Troubleshooting • Re: CM4 I2C i2cdetect shows no addresses

RPi GPIO are 3.3V logic levels.
In case your relay board uses 5V logic you will have to use an I2C voltage level translater.

Applying 5V to the GPIO can/will kill them!
Sorry, I did not check your 'boot metthod link'. Use an official OS image, boot from uSD.

I2C-1 is the interface of interrest, I2C-20/21 are DDC1/DDC2 - related to HDMI.
To enable i2c-1 you will have to enable i2c_arm via config.txt.

Which I/O board do you have?

Yes, hence the logic level converter. The boot method can also be found in the official documentation, and I am using an official OS image from the official RPi imager.

I mentioned in the original post confirming i2c_arm has been enabled through various means including editing config.txt, the pastebin link contains the file as well as "gpio readall" and "pinctrl get" outputs.

I have the CM4 IO Board, as in the IO board 4.

Test independent of your device.
Short SDA to ground and i2cdetect should report all addresses as present.
Short SCL to ground and i2cdetect should run very slowly (~1 sec per address) and nothing be detected.
Repeat on both sides of the voltage shifter.
If that is all working, then look at your device and why it isn't responding. Probing MCP23017's is fairly easy. Are they actually powered properly?

3v3 side: As you described, SCL to ground runs slowly and SDA to ground shows all addresses although 0x31 and 0x32 didn't appear in the first run, did on all runs following.
5v side: No detection for either, similar to what the logic analyzer says - so no SDA nor SCL signals are getting through though the voltages read properly. I suppose I'm then either doing something wrong or the converter is bad.

Here's an artistic renditionMCP-wise, there are two on board (sorry for formatting)
MCP23017 #1: GPB0-7: 0V, V_DD: 5V, V_SS: 0V, NC: 0V, SCL: 4.95V, SDA: 4.87V, NC(2): ~0V, A0: 0V, A1-2: 5V (address jumpers are both on), Reset+INTA+INTB: 5V, GPA0-7: 0V
MCP23017 #2: GPB0-7: 0V, V_DD: 5V, V_SS: 0V, NC: 0V, SCL: 4.95V, SDA: 4.65V, NC(2): ~0V, A0-2: 5V (jumpers), Reset+INTA+INTB: 5V, GPA0-7: 0V

Shorting V_DD directly to any of the GPIOA&B pins gets a relay click on both, so the relays work at least.

Statistics: Posted by phon0r — Thu Jun 27, 2024 2:29 pm

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