I2C and power

[camillerufu]

Hello,
I'am trying to drive servo motor through Adafruit 16-Channel 12-bit PWM/Servo Driver - I2C interface - PCA9685 board.
The power added on this board is 4 electric battery 1,5 v. But full voltage is around 4.9 v.
I can't access I2C device when i run "ls /dev/i2c*" : i2c is activated, blacklist are cleaned, etc...
Two questions :
- does i2c device exist on system even if board is not connected ?
- can the low level power (4.9v) explain that i2c is not operating ?

Best regards.

[PhilE]

Have you loaded the i2c-dev module? This provides the user-space interface to I2C devices, and is what creates /dev/i2c-1?
Just "sudo modprobe i2c-dev" to load it immediately, and add "i2c-dev" to /etc/modules to ensure it loads automatically after a reboot.

[camillerufu]

Hello,
Yes I have already done it. Thanks.

[joan]

Does your /boot/config.txt contain the following line?

dtparam=i2c_arm=on

[camillerufu]

The solution was:
To have simultaneously the following settings:
In /boot/config.txt:
dtparam=i2c1=on
dtparam=i2c_arm=on