Scan does, driver doesn't find chip

[muranyia]

I have a custom build Adafruit CircuitPython 7.3.0-alpha.0-38-g862210b3f-dirty on 2022-03-13; Adafruit Trinket M0 with samd21e18 with 24lc32 frozen.

I can find the chip via I2C scan at the address 0x50 but the driver doesn't find it there.

import board
import time
import adafruit_24lc32
import supervisor

supervisor.disable_autoreload()

i2c = board.I2C()

#  scan I2C
while not i2c.try_lock():
    pass
try:
    while True:
        print(
            "I2C addresses found:",
            [hex(device_address) for device_address in i2c.scan()],
        )
        time.sleep(1)
finally:  # unlock the i2c bus when ctrl-c'ing out of the loop
    i2c.unlock()

#  setup for EEPROM
eeprom = adafruit_24lc32.EEPROM_I2C(i2c_bus=i2c)

I2C addresses found: ['0x50']

Traceback (most recent call last):
  File "code.py", line 24, in <module>
  File "adafruit_24lc32.py", line 240, in __init__
ValueError: No I2C device at address: 0x50

[tekktrik]

Does that code work if it's not baked into the UF2?

[muranyia]

After adding adafruit_bus_device too, I get:

Traceback (most recent call last):
  File "code.py", line 49, in <module>
  File "adafruit_24lc32.py", line 240, in __init__
  File "/lib/adafruit_bus_device/i2c_device.py", line 61, in __init__
  File "/lib/adafruit_bus_device/i2c_device.py", line 183, in __probe_for_device
ValueError: No I2C device at address: 0x50

Latest firmware and bundle.

[muranyia]

I noticed that i2c.scan() picks up the chip only on a fraction of the tries. I'm new to i2c so I thought it was normal but an mcp23017 is picked up on every try so I suspect this is not the right behavior. I think the pulls are OK: addresses and WP are pulled down directly, SCL and SCK are pulled up through 5k resistors. Could it be a faulty chip, or is my circuit wrong, or...?

[FoamyGuy]

@muranyia if your up for it I would recomend to join our discord https://adafruit.it/discord there is a help-with-circuitpython channel where you can get help troubleshooting things.

can you post a picture of your wiring? also let us know what specific device you are connecting to, is it this? https://www.adafruit.com/product/5146

[muranyia]

The device is a bare DIL 24lc32a and the wiring is like this. Never used discord but I'll try to figure it out.

[muranyia]

No reply on discord... I figured out that once I connect an ssd1306 device to the bus, the 24lc32 gets picked up too. When I disconnect the clock pin of the ssd1306 the board loses the 24lc32 too. Tried with a Trinket M0 and a Feather M4 Express, same behavior.

[muranyia]

Tried with different pullups, no dice. The question is, what does the ssd1306 do to the bus that makes it work?

[tekktrik]

Wait, SCK? Did you mean SDA?

[tekktrik]

You could also try 10k resistors. Also try another 24LC32 as well just to rule out something wrong with that unit.

[muranyia]

Yes I meant SDA... sry. Will try with 10k. 5k and 2k didn't work.

[tekktrik]

You could also try changing the frequency using the frequency argument:

i2c = busio.I2C(board.SCL, board.SDA, frequency=50000) # Set frequency to 50 kHz

Not sure if that will work, but it's something to try.

[muranyia]

frequency=50000 throws Unsupported baudrate. N.B. with the ssd1306 connected I had no problems going up to 400kHz. I only have an issue when the ssd1306 is not on the bus. But! The 10k pullups seem to work. I test a few things (my display is not working right now) and if everything is fine I will come back to close the issue.

[tekktrik]

Sounds great! Glad it's working out so far!

[tekktrik]

Did your tests end up working out?

[muranyia]

Couldn't test extensively but len() gives the right length so I assume everything is fine. Thanks again!