I2C on Pico W RP2040

emefff · November 24, 2022, 6:11pm

Hi,

has anyone been able to get I2C running on RP2040? From what I’ve read it should work. If I add an I2C bus definition (with or without sensor definition) my Pico W does not boot anymore. Not even a log appears. If I uncomment it, it boots.

Mario.

nickrout · November 24, 2022, 6:48pm

As the docs say

Support for all aspects of ESPHome on the RP2040 is still in development. Please search for or create an issue if you encounter an unknown problem.

emefff · November 25, 2022, 6:48am

Before submitting a bug report I wanted to make sure, that I do not have a dud RP2040. I will try a second Pico W today.

emefff · November 26, 2022, 10:06am

A second Pico W shows the same behavior (see bug report Activating I2C --> Pico W does not boot correctly · Issue #3838 · esphome/issues · GitHub)

carealto · May 16, 2023, 8:54pm

Having the same issue

simon-77 · July 23, 2024, 3:29pm

Hi, I also have troubles getting I2C on my Pico W to work with ESPhome.

First of all, I found some information that only the I2C0 hardware is usable:

I have connected 4k7 pull-ups to GPIO4 & GPIO5 (I2C0), but I always get an error:
Recovery: failed, SDA is held low on the bus

Using my Multimeter I can measure stable 3.3V on both pins.

@emefff could resolve the issues by using the GPIO numbers for pin 21 & 20.

github.com/esphome/issues

Activating I2C --> Pico W RP2040 does not boot correctly

opened 09:58AM - 26 Nov 22 UTC

closed 04:18PM - 15 Dec 22 UTC

emefff

### The problem Hi, first of all, I am very happy, that RP2040 is included in …ESPHome now. Very promising and also cheaper :-). I tried I2C on two different Pico Ws now. Thus, I am fairly sure they are ok. Defining I2C the usual way via something like: i2c: sda: 26 scl: 27 scan: true id: bus_a compiles successfully, OTA also works (see attached logs_test_upload). But after the upload, the Pico W does not boot or connect to ESPHome (Dashboard in HA shows OFFLINE). Unplugging the Pico and rebooting shows ONLINE, but the log tells me 'no connection' (see logs_test_logs). Also, uploaded code (like a blinking led or Dallas DS18B20) doesn't seem to be running. Maybe it is in some sort of brown-out-state? I was under the impression I2C should already work? Or am I too early? Any hints appreciated, thanks Mario. [logs_test_upload.txt](https://github.com/esphome/issues/files/10096009/logs_test_upload.txt) [logs_test_logs.txt](https://github.com/esphome/issues/files/10096010/logs_test_logs.txt) ### Which version of ESPHome has the issue? 2022.11.3 ### What type of installation are you using? Home Assistant Add-on ### Which version of Home Assistant has the issue? 2022.11.4 ### What platform are you using? RP2040 ### Board Pico W ### Component causing the issue i2c ### Example YAML snippet ```yaml esphome: name: test rp2040: board: rpipicow framework: # Required until https://github.com/platformio/platform-raspberrypi/pull/36 is merged platform_version: https://github.com/maxgerhardt/platform-raspberrypi.git # Enable logging logger: # Enable Home Assistant API api: encryption: key: "REDACTED" ota: password: "REDACTED" wifi: ssid: !secret wifi_ssid password: !secret wifi_password # Enable fallback hotspot in case wifi connection fails ap: ssid: "Test Fallback Hotspot" password: "REDACTED" i2c: sda: 26 scl: 27 scan: true id: bus_a ``` ### Anything in the logs that might be useful for us? _No response_ ### Additional information _No response_

When using these GPIOs, I also measure 3.3V on these pins (i.e. internal pull-ups are activated successfully), but I also have the same issue regarding “SDA is held low”

I tried multiple pin-pairs of the i2c0 peripheral and 3 different pico boards in total, no external components are connected on the i2c bus, beside the pull-up resistors on GPIO4 & GPIO5.

