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By virosh
Hello All!

First i need to say that i am not very good at electrical stuff, but decided that i can build this myself and now i am stuck.
I have an Arduino Pro Micro 5V version and MPU-9150 which is 3.3V (i should have checked the specs before buyng but...).
The Arduino is powered via USB as it needs to be connected to the PC to work. It is a headtracker, you place it on your headphones and it tracks your head movements providing the data to the game you are playing. The actual project is not mine, but i decided to try and build it myself using the provided data -

Now the problem i am facing is that for some reason i am not able to power up the MPU-9150. Let me explain.
If you connect it directly via the Pro Micro - it may work, but it will be unstable and most of the time it will not power up (which is good so you don't smoke it).
I made a voltage divider:
(5Vin -> R1 1KOm -> 3.3Vout -> R2 1.8KOm -> GND, the MPU-9150 has two 10KOm resistors in place so the RL is 20KOms)

Lowering the 5V to somewhere around 3.2~3.3V in order for the MPU-9150 to be properly powered. The voltage is correct (i checked it), but the MPU is still not working as expected. Yes it power's up, but the sensor does not transmit any data. I am using the MPU-9150 raw sketch for testing.

Then i decided to test it with one smoked Pro Micro 3.3V which currently can be used only as a PSU.
Connected the VCC from it towards the MPU and magic... it worked. I checked the voltage is is almost the same as the one provided from the divider.

And now i am stuck as i cannot understand what to do to power up the MPU-9150 properly.

Any help is greatly appreciated.

Thank you!
By waltr
Run the Atmega processor from 5V (USB or a regulator) then use a 3.3V linear regulator to power the MPU9150.
The next issue is the logic levels of the two chip on the I2C bus. For this use a FET level shifter, SparkFun has these.

Using resistor dividers to power chips is a bad idea which can be un-stable, uses power and produces heat.