Hi everyone, I have a Jhemcu play F4 which i am trying to add a barometer to (yes, the ever popular nano-longrange fad  )
I found a few tips on how to add I2C devices, but of course nothing for this particular FC. I figured the process should be like this:

1. Determine which pins can be used for I2C on this CPU (STM32F411CEU6). According to the datasheets

I2C #1 can use PB6 or PB8 for SCL, PB7 or PB9 for SDA
I2C #2 can use PB10 for SCL, PB9 or PB3 for SDA
I2C #3 can use PA8 for SCL and PB4 for SDA

Of those available pins, only I2C #2 PB9 and PB10 were available on this board, others assigned to various functions. Is that the correct way of looking at it? (The betaflight I2C tutorial i found online just said "refer to your board's pinout")

2. Then take a deep breath, and solder some enamel wires to those pins on the FC (which i somehow managed to do).
   

3. Now, enable the pins in CLI:


(PPM 1 was set to B10 originally)

4. Finally, solder up a 5V BMP280 (https://www.aliexpress.com/item/32817286611.html?)... Is this where i stuffed up? Should this be the 3.3v version? No Barometer detected in Betaflight, but Status CLI returns "i2c errors: 0"

Does anyone have any experience with this, can you tell me if my process was wrong here? I hope my pin selection is correct because i now have a glob of E6000 over the wires for strain relief...

Just realised i hadnt set baro_spi_device = 0... but changing that didnt solve it. Diff All is as follows, dump is attached:

Try to use the default I2C address.

Are there pull-up resistors on the barometer board?

Thanks, i just tried setting address to zero, no luck unfortunately.

Regarding the pull up resistors... i'm not sure!
   
There is that weird 1k resistor (4 in 1?) on the bottom, not sure if thats the pull up

I'm mainly concerned about the voltage... I just checked GND/SDA and GND/SCL and there is 5v on those pins, which seems a bit much for the MCU?

I think that 4-in-1 is the pull up resistors.
From what i can make out, the underside of this module has the 3.3v LDO, and possibly a two channel mosfet?

I just checked, and PB9 and PB10 are both 5v tolerant (phew)

But it means something else is stopping this from working.

Maybe an LED on each of those pins, controlled by a Box IO to at least see if the pins are correct? Havent done that before, just clutching at straws

Check the resistance between SDA/SCL and the Vcc pad on the mag. If it's not somewhere in the 1k-5k ohm range, you may need pull up resistors.

Edit: I just found two more issues, you have baro_bustype set to SPI, and there is a resource conflict with ESCSERIAL.

Try:

So far no luck. Adding resource PULLUP gave me an I2C error where previously i had 0. Its a step forward perhaps?

I have taken everything else off B10 (PPM, ESCSERIAL, timer, dma pin), still no luck

Adding the PULLUP resources let me measure 3.3v out of my enamel wires, so i am quite certain they are connected to the MCU pins correctly

I have tried adding physical 1k pull up resistors on SDA/SCL.


Another possibility is just a bad module. Or possibly an issue with supplying 5v on those pins (they are 5v tolerant though... Is that "we will tolerate you but we still dont accept you as our friend"? or "we can handle all that high voltage you are throwing at us, lets be friends!"?)

You are lucky, I have gone through 5 of those FCs and have sworn them off due to high failure rates..
RDQ still stocks them, they said even with them failing some people like them... @25 a pop, it’s a bargain AND it’s 2s capable..I see why. I just feel REAL bad getting one, either having a bad esc, no osd, or just doa.... contacting customer service ...and they were from different suppliers..