Does anyone have a clue why I am getting these errors?

ESPHome version 2024.7.1

Configuration (additional to default config for Pi Pico W):

i2c:
  sda: GPIO20 
  scl: GPIO21 
  scan: true
  id: bus_a

ESPHome log:

17:28:50][I][app:100]: ESPHome version 2024.7.1 compiled on Jul 23 2024, 17:19:07
[17:28:50][C][wifi:599]: WiFi:
[17:28:50][C][wifi:427]:   Local MAC: D8:3A:DD:21:C3:F8
[17:28:50][C][wifi:432]:   SSID: [redacted]
[17:28:50][C][wifi:435]:   IP Address: 10.69.1.201
[17:28:50][C][wifi:438]:   BSSID: [redacted]
[17:28:50][C][wifi:440]:   Hostname: 'test-aqm'
[17:28:50][C][wifi:442]:   Signal strength: -37 dB ▂▄▆█
[17:28:50][C][wifi:446]:   Channel: 6
[17:28:50][C][wifi:447]:   Subnet: 255.255.0.0
[17:28:50][C][wifi:448]:   Gateway: 10.69.0.1
[17:28:50][C][wifi:449]:   DNS1: 10.69.0.1
[17:28:50][C][wifi:450]:   DNS2: 0.0.0.0
[17:28:50][C][logger:185]: Logger:
[17:28:50][C][logger:186]:   Level: DEBUG
[17:28:50][C][logger:188]:   Log Baud Rate: 115200
[17:28:50][C][logger:189]:   Hardware UART: USB_CDC
[17:28:50][C][i2c.arduino:071]: I2C Bus:
[17:28:50][C][i2c.arduino:072]:   SDA Pin: GPIO20
[17:28:50][C][i2c.arduino:073]:   SCL Pin: GPIO21
[17:28:50][C][i2c.arduino:074]:   Frequency: 50000 Hz
[17:28:50][C][i2c.arduino:092]:   Recovery: failed, SDA is held low on the bus
[17:28:50][I][i2c.arduino:096]: Results from i2c bus scan:
[17:28:50][I][i2c.arduino:098]: Found no i2c devices!
[17:28:50][C][mdns:116]: mDNS:
[17:28:50][C][mdns:117]:   Hostname: test-aqm
[17:28:50][C][esphome.ota:073]: Over-The-Air updates:
[17:28:50][C][esphome.ota:074]:   Address: test-aqm.local:2040
[17:28:50][C][esphome.ota:075]:   Version: 2
[17:28:50][C][esphome.ota:078]:   Password configured
[17:28:50][C][safe_mode:018]: Safe Mode:
[17:28:50][C][safe_mode:019]:   Boot considered successful after 60 seconds
[17:28:50][C][safe_mode:021]:   Invoke after 10 boot attempts
[17:28:50][C][safe_mode:022]:   Remain in safe mode for 300 seconds
[17:28:50][W][safe_mode:028]: Last reset occurred too quickly; safe mode will be invoked in 8 restarts
[17:28:50][C][api:139]: API Server:
[17:28:50][C][api:140]:   Address: test-aqm.local:6053
[17:28:50][C][api:142]:   Using noise encryption: YES

Ayfid · June 29, 2025, 5:11am

@simon-77 Did you find a solution to this? I am having the exact same problem.

simon-77 · June 29, 2025, 6:22am

Nope, unfortunatelly not.

I tried it at some point again with a newer version, but I still can’t get it to work …

simon-77 · November 22, 2025, 11:48am

I have to admit: the reason my I2C device did not work was that I mixed up the SCL & SDA lines while connecting the device

… however, the log output regarding SDA is held low then brought my attention away from the connected device to getting rid of this log message by not connecting any device to the pi pico.

Turns out, when connecting a I2C device (correctly) to the pico, this log line is always produced wrongfully, although the I2C devices are working (and also the address scan is working).

Cheers
Simon