Limit Switch Isolator Setup

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EccentricWorkshop
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Limit Switch Isolator Setup

#1

Post by EccentricWorkshop »

I got another question today about making connections to and using the Limit Switch Isolator.

When looking at the PCB from the top with the mounting holes up, the left side if the board is for connections to physical limit switches. The top terminal in each terminal block is for the switch ground connection. The lower terminal is for the switch connection and goes into the optoisolator.

The right side terminal blocks are for connections to the Arduino limit switch pins. The top three terminals are used, one terminal is unused, and the bottom two are for ground and 5v DC from the Arduino.

As it is good practice when using opto-isolators, a separate power supply is required to drive the optoisolators themselves which is done through the top center terminal block. This provides the greatest noise isolation.

For most cases, the GRBLDuino Limit Switch Isolator will have two power sources entering the board. Both are required for the board to work properly and provide the greatest noise isolation. Should you want to only use one power supply (the Arduino) and reduce effectiveness of the opto-isolators, you can solder the jumper pads at the top right (labeled JP0/JP1).

Additional details about limit switches and isolation are explained in the GRBL wiki.
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GRBLDuino Limit Switch Isolator Datasheet.pdf
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Andy
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dkilzer
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Re: Limit Switch Isolator Setup

#2

Post by dkilzer »

My isolator hasnt yet arrived so I havent had a chance to experiment, but I was just thinking that I was planning to use some 3 wire optical limit switches I bought a while back on my new build. VCC-Signal-GND

Can I supply vcc for the optic from the isolator power supply side to avoid noise, and will it still function with signal and gnd running through the optical connector?

Or is it adding redundancy to cleaning the signal to use both optical switches and the isolator? Seems to me the optical switches could still carry noise if not run through the isolator. Mostly I just wanted to use the optical switches to avoid wear and tear on physical micros.
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EccentricWorkshop
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Re: Limit Switch Isolator Setup

#3

Post by EccentricWorkshop »

I would think you can supply power to the optic from the same power supply side. The noise really comes from the signal line and the power and ground to the optical switch are simply powering a LED of some type.

Optical limit switches can introduce noise as it is generated in the wires between the switch and the controller, not the switch itself. For best results, the isolator should be placed as close to the input pin on the controller as possible. The real purpose of optical limit switches is just as you said - reduce physical contact so less wear and tear on parts.
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Andy
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dkilzer
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Re: Limit Switch Isolator Setup

#4

Post by dkilzer »

Awesome thank you!
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