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Help with possible I2C interfarencde

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DrG:

--- Quote from: cmumford on July 13, 2020, 06:48:08 pm ---I didn't add one. Would this be part of the developer board (https://smile.amazon.com/gp/product/B07KYJNFMD) or something I need to add myself?

Edit: Looking on the schematic (on Amazon link) this is provided by the dev board.

--- End quote ---

The schematic on your link shows 10K pullups.

Twoflower:
Yes, and also the LDO and level-shifting circuit should not be a problem.

At which speed do you run the I2C? Have you tried to run it slower? Otherwise I would check the nature of the problem (HW or SW). That the sensor-readings seem to stuck at a max-level (225F) could indicate that the sensor I2C state-machine get's messed up. So can you just power-cycle the sensor-board after that happens (of course you might to configure the sensor)? Does the problem goes away? That could indicate to EMI issues.

mikerj:
Sounds like the BME280 is leaving SDA pin pulled low, which means the master can't even assert a stop condition on the bus.  On many I2C slave devices this situation can be recovered by toggling the SCL pin until the SDA pin goes high (up to 9 clock cycles), but better to find the cause.

IMO there is a strong possibility that you have some marginal timing, but you really need to scope to check this.  Failing that my suggestion would be to try increasing the strength of the pullups (1k or so) and/or maybe reduce the I2C clock speed.

cmumford:
Thanks everyone. Arduino defaults to 100K bus speed, but can be changed (sometimes slower) depending on the chip. I'll try that first. I do have a DS1054Z, and will connect it once I have the board pulled from the case. Thanks again for the assistance.

DrG:
I am anxious to see what happens. If you read the comments on those boards, there are some that suggest that some were pretty low quality, including ones that were likely BMP rather than BME - something I have also seen on boards from the bay, although I don't think that particular situation is the case with the OP.

That 1/3 work and sometimes the bad ones work for as long as 90 min smells bad as a product. Yeah maybe something marginal.

One last thing. If you are primarily interested in ambient temperature or if ambient temperature is a main need, I would not use that sensor. If I remember correctly it is a die temperature and not advertised as being ambient temperature.

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