[TriEmbed] Raspberry Pi GPIO

[Pete Soper]

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.

-Pete

On 03/30/2015 03:18 PM, Rodney Radford wrote:
> Why are you trying to cut power to the chip instead of just disabling 
> the outputs?
>
> I thought the intent was to keep the chip from getting hot, which it 
> should only do when powering the output lines.
>
> 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
>
> On Mon, Mar 30, 2015 at 2:52 PM, Grawburg <grawburg at myglnc.com 
> <mailto:grawburg at myglnc.com>> wrote:
>
>     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).
>
>     I wish I could recreate what I was doing and see what slip I
>     made...but I'm not going to risk it :-)
>
>     Brian
>
>
>         ------------------------------------------------------------------------
>         -----Original Message-----
>         From: "Rodney Radford" <ncgadgetry at gmail.com
>         <mailto:ncgadgetry at gmail.com>>
>         To: "Grawburg" <grawburg at myglnc.com <mailto:grawburg at myglnc.com>>
>         Cc: "Triangle Embedded Devices" <TriEmbed at triembed.org
>         <mailto:TriEmbed at triembed.org>>
>         Date: 03/30/15 02:23 PM
>         Subject: Re: [TriEmbed] Raspberry Pi GPIO
>
>         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.
>
>         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.
>
>         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?
>
>         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.
>
>
>         On Mon, Mar 30, 2015 at 2:06 PM, Grawburg <grawburg at myglnc.com
>         <mailto:grawburg at myglnc.com>> wrote:
>
>             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.
>
>             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.
>
>
>             Brian Grawburg
>
>
>
>
>
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