QwiicBus behind i2c mux

Qwiic System
1

I need to use the QwiicBus to support two ToF sensors over a few meters. The sensors (VL53L1X) have a fixed address so I need to use the 8 port I2C mux to enable multiple devices. I can put the sensors (and other I2C devices) behind the mux and scan them just fine.

I can also hook up 1 sensor (or another I2C device) to the QwiicBus (connected directly to the I2C bus) and see that just fine.

The issue is that when I put the QwiicBus behind the mux, I can no longer see the devices on the other end.

Has anyone else been able to make this configuration work? If so, did you need to mod the QwiicBus endpoints?

2

That should work just fine.

What happens if you eliminate the Qwiic Bus alltogether and just connect the MUX and sensors directly to your system?

3

Thanks for the reply!

Other configuration notes:

  1. The VL53 have their pulls-up disconnected

  2. The system is a P1AM-GPIO module from automation direct. This is a break out to the MKR zero based P1AM industrial Arduino device

  3. I have QwiicBus endpoints both with and without the I2C pull-ups

Experiments/results:

  1. VL53 and Mux direct to the I2C bus - scans see both

  2. 2 VL53s behind the mux - scans see the mux and both sensors on the right port

  3. VL53 on Qwiicbus (No PU) on I2C bus connector on Mux - bus hang (expected since no pull ups in system)

  4. VL53 on Qwiicbus (PU) on I2C buss direct - scans fine

  5. VL53 Qwiicbus (PU) on I2C buss via connector on mux - sees Mux, but not VL53. I think this is expected as the mux is going to grab the bus traffic and send it down a port (correct?)

  6. VL53 Qwiicbus (PU) on Mux port (7) - Mux seen (0x70) but not VL53 (0x29)!?!

  7. VL53 Qwiicbus (PU) on mux port (7) + VL53 Qwiicbus (NPU) on mux port (4) - bus hang on scan of port 4 (aren’t there PUs on the ports?)

4

Ok, so I replaced my P1AM with an Adafruit M0 Feather and things seem to work perfectly now. I can see the ToF sensors behind the mux w/o issue.

There must be an issue with the I2C bus on the P1AM system. Off to debug that now

5

Ok, final follow up FWIW. I connected the I2C bus directly to the P1AM header (instead of the P1AM-GPIO module) and it works fine. It seems the GPIO module is the weak sauce here. Not sure why and don’t care.

I think the conclusion is that if you want to use I2C externally with the P1AM system you should NOT use the GPIO system. I am going to build my final system using the proto board.