@yveaux
I tried to use SoftWire in sketch without any libs and missed repeated start.

OK I finally managed it
The sensor requires i2c repeated start
But both Roger Clarks and official STM core for Blue Pill TwoWire libs don't support it.
Wire.endTransmission( bool stop ) where stop is just a stub and not processed
but SoftWire handles it
so just few changed to any lib (SparkFun/Adafruit/etc) like:

#ifdef ARDUINO_ARCH_STM32F1
#include "SoftWire.h"
#else
#include "Wire.h"
#endif

and
SoftWire SWire(PA1,PA2,SOFT_STANDARD);
#define Wire SWire

solves the problem
I hope this is useful to someone

@yveaux said in Blue pill (stm32f1) + VEML6075 UV sensor:

Can this be a problem?

I'm not sure if you can really trust the readings of this 'oscilloscope'.

I agree

You can try slowing down the i2c clock to make it visible.

100Khz is already minimum in blue pill Wire

The 10k pullup is rather high IMO for a 3v3 system, I'd rather try 4k7 or even lower. But you >say you already tried lowering the pullups.

but 10k works well in arduino 3.3v, arduino 5v with level converter to 3.3v. 10k BMP280 works with stm32
I ordered esp8266, it looks like someone is using VEML6075 with it

@yveaux
surprisingly but the sensor detected during i2c scan with correct address 0x10
I tried to explore dataflow using dso138 but this device is very simple, trigger works even at 50 us, clock looks like sine wave, but I see that some "1" on SDA are less that 3.3 volts, about 2 volts. Can this be a problem? However BMP280 sensor has the same but works well.
I tried 3.3v arduino and it works too. Resistance between sensor boards SCL/SDA and VIN is 10K just like BMP280

@Yveaux
I tried adafruit, sparkfun, schizobovine, Kris Winer libraries
Then I tried to work without library - the sensor is very simple, just several i2c commands

uint8_t msb = 0;
uint8_t lsb = 0;

Wire.beginTransmission( (uint8_t)VEML6075_ADDR);
Wire.write((uint8_t)reg);
Wire.endTransmission(false);

Wire.requestFrom((uint8_t)VEML6075_ADDR, (byte)2);
lsb = Wire.read();
msb = Wire.read();

To get device ID
But nothing works

Hi

Has anyone forced this pair to work?
My VEML6075 board works well with Arduino but not with Blue pill.
I tried both TwoWire and SoftWire, changing i2c freq, lowering pull up value (board has 10k resistors) etc
Other sensors (like bosch weather sensors) works well.