Add MCP23017 port expander support as a lua module

[plomi-net]

Missing feature

Hello,
I would like to contribute a few things to this great project.

I saw that there are already issues for the MCP23017 Port Expander. Unfortunately I didn't find any Lua or C modules in the current dev branch.

Without looking into the issues, I just created a module in Lua for the MCP23017.
Now I would like to learn more and adapt the module to become part of this project.

Justification

This module can help other IoT developers to easily provide more GPIO pins, for example to control a relays card.

Workarounds

I am not sure which workaround represents a good solution.

Kind regards,
Marcel

[marcelstoer]

Contributions are welcome. Consider #3034.

[jmd13391]

@plomi-net, Have you see this?

MCP23008 Module

I am currently using this Lua Module to extend the ESP8266 GPIO with great success.

[plomi-net]

Hi @jmd13391, @marcelstoer

Thank you very much for your comment.
I had seen the module for the MCP23008 chip and that inspired me to create a module for the MCP23017.

For my project I need 16 channels, theoretically 128 pins would be possible with 8 MCP23017.
I could also have used two MCP23008.

I will refactor my module in the next few days and then provide it.

[plomi-net]

Hi,
some time has passed, now.

I have attached the program code with a pull request.
I hope the refactor succeeded and helps someone to extend the nodemcu.
If anyone has any comments or feedback, please let me know.

thanks a lot