Using an MCP23017 with a Pi Pico [SOLVED]

[mike632t]

I was just wondering if any one had got this to work, I've tried several different pairs of pins but i2c.scan() doesn't return anything.

Code: Select all

import machine
i2c = machine.I2C(0, sda=machine.Pin(8), scl=machine.Pin(9))
i2c.scan()

It doesn't make any different if I specify the freq as well.

Code: Select all

import machine
i2c=machine.I2C(0, sda=machine.Pin(8), scl=machine.Pin(9), freq=400000)
i2c.scan()

I'm obviously missing something, the MCP23017 works fine with various models of Raspberry Pi, Pi Zero, and a WiPy2.0. The only thing I can think of is that the Pico needs external pull up resistors, but my google fu is weak today and I've not found a definite answer (resistors on their way just in case).

Thanks

[scotty101]

The source code for the MicroPython port indicates that the internal pull up resistors configured when you use machine.I2C so external ones shouldn't be needed.

Check your wiring, especially power and ground.

[pic0]

Hi,

The source code for the MicroPython port indicates that the internal pull up resistors configured when you use machine.I2C so external ones shouldn't be needed.

As stated here the internal pull ups are vrery weak, so you should add external resistors.

[mike632t]

Added a couple of external 10K pull up resistors and .. success!!

Code: Select all

>>> i2c = machine.I2C(0, sda=machine.Pin(8), scl=machine.Pin(9))
>>> i2c.scan()
[33]
>>> hex(33)
'0x21'
>>>

Actually discovered that I only needed a single 10K pull up on SCL (MCP23017 pin 12)