ESP32-PoE-ISO-16MB --> MOD-IO --> BME280

[swaff]

I've got an ESP32-PoE-16MB connected to a MOD-IO via the included UEXT cable, and a BME280 plugged into the female UEXT on the MOD-IO board.

I'm having an issue where the humidity reading from the BME280 drops out. I've tried reducing the frequency and oversampling rate, but to no avail.

I'm wondering if anyone else has had a similar problem and can offer any solutions.

I do have a second BME280 sensor that I swapped out which didn't change anything.

[LubOlimex]

Try without the MOD-IO and see how it goes. Just connect the BME280 to the UEXT of ESP32-POE-16MB. This will show if the issue is somehow the MOD-IO board. If that is the case consider connecting the BME280 before the MOD-IO, maybe use UEXT splitter like UEXTx5 or make similar:

https://www.olimex.com/Products/Modules/Adapters/UEXTx5/open-source-hardware

[swaff]

I have tried plugging just the BME280 in and it works fine. As far as I can tell, it seems to be an issue with I2C communication.

[LubOlimex]

1. How do you power the BME280? If you want to power it from the MOD-IO, it will not work since the 3.3V powering is disabled by default (to avoid accidental short-circuit). Refer to the schematic. You either have to close the pads left for the resistor (or place 0R resistor size 0603) or connect both MOD-IO and BME280 in parallel to the ESP32 board.

2. How do you power the MOD-IO? Is it via the power jack?

3. What exactly is the BME280 module and how do you connect it to the UEXT female connector?

[swaff]

This is the Olimex MOD-BME280. It is connected directly to the MOD-IO via UEXT (no cable). The MOD-IO is connected via an included cable to the Olimex ESP32-PoE-ISO-16MB UEXT port.

The MOD-IO is powered via the jack. I've tried both USB and PoE power to power the ESP32 with no change.

The MOD-BME280 is powered via the UEXT connector as I thought that's how it was supposed to work. And most of the time it does work, but sometimes the humdity reading disappears, and even more rarely I've seen temperature and pressure stop working.

[LubOlimex]

It is clear then. In your case MOD-BME280 won't get powered properly. Basically the 3.3V output from MOD-IO is disconnected. In the way you use it, MOD-BME280 gets parasitically powered via the I2C lines. This is side effect and a problem, it is not a feature or a recommended way to use the boards together.

In order to enable the 3.3V output at the UEXT_FEMALE header, you need to solder R16 on MOD-IO board. It is located just under the UEXT_FEMALE connector on the top of the board.

We've disabled this 3.3V line by default to avoid short-circuits when multiple MOD-IO boards are connected (and each powered from own power supply). But in your case you need to simply solder 0R resistor size 0603 on R16 pads and things will start working properly.

Again refer to the schematic to understand better:

https://www.olimex.com/Products/Modules/IO/MOD-IO/resources/MOD-IO-schematic.pdf

The alternative is to connect MOD-IO and MOD-BME280 in parallel (e.g. not MOD-BME280 after the MOD-IO). This way MOD-BME280 will get powered from ESP32-POE-ISO (where 3.3V output on the UEXT is enabled by default).