stop, I decided to build a smaller version with no potentiometer and that had the operational amplifier set to invert the output for the Carvey CNC mill. The Carvey uses an end stop circuit that needs a low voltage output when the end stop condition is met. this means that 5vdc is present when the end stop is not met and then the voltage goes low around 1 to 0vdc when the end stop is activated.

I learned that if you add two resistors and reverse the positive and negative going into the operational amplifier (op amp) from the hall effect sensor that the op amp will invert its output, cool! I found this website explained how to set up inverted op amps the best and included some calculations to amplify the output if that was needed.

Inverting Operational Amplifier

I needed a condition where if the hall effect IC saw a magnet and output 5vdc then the op amp would output ~0VDC. So I needed two resistors of the same value, I picked two 10kΩ resistors because I have a lot of them in stock.

Interactive BOM

Version 2

Above: Click image to access the HTML Interactive BOM (iBOM) generated by KiCad.

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