Galvanic decoupling of I2C bus


Posted on Aug 18, 2012

Since the speed of the I2C bus can be rather high, it is recommended to use a fast optocoupler. However, this circuit will not work on speeds higher then 10KHz. A 6N139 will do the job in all cases. The two PNP and the two NPN transistors can be any standard type, e.g. 2N2219 and 2N2222 (USA) or BC547 and BC557 (EUROPE).



The problem with bi-directional lines is that a buffer tends to get stuck on a certain level. This case has been taken into account in the above schematic. In the following explanation we assume that the left side is transmitting and the right side is rec




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