<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body >Also, be careful of ground loop, tie the ground lines together as close to the power sources as possible. I think none of the pi's I/o are 5v tolerant, so make sure they are either open drain or level shifted.<br><br><div>-------- Original message --------</div><div>From: Glen Smith <mrglenasmith@gmail.com> </div><div>Date:09/17/2014 12:05 PM (GMT-05:00) </div><div>To: Grawburg <grawburg@myglnc.com> </div><div>Cc: Triangle Embedded Devices <TriEmbed@triembed.org> </div><div>Subject: Re: [TriEmbed] RPi & Port Expander Grounds </div><div><br></div><div dir="ltr"><div><div>No,<br><br></div>The grounds should always be tied together. Otherwise you can run into very strange results.<br><br></div>Glen<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Sep 17, 2014 at 12:03 PM, Grawburg <span dir="ltr"><<a href="mailto:grawburg@myglnc.com" target="_blank">grawburg@myglnc.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Am I correct (based upon previous posts) that when I use a port expander with my Pi and use an external power source for the devices connected to the expander, I should always use the ground on the Pi. Therefore, the ground of an external 5 VDC is not utilized. <br>
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Thanks,<br>
Brian<br>
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