Power consumption of I2C bus

Hi everyone,
I have a project of low power camera, using an Arduino pro mini (with watchdogs), a camera, and a RTC timer, both working with SPI bus.
In order to save battery, I use TIP122 transistors to switch of power pins to camera and RTC.

My question is simple : is it enough to limit the power consumption, or do the SDA and SCL draw also current ?
If yes, is there a way to 'completly' disconnect it ? Maybe with BJT transistors ?

Thank you !

If you cut the high side (5 V) power to the I2C bus devices, the bus pull-ups which tie to 5 V, will draw current and “phantom” power the various devices, so you have to disconnect the pull-ups from the 5 V also. An Arduino pin can do this easily.

Thank you very much Paul__B !
My pull up resistors are already in the chipcard (I use DS3231 for RTC, for exemple)

I cut the low side (GND) of my I2C device. Is it a problem for the power consumption ?

SPI or I2C?
Low side switching should be OK. Why do you cut power to the RTC? It defeats the purpose of the (very accurate) RTC.

Smajdalf:
SPI or I2C?
Low side switching should be OK. Why do you cut power to the RTC? It defeats the purpose of the (very accurate) RTC.

It is I2C.
My RTC module as a small battery for it, I want to cut power from the 5V pin, which is used by LEDs on the chip board and other things. :slight_smile:

Could you please post a schematic of your circuit?

Are you using the TIP122 for a particular reason? It's a Darlington as I remember.

The I2C lines have pullup resistors. On the RTC these resistors pull up to the Vcc header. But if you are switching off the RTC module's ground connection, I don't see how there could be any current flow. There would be no return path. But the test would be to measure the current at the Vcc pin with your meter. I don't know about the camera.