SI7021 not visible in weathershield [solved]

[RTFM]

Hello,

I'm about to run the weather shield, BMP180 and SI7021 as sold and solder by LowPowerLab on a ordinary 5V Arduino.

I having issues to get SI7021 to work. Problems arose early already: The sensor.begin() - it fails.
Having a look to the library, to
  SI7021::begin()     
  ......
  if (Wire.endTransmission() == 0) {
          _si_exists = true;

Wire.endTransmission() puts back value "2" always.

Applying the I2C Scanner, I receive :
Scanning...
I2C device found at address 0x27  !
I2C device found at address 0x77  !
done

-  0x27 is my LCD display,
-  0x77 is the BMP180  of weather shield ---> At least weather shield is on the bus. 
    Btw, the pressure values I obtain using BMP180 are OK.

1) Where is the "0x40" of the SI7021? Why it is neither not addressable nor even recognised?

I have soldered 4 Pins: 3.3 V, Gnd, SCL,SDA
2) Is there something I have to solder or remove additionally? At the copper plates at "pullup", may be?

Thanks,
RTFM

[syrinxtech]

Not making any assumptions, but I'm guessing you have the following in your code:

#include <Wire.h>
#include <SI7021.h>

[Felix]

Your wiring seems correct but i have no way of verifying the 3.3v signals going into your 5v arduino will be registered.
I am interested to see if this works on a Moteino, with the sketches I have provided: https://github.com/LowPowerLab/WeatherShield

[RTFM]

Hello,
Thanks for your answers, that pointed me to right direction.
I was aware of the 3.3 V issue at a 5 V Arduino and installed one of this Bi-Directional level shifters.
From that side: All OK.

But my 3.3V bus is, because of it's consumption, a 5.0 V bus minus the drop out voltage of 2 SI-Diodes, what computes to 3.6 V, a bit more or less. But 3.6 V is the  maximum of SI7021 as per data sheet.
Now I'm using the Arduino built in 3.3V Power supply - the SI7210 appears in IIC scanner and it can be used by the software.

Thanks,
RTFM   

[Felix]

So .. Solved?

[RTFM]

yes