How to use 74LS138 or 74HC595 to muliplex two I2C signals?

Other Hardware LEDs and Multiplexing
21

Just use a 74HC4052. It's made for the job.

One extra pin to control it. A second pin can multiplex a total of four I2C devices. Just check that I2C handshake is complete before switching.

Uses the same switching technology (essentially MOSFETs) as the one Crossroads quoted. Need to provide separate pull-ups for the two switched channels.

"On" impedance is better than 80 ohms. If you wonder whether that is too much, keep in mind that it is actually similar to the impedance of your Arduino output.

Will multiplex 3.3V levels with no problems if you power and control it from 5V. (To control it from 3.3V use a 74HCT4052).

How much easier do you want?

22

If it's only 2 devices you could use a DPDT relay.

23

raschemmel:
If it's only 2 devices you could use a DPDT relay.

You could but - why on earth would you? :astonished:

24

Fewer pins than a MUX ?

25

raschemmel:
Fewer pins than a MUX ?

But its not more Arduino pins if you are only using 2 buses.
1 pin selects between them.
And then there is the issue of power to the coil, and size, and slowness of using a relay.
http://forum.arduino.cc/index.php?topic=269115.msg1898314#msg1898314
--- bill

26

Ok, just for the sake of discussion since there is NO communication at the moment , there's no harm in entertaining another approach, what exactly is the OBJECTIVE of this WHOLE project ? What is the time/speed or data transfer criteria ?