<html>
<head>
<meta content="text/html; charset=windows-1252"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Rod is 100% on target. Many logic chips cannot tolerate this
situation at all. DO NOT cut power if logic inputs are present .
Some logic families advertise provisions to offer protection for
this situation, which, in my opinion, is probably about some special
use-case situations and not at all to do with making the situation
more resilient to arbitrary configurations. <br>
<br>
-Pete<br>
<br>
<div class="moz-cite-prefix">On 03/30/2015 03:18 PM, Rodney Radford
wrote:<br>
</div>
<blockquote
cite="mid:CA+kfaxFwjumsQUkssp2TtKaYvX0G1R=EtEW-vJO5JSzAinCwQw@mail.gmail.com"
type="cite">
<div dir="ltr">Why are you trying to cut power to the chip instead
of just disabling the outputs?
<div><br>
</div>
<div>I thought the intent was to keep the chip from getting hot,
which it should only do when powering the output lines.</div>
<div><br>
</div>
<div>It is normally not wise to turn off power to chips and
still drive the inputs to those chips - it is an unexpected
operational mode and could damage the chip</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Mar 30, 2015 at 2:52 PM,
Grawburg <span dir="ltr"><<a moz-do-not-send="true"
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">
<div dir="LTR" style="font-family:Times New
Roman,Times,Serif;font-size:16px">The Enable did
disable/enable the chip which was demonstrated by setting
the Pi GPIO HIGH and the LOW. But, I wanted to actually
disable the power to the chip without disconnecting the
power source by using a transistor (which I've used for
more basic projects like powering a piezo buzzer with an
external source). <br>
<br>
I wish I could recreate what I was doing and see what slip
I made...but I'm not going to risk it :-)<br>
<br>
Brian<br>
<br>
<br>
<blockquote dir="LTR" style="border-left:2px solid
blue;margin-left:1em;padding-left:1em;font-size:13px;font-family:tahoma,helvetica,sans-serif">
<hr size="1">
<div>
<div class="h5">-----Original Message-----<br>
From: "Rodney Radford" <<a moz-do-not-send="true"
href="mailto:ncgadgetry@gmail.com" target="_blank">ncgadgetry@gmail.com</a>><br>
To: "Grawburg" <<a moz-do-not-send="true"
href="mailto:grawburg@myglnc.com" target="_blank">grawburg@myglnc.com</a>><br>
Cc: "Triangle Embedded Devices" <<a
moz-do-not-send="true"
href="mailto:TriEmbed@triembed.org"
target="_blank">TriEmbed@triembed.org</a>><br>
Date: 03/30/15 02:23 PM<br>
Subject: Re: [TriEmbed] Raspberry Pi GPIO<br>
<br>
<div dir="ltr">Never is a very long time. Regardless
of what you are doing, it is always possible for a
small wiring error to wipe out a Raspberry Pi,
Arduino, or any other computer if wired
incorrectly.
<div><br>
</div>
<div>So far I have only wiped out one Raspberry Pi
and in that case all I was doing was wiring up
some servo motors - I still don't know what i
did wrong as when I saw the magic smoke, I
quickly started pulling out wires. I checked my
schematic, all looked good, and then wired a new
Raspberry Pi up the same way (the other one was
toast) and it worked without a problem. I can
only assume I made a simple connection error.</div>
<div><br>
</div>
<div>As to what you are trying to do, could you
elaborate and provide a few more details about
what you were trying to wire up?</div>
<div><br>
</div>
<div>If you were trying to control the Enable line
of the A4988, it is an input only connection to
the A4988, so it should be treated the same way
you do the other inputs to that chip.</div>
<div><br>
</div>
</div>
<div class="gmail_extra"> <br>
<div class="gmail_quote">On Mon, Mar 30, 2015 at
2:06 PM, Grawburg <span dir="ltr"><<a
moz-do-not-send="true"
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">I will never attach
anything that even looks or smells like it
could send current back to the RPi by
connecting directly to the GPIO. I just
crapped out a Pi while working with a stepper
motor, and I'm not really sure how. I was
trying to set up a transistor to switch the
power on/off to the control board (the Enable
option still allows current to the motor) and
something happened that fried the Pi.<br>
<br>
If I can't fully isolate the Pi with a logic
level shifter or I/O port expander I don't
think I'll try to hook up a project. And I'm
sure not going to use a transistor without a
shifter.<br>
<br>
<br>
Brian Grawburg<br>
<br>
<br>
<br>
<br>
<br>
_______________________________________________<br>
Triangle, NC Embedded Computing mailing list<br>
<a moz-do-not-send="true"
href="mailto:TriEmbed@triembed.org"
target="_blank">TriEmbed@triembed.org</a><br>
<a moz-do-not-send="true"
href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org"
target="_blank">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a><br>
TriEmbed web site: <a moz-do-not-send="true"
href="http://TriEmbed.org" target="_blank">http://TriEmbed.org</a><br>
</blockquote>
</div>
<br>
</div>
</div>
</div>
</blockquote>
</div>
<br>
_______________________________________________<br>
Triangle, NC Embedded Computing mailing list<br>
<a moz-do-not-send="true"
href="mailto:TriEmbed@triembed.org">TriEmbed@triembed.org</a><br>
<a moz-do-not-send="true"
href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org"
target="_blank">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a><br>
TriEmbed web site: <a moz-do-not-send="true"
href="http://TriEmbed.org" target="_blank">http://TriEmbed.org</a><br>
<br>
</blockquote>
</div>
<br>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
Triangle, NC Embedded Computing mailing list
<a class="moz-txt-link-abbreviated" href="mailto:TriEmbed@triembed.org">TriEmbed@triembed.org</a>
<a class="moz-txt-link-freetext" href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a>
TriEmbed web site: <a class="moz-txt-link-freetext" href="http://TriEmbed.org">http://TriEmbed.org</a>
</pre>
</blockquote>
<br>
</body>
</html>