Your concept sounded sensible enough so I gave it a try-out.

First point is: The master always generates the clock so we don't need to multiplex that. We only need to multiplex the data (SDA).

Code snippet:

// the multiplexer address select lines (A/B/C)
const byte addressA = 6; // low-order bit
const byte addressB = 5;
const byte addressC = 4; // high-order bit

int selectTarget (const byte which)
  {
  // select correct MUX channel
  digitalWrite (addressA, (which & 1) ? HIGH : LOW);  // low-order bit
  digitalWrite (addressB, (which & 2) ? HIGH : LOW);
  digitalWrite (addressC, (which & 4) ? HIGH : LOW);  // high-order bit
  }  // end of readSensor

All you have to do is call selectTarget(n) where n is 0 to 7, and you redirect SDA to the desired chip. I suggest a 4.7k pull-up on the target side so that the line is pulled high when not selected.

I tested it out and it seems to work OK.

Your concept sounded sensible enough so I gave it a try-out.

First point is: The master always generates the clock so we don't need to multiplex that. We only need to multiplex the data (SDA).

Code snippet:

// the multiplexer address select lines (A/B/C)
const byte addressA = 6; // low-order bit
const byte addressB = 5;
const byte addressC = 4; // high-order bit

int selectTarget (const byte which)
  {
  // select correct MUX channel
  digitalWrite (addressA, (which & 1) ? HIGH : LOW);  // low-order bit
  digitalWrite (addressB, (which & 2) ? HIGH : LOW);
  digitalWrite (addressC, (which & 4) ? HIGH : LOW);  // high-order bit
  }  // end of readSensor

All you have to do is call selectTarget(n) where n is 0 to 7, and you redirect SDA to the desired chip. I suggest a 4.7k pull-up on the target side so that the line is pulled high when not selected.

I tested it out and it seems to work OK.

The beauty of this setup is that you can multiplex 8 devices (eg. sensors) which happen to have the same I2C address, with only one additional chip. And, you can get 16-channel multiplexers if you want to take this further. Of course, in the code you still have to select the correct I2C address for the chip.