Expanding ESP32 I/O with Port Expanders: Maximum Limit?

Other Hardware General Electronics
1

I'm working on a project with an ESP32 and need to significantly increase the number of digital I/O pins.

I've considered using I2C port expanders like the PCF8575 or MCP23017, which offer 16 I/O pins each.

For cuorisity i have a Question:

  • What is the maximum number of these port expanders that I can connect to a single ESP32 via I2C?

  • Are there any limitations or considerations to keep in mind when cascading multiple expanders?

  • Are there alternative methods for expanding I/O on an ESP32 that might be more efficient or scalable?

I'd appreciate any insights or experiences from the community on this matter.

2

A very large number. Most expander chips allow up to 8 to be connected on the bus. Some chips have a second variant part number which means a further 8 of the variant chips can also be added.

Then, there are i2c multiplexer chips which give up to an extra 8 i2c channels. Each channel can have many expander chips on it. Up to 8 of the multiplexer chips can be added to the main bus. It's probably also possible to cascade the multiplexers to further increase the number of channels. Think of a tree with a single trunk, 8 large branches, 8 smaller branches for each of the larger branches, 8 twigs off each of the smaller branches, and 8 or more leaves on each twig.

3

I've used the MCP23017 and was dissapointed at the speed when used to poll a bunch of switches for debouncing purposes. Also check the newest datasheet as it's been revised to say "Pins GPA7,
GPB7 are output only for MCP23017".

4

How about the MCP23S17.
SPI can be much faster than I2C.
Leo..

5

The MCP23017 has 3 adress lines so you can configure 8 different I2C adresses.
You can use a TCA9548A I2C Multiplexer Module to get 8 I2C ports out of one I2C port.
You can put 8 TCA9548A behind a TCA9548A I2C output.
And finally, the ESP32 has two I2C ports.

But when you are planing to "significantly increase the number of I/Os" I suggest you describe your real usecase what you plan to do in total. I assume there is an easier solution than a ton of multiplexers and port expanders.

6

May consider using I2C, SPI, or USART connection to an Arduino Mega2560, Due, or Giga board for 70 (54 digital + 16 analog pins) GPIO pins on one board. The Mega is 5V and the other two are 3.3V like the ESP.