[TriEmbed] Raspberry Pi & Port Expanders

Carl Nobile carl.nobile at gmail.com
Mon Nov 9 08:53:38 CST 2015


Brian,

The only reason you may not want to use a port expander chip is if there
are enough GPIO pins on the RPi to do what you need and in general serial
communication whether it's I2Cor SPI will be slower than a parallel setup
which you would get directly off the GPIO pins. I don't think speed is an
issue with you though. The newer RPis have more pins on them and may lessen
the need for port expander chips. Anyway, I feel you are doing fine the way
you are.

~Carl


On Mon, Nov 9, 2015 at 9:45 AM, Robert Gasiorowski via TriEmbed <
triembed at triembed.org> wrote:

> Yes there is, MCP23S17 and MCP23S08, both SPI.
>
> Rob.
>
> On Mon, Nov 9, 2015 at 9:22 AM, Grawburg via TriEmbed <
> triembed at triembed.org> wrote:
>
>> as many of you already know I'm a big fan of using an I/O port expander
>> (MCP23017 or MCP23008) when I'm working with anything that uses voltage
>> other than 3.3 VDC. I want to make sure the Pi is fully isolated from the
>> devices.  I realize that the Python coding is a bit more involved when
>> using an I2C device and that it doesn't currently run on Python 3. I just
>> think the trade-off with protecting the Pi is worth it.  Now, here's my
>> question: Is there a situation when I should not use an I2C chip, keeping
>> in mind the projects I'm dealing with are, by most standards, relatively
>> basic?
>>
>> At tonight's meeting I'll have part of my pipeline valve and pump project
>> that is using a single MCP23017 because I need more than 8 I/O pins. If
>> there is an interesting alternative to the I2C I'd like to know about it.
>>
>>
>> Thanks,
>> Brian Grawburg
>>
>>
>>
>>
>>
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>
>
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-- 
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Carl J. Nobile (Software Engineer)
carl.nobile at gmail.com
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