[TriEmbed] Raspberry Pi & Port Expanders

[Jim Ray]

Speaking of isolation and GPIO, is there a recommended relay either solid state or mechanic that you recommend to switch a 500W load whether AC or DC? It would be way cool if it were small enough to plug into the little Cannakit breadboard expansion thingie.

From: TriEmbed [mailto:triembed-bounces at triembed.org] On Behalf Of Carl Nobile via TriEmbed
Sent: Monday, November 09, 2015 9:54 AM
To: Robert Gasiorowski
Cc: Triangle Embedded Devices
Subject: Re: [TriEmbed] Raspberry Pi & Port Expanders

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<mailto: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<mailto: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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