10DOF I2C/SPI MPU9250 BMP280 GY-91 only see BMP

Other Hardware Sensors
1

i just hooked up one of these
https://www.ebay.com/itm/10DOF-I2C-SPI-MPU9250-BMP280-GY-91-BME280-Kompass-Barom-for-Arduino-Raspberry-Pi/222324066604
which should have a MPU9250 and a BMP280, i assume both connected to i2c
these doesn't seem to be any docs
when i do i2cscanner i only see device at 0x76 and that is the BMP280 which is working

so question is, any one know how to access the MPU? thx

the only docs i'm seeing are here

VIN: Voltage Supply Pin
3V3: 3.3v Regulator output
GND: 0V Power Supply
SCL: I2C Clock / SPI Clock
SDA: I2C Data or SPI Data Input
SDO/SAO: SPI Data output / I2C Slave Address configuration pin
NCS: Chip Select for SPI mode only for MPU-9250
CSB: Chip Select for BMP280
i have VIN,GND,SCL and SDA connected, everything else is O.C.

i just found this
68 is the I2C address for MPU9250, and 76 is the I2C address for BMP280
here http://ecorov.com/2017/08/03/i2c-gy-91.html

2

I just tried another nano and another MPU9250 BMP280 GY-91 board and exactly the same so i think not simply bad hardware

i also tried tying the other 3 pins to GND and nothing

3

any help please? i'd like to use this sensor but right now its useless to me. no one else used one before?

thanks

4

Hi steveh2112,

It appears that the GY-91 board has on-board pull-up resistors for the chip select and AD0/SDO lines. (Note that unlike the SCL and SDA lines these signals are not +5V tolerant and should be left unconnected, or only be used with +3.3V).

The AD0 state determines the least significant bit (LSB) of the MPU9250's I2C address. If the AD0 line is pulled high (to +3.3V) then by default the MPU9250 will have an I2C address of 0x69. If on the other hand the AD0 line is pulled low, the I2C address becomes 0x68.

The MPU9250 also has an on-chip magnetometer, it's an AK8963 device at I2C address 0x0C.

For I2C operation both the devices' chip select lines should be held high, (or in your case left unconnected).

5

thanks but unconnected isn't doing it since i2cscanner is only seeing 0x76, the BMP

i'll try some pullups to 3.3v

6

This seller seems to have a schematic and it shows the level shifter Mosfets have pullups on the SDA/SCL lines.
The Wire library uses twi helper and in there it enables internal pullup of the SCL/SDA lines.

  // activate internal pullups for twi.
  digitalWrite(SDA, 1);
  digitalWrite(SCL, 1);

Maybe try disabling the internal pullups just in case they and the Mosfet ones are to much.