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I'm working on a project using a NodeMCU and am quickly running out of GPIO pins. I'm trying to decide which way to go to complete it.

Right now, I have the MCU connected to a MAX31856 PT100 thermocouple (SPI), a PWM output, a transistor (acting as a switch), a single button and a single LED. I'm needing to add at least 2 more of the MAX31856, a display (either I2C or SPI) and a rotary encoder/button.

I've looked into GPIO expanders, but I'm doubtful that the available libraries for the additional hardware will work through the expanders. I have a Mega that will work without a doubt, but then I will have issues with WiFi & MQTT. I looked at the Mega's with onboard WiFi, but I got so confused in reading how to program it, setting the DIP switches, etc that it doesn't seem like a valid choice.

Can anyone offer guidance?

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    MAX31856 is SPI so use an SPI display
    – Juraj ♦
    Aug 22, 2019 at 11:29
  • i would move less-used interface hardware to the app to keep cost down and free up pins. i would also use i2c everything. You can use GPIO10 as an input. you can use A0 for the button. You can use GPIO3 for input and GPIO1 for output if you don't use Serial. You can use GPIO0 for the rotary encoder button, if it's never pressed on boot.
    – dandavis
    Aug 23, 2019 at 18:20

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Two main solutions comes to my mind:

  1. GPIO expander (as you mentioned). It is really easy to use them as digital inputs or outputs. So you can connect button, LED, transistor and maybe even display (you did not specified type of the display, so I assume standard LCD 1602 or 2004 display). You can also connect SPI-CS signals to the expander, but this depends on used libraries...
  2. Auxiliary Arduino e.g. Nano. Arduino can be used for measurement of the temperature and other stuff and NodeMCU for communication. In this case you have to implement some kind of communication between these two boards (SPI, I2C or UART).
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