user8769: I have a 2008 Mac that hardly ever crashes. But from time to time (not always) it crashes (the whole computer shuts down as if the power has been cut off) when I plug in an Arduino via USB.
What could cause this?

I've done some testing and the constant in when this occurs seems to be a cheap PIR sensor from eBay. It works some of the time.
Should I get another sensor? Or is there something about PIR sensors that makes them prone to this? It has a lot of caps... Is there another kind of motion sensor?

user3538: I had this problem with a Chinese knock-off of an Arduino Nano -- looks like it was actually because I had previously installed some CH341 drivers that no longer work with Sierra.
Removing those drivers (sudo rm -r /Library/Extensions/usbserial.kext) stopped the crash (full computer shutdown when I plugged in the Arduino, even through an externally powered USB hub), but unfortunately my Mac doesn't seem to recognize the Arduino.
It looks like there is a newer version of the driver (1.4, 2017-01-11,  downloadable from here), or the 1.3 version is available as a homebrew cask if you tap that repo.
I am a little wary about installing a driver from a random Chinese site. If you want, you can unzip the driver and unpackage the .pkg file with pkgutil --expand package-name.pkg destination-folder. There are a couple subfolders including a Payload that you can inspect a little with zcat -- way over my head.
Alternatively, it looks like this repo may have a C++ driver that may work.

user19409: It could possibly be that there is a fault that is causing a short circuit. This short circuit could be in the board itself or the USB cable that connects the Arduino. The USB port on the Mac should have protection to protect against a short circuit. Your comments have indicated that you have tested for a short and found none - but this is helpful for others that are looking for a solution.
In your comments you mention that you solved this by changing the positive rail of your potentiometer from 3.3V rail to the 5V rail.

8769: <p>I have a 2008 Mac that hardly ever crashes. But from time to time (not always) it crashes (the whole computer shuts down as if the power has been cut off) when I plug in an Arduino via USB.</p>

<p>What could cause this?</p>

<hr>

<p>I've done some testing and the constant in when this occurs seems to be a cheap PIR sensor from eBay. It works some of the time.</p>

<p>Should I get another sensor? Or is there something about PIR sensors that makes them prone to this? It has a lot of caps... Is there another kind of motion sensor?</p>
 3538: <p>I had this problem with a Chinese knock-off of an Arduino Nano -- looks like it was actually because I had previously installed some CH341 drivers that no longer work with Sierra.</p>

<p>Removing those drivers (<code>sudo rm -r /Library/Extensions/usbserial.kext</code>) stopped the crash (full computer shutdown when I plugged in the Arduino, even through an externally powered USB hub), but unfortunately my Mac doesn't seem to recognize the Arduino.</p>

<p>It looks like there is a newer version of the driver (1.4, 2017-01-11,  <a href="http://www.wch.cn/download/CH341SER_MAC_ZIP.html" rel="nofollow noreferrer">downloadable from here</a>), or the 1.3 version is <a href="https://github.com/adrianmihalko/ch340g-ch34g-ch34x-mac-os-x-driver" rel="nofollow noreferrer">available as a homebrew cask</a> if you tap that repo.</p>

<p>I am a little wary about installing a driver from a random Chinese site. If you want, you can unzip the driver and unpackage the <code>.pkg</code> file with <code>pkgutil --expand package-name.pkg destination-folder</code>. There are a couple subfolders including a <code>Payload</code> that you can inspect a little with <code>zcat</code> -- way over my head.</p>

<p>Alternatively, it looks like <a href="https://github.com/z4yx/osx-ch341-serial" rel="nofollow noreferrer">this repo</a> may have a C++ driver that may work.</p>
 19409: <p>It could possibly be that there is a fault that is causing a short circuit. This short circuit could be in the board itself or the USB cable that connects the Arduino. The USB port on the Mac should have protection to protect against a short circuit. Your comments have indicated that you have tested for a short and found none - but this is helpful for others that are looking for a solution.</p>

<p>In your comments you mention that you solved this by changing the positive rail of your potentiometer from 3.3V rail to the 5V rail.</p>